5 - Watering, part I: H2O and the plant. Frequency of watering

If your plants suffer shortage of light for a while, they will tolerate it. But water deprivation will kill them. As we know, water is essential for germination and growth. And as usual, every type of plant, and every stage of growth, shows different needs; cacti and succulents store moisture within their tissues and are able to manage well in case of drought, but leafy seedlings have no reserves and the time between getting slightly dry and dying goes by very fast.

Each plant has different tolerance to wilting and has different ranges for recovery. Partial wilting, while better avoided, is not fatal; the little brown ends in leafs, well known by salvia or chacruna gardeners, are a result of localized partial wilting, and they are not a disaster – but they should be a warning sign, as long as you understand that language.

So, once again, the gardener's homework includes this as a key assignment: Know Thy Plant. Being aware of the particular needs of the plant you want to grow, and understanding some principles about watering, is all you need to be able to keep your plants well greased.


5.1. – H2O and the plant

Plants use water to:

- Feed and regulate the metabolism of the plant.
- Transport around the soluble sugars produced in photosynthesis and the mineral ions fished by the roots.
- Maintain plant structure, keeping the plant turgid and able to support its own weight.
- Protect the plant against wide temperature fluctuations, thanks to water transpiration in the leaves.

Water is also essential to dissolve the mineral nutrients available in the substrate, so the roots can capture them by osmotic exchange.

Besides the digestion of water in the chloroplasts, the little photosynthetic machines that break down H2O using the energy of light, there's two other water-related components in plant anatomy that you should meet.


Stomata (singular: stoma) are tiny pores generally concentrated on the underside of the leaves, out of direct sunlight. They are the responsible for the gas exchange in plants, acquiring carbon dioxide from the air and releasing oxygen as a byproduct of photosynthesis. (In a side note, the output oxygen is larger than the input of CO2, which explains the air purifying effect of the plants and the fact that all animal oxygen-breathing life in the planet owes them at least a fist bump.)

Normally, stomata open when the light strikes the leaf and triggers the whole photosynthetic process, and they close at night time. Stomata also perform an important role in the immune system of the plant, reacting to the intrusion of bacterial compounds - not unlike what happens in the mouths and other openings in animals. The lips of stomata, called guard cells, modify their structure when exposed to blue light thanks to a change in osmotic pressure.



It's no wonder that the highest levels of osmotic pressure, and hence the widest opening in stomata, occur at noon in plants growing outdoors, when the sunlight energy is at its peak. High carbon dioxide concentration and high humidity also favor the opening of stomata.

Another key process they allow is the evaporation of water towards the atmosphere, called transpiration. This is the plants way of sweating, and although it occurs as a side effect of having their mouths open allowing the water vapor out, transpiration carries out essential functions for the plant: It helps to regulate the temperature in the plant surface, and by changing the hydrostatic pressure in the plant tissues, also pumps up water and minerals from the roots in another chapter of osmotic exchange. Which is to say, when the feeder roots sense water shortage in the soil, stomata will close to keep the precious water available. This defense system has a limited efficacy, though; the water shortage will eventually make the plant suffer and might be fatal.

Stomata are formed during the initial stages of plant development, and therefore they reflect the environmental conditions under which they grew. For instance, plants of the same species growing in different levels of ambient humidity will show different density of stomata. A sturdier plant used to drier environment will develop less stomata as a way to decrease the loss of water by transpiration; that, of course, decreases the photosynthesis rate, making the plant grow slower when compared to another individual in a more humid environment.


Vacuoles are cell components (organelles) that are shared by most plants, animals and fungi. They are multifunctional, although generally serve as storage compartment. Most plant cells have one large vacuole that can occupy from 30% to as much as 90% of the cell's volume.

In ideal conditions, they are basically full with water, which sustains the shape of the cell (hence the structure of the plant tissue) and allows storage of minerals, proteins, enzymes, and waste products. They are also responsible for the straight structure of the plant thanks to hydrostatic pressure.



Many of the valuable tryptamines you have extracted have been patiently stored inside of the plants vacuoles until you eagerly broke their walls with physical and chemical alterations.



5.2.– Frequency of watering

There's two ways your plants will lose water: evaporation from the substrate, and transpiration from the leaves. Other than that, water is indefinitely recycled, exactly as in the larger scale of things.

You should water more or less often depending on several circumstances:

a) Age and Growing stage. Young plants need frequent, light watering since they do not have yet the resources to make up for water shortage. Mature plants that are in a quick growing period will make good use of frequent watering too. Whenever you are reproducing or following seasons, plants that are coming out of the rest period often associated to winter (when water requirements drop significantly) will appreciate having more water available. So if you have a spring in your indoor, more water will be welcome. A known extreme example of this can be found in lots of cacti and succulents, that will do fine with barely any water during their winter rest season and will subsequently welcome early spring water.

b) Ambient humidity. For the aforementioned reasons, a high ambient humidity will decrease transpiration (and increase capture of water by the leaves) and lower the amount of evaporation from the soil, which decreases the frequency of watering.

c) Temperature. Heat increases transpiration, as you know. We drink more in summer too.

d) Air flow. If the air under the leaves moves more frequently, it will nicely refresh the CO2 available but also blow the water vapor away, so the plant will replace it more often. So using abundant ventilation also raises the need for water. However, we must assume that any specific watering guidelines for a plant presume ventilation, so the practical consequence of this goes the other way: plants with reduced air flow, or isolated from air flow, require less watering.

e) Flowering and fruiting periods, where most plants will need some extra water.

f) Repotting times. Generally, if the plant is pot bound and has to be repotted soon, it will need more water than if it has been just repotted. The reasons for this are several. First, the growing substrate in a pot full of roots holds water worse and drains faster. And second, the plant and its root system will be bigger than ever before in that moment. When we have just repotted a plant, and once we have made sure that the new substrate is moist enough, we don't want the roots to be lazy; we want them to get to work and dig deeper looking for water, and a little less frequent watering (while making sure that the other needs, specially light and air, are well covered) will help the plant grow downwards rather than upwards. And that's the first requirement for her to be able to grow upwards as we want her to do.

The most important of them all, though, is the particular needs of every type of plant. You are highly encouraged to learn about the documented water requirements of the species you are growing. Plants might require a substrate slightly dry, moist, or thoroughly moist, and that will determine whether you have to check/water them weekly, every three or four days or every other day. If you cannot find specific information about your plant's water needs, learn about the natural conditions the plant grows in and do your best to reproduce them. Until you get well acquainted with your plant, it's a good idea to check on it often.

To sum this up:

- You should water the plants more often if they are seedlings, if it's hot, if it's dry, if it's growth (spring-summer) season, if they're flowering, if they are under abundant ventilation or if they are root bound.
- You should water your plants less often if they are in a rest period, if it's very humid, if it's cold, if there's poor ventilation or if they were just repotted.

Other than that, you should water them follow the average needs for the species you are growing.


In any case, a continuous wet substrate is generally to be avoided. We don't want the roots to drown or to rot. For most plants, it's better to water regularly than drowning them after a period of drought. So good balance is the key. Keep in mind, though, that very frequent and shallow waterings are generally not beneficial. Doing that promotes root growth closer to the surface, where roots are more vulnerable to drying out. We want to promote roots digging deep instead, so go for thorough, well drained watering every X days, as needed.

As for the best time to water the plants within the day period, you should water the plants if possible in the beginning of the light/day time. This way you give the plant the whole day to use the water, and lose less water to evaporation. Also, watering in the evening serves better the interests of fungi that thrive better under dark and moist conditions.


Now that we've discussed why and when, in the next post I'll talk a little about which water to use and how to deliver it. We already know about the who. In this case it's you instead of the rain.

Thanks for reading

6. Watering, part II: Which Water to Use and How

6.1.– Choosing and preparing water

Besides the H2O molecules themselves, water can carry minerals and other chemicals in solution. And those can be already present in your base irrigation water, can be added to it before watering, and also will be already present, undissolved, in the soil.

If you understand the growing medium as a chemical system, you can think of water as your delivering device to fuel or change that system, making sure that the plant is able to do her job in it. Think of the plant in a symbiotic relationship with the soil.

The ideal water to start with would be the closest thing to pure H2O you can get. That means either distilled (or de-ionized) water, or light spring water if possible. In many places, tap water can be very hard (too alkaline) and it often contains an excess of chlorine. Careful gardeners using tap water will leave it resting in an open container for 24+ hours to allow the chlorine gas to evaporate. Of course you could use right away any clean type of water for your plants, and just skip this information, but if you want to take really good care of them, you'll make sure that your irrigation water provides what your plants need – and nothing else.

For that, there's two key values you should be familiar with: pH and EC. Both have to do with the concentration in water of elements other than the H2O molecule.

I'll discuss them in this chapter, although they are directly related to the chapters about Substrates and Nutrients as well.


6.1.1. – pH

pH, standing for potential of Hydrogen, is a measure of the activity (ion concentration) of the H+ ion in a water solution. It's a 0-14 decimal logarithmic scale, so the difference between two pH consecutive values is a 10x factor. Since the pH value is a negative logarithm, one substance with pH=5 will have ten times more H+ ions than a substance with pH=6.

Solutions with a low pH (<7, more H+ ions than OH- ions) are called acidic, solutions with a high pH (>7, more OH- than H-) are called alkaline, and a value of pH=7 is neutral, which means there's roughly as many H+ ions as OH- ions.

When we talk about the ideal pH range for a plant, we are essentially referring to the pH range the plant requires to keep the physical-chemical machine running well, and that means the pH in the growing medium. The soil pH determines the chemical processes that may or not take place in it, specifically affecting nutrient availability by controlling the chemical forms of the present nutrients.

Every plant has a more or less specific pH preference, so if we can control the pH in the substrate, we get rid of yet another limiting factor for our plants. Most plants have an optimum pH range between 6 and 7,5. Generally, to ensure nutrient availability, slightly acidic soils are better than slightly alkaline soils.

The pH in the soil is determined by the presence of mineral salts and microscopical life. The right way for controlling it requires measuring the soil pH when you prepare your soil before planting. This is important because changing the soil pH afterwards can be a long and difficult process.

You have several options to measure pH values:

- Litmus paper, which you can directly use to measure the pH in your water, or to measure the pH of the soil by dissolving a pinch of soil in distilled water and then inserting the litmus paper strip. A dark band will cover the number corresponding to the pH in the sample.



- Chemical pH testing kits are available both in powdered form (generally barium sulphate) or liquid form. One drop of the reactive is added to the water sample to be measured, returning a color that can be checked against a color table with the corresponding pH values.



- Electronic pH meters are more expensive, but they are the most precise and versatile option, and a good investment in the long run. There are meters for water, and rod meters that can be inserted directly in the soil when it's moist (don't try to measure pH in dry soil; you won't measure s**t and you might break the sensor). By inserting the meter in the moistened soil or the water, and waiting the time specified in the operating instructions (generally 2 minutes minimum) you will get a precise measuring of the pH. These meters have to be properly cleaned with distilled water after using or they will stop being reliable, and should be stored in a dark, cool place.



Spending money in analogic meters of any kind (the non-digital, with a measuring needle) is not a good idea. These meters are not precise and break easily, so if you want to get a meter, purchase a decent one.

Now, an important fact: The pH of your irrigation water will NOT change permanently the pH in your substrate. We might find out that our substrate is too acidic, then water with slightly alkaline H2O, measure immediately, see that the soil pH has raised and think the problem is already solved. However, after a few hours the soil pH will be back at the initial value. Again, it's important to start using soil with an acceptable pH value.

A good pH in water (by default neutral, or slightly acidic) is important to make sure that the nutrients in the substrate can be dissolved in it after watering. Using water too acidic or too alkaline will keep lots of nutrients undissolved, and they will accumulate saturating the soil, altering further the soil pH and starting a vicious circle we definitely want to avoid.

Whenever you want to adjust pH in your water, you can lower it by providing H+, that is, adding an acid. You want to use an acid that does not carry any toxic ions for the plant; citric acid and vinegar are fine, but you can also use nitric acid or phosphoric acid, which will provide basic nutrients for the plant as well in the form of nitrate and phosphate ions. Reversely, you can raise pH in your water by adding an alkaline substance such as lime or sodium bicarbonate.

In both cases, the proper way of deciding how much to add would be by doing the numbers (you have a nice basic chemistry thread here) but if you want to eyeball it, have your pH measuring device/litmus paper handy and add very small amounts, step by step. Remember that a little dash of vinegar will greatly lower water pH.


6.1.2.– EC

EC stands for Electro-Conductivity, and it is a measure of the ability of a material to conduct electric current. In gardening, EC can be understood as a measure of the concentration of salts and nutrients dissolved in a medium. It can be monitored in both substrate and irrigation water. To make an illustrative point, distilled water has an EC=0 since there are no salts dissolved in it.

Measuring EC will let us know the exact amount of nutrients we are delivering to our plants when watering, or how much food is held in the soil. For this we will need a digital EC meter. The general guidelines for pH meters above can also be applied to these.



The most common unit for measuring EC is MilliSiemens per centimeter (ms/cm). In different meters or reference materials you can also find p.p.m. (parts per million) or CF (Conductivity Factor) measurements. Here is a conversion table for your convenience.



The EC value provides a lot of information by itself, but if we combine it with pH monitoring we'll be able to completely optimize the diet of our plants. EC is particularly related to the amount of nutrients the plant has available, but it also reflects the unnecessary minerals in the water we are using, such as excess sodium or calcium in hard waters. If the base water we are using has an EC higher than 0,3 ms/cm, it might be convenient to mix it with distilled water (EC 0) so it can work better to dissolve nutrients in the soil or to drain away any excess of nutrients.

As we said before, roots feed thanks to osmotic exchange. When the concentration of elements and salts is higher in the plant than in the soil, the water (along with the dissolved nutrients) enters the plant trying to balance concentrations and achieve equilibrium. And when the concentration of salts is higher in the medium, the plant will lose water. That's why an excess of nutrients in the soil (EC too high) can be fatal for plants, causing severe dehydration.

Different plants will appreciate different optimum soil EC values. In widely known and researched indoor plants like cannabis, for instance, an ideal EC in the soil is around 2 ms/cm, and the gardener should not allow it to go below 1 ms/cm. Strong lights, or high CO2 availability, will increase the consumption of nutrients and might alter that range a little bit.

Measuring the starting EC value in the moist soil you prepare for the plant will give you an idea of how much food has the plant available for starters.

Excess of nutrients can be slowly fixed by washing the roots (either watering for some time with excess distilled or very low EC water, letting it drain thoroughly, or even washing by immersion in emergencies - see 6.2.2 below) but ideally we'll prevent any nutrient excess by controlling the EC in the soil from early on, and also by measuring the EC of the water we are giving to the plant.

Whenever you find low nutrient levels in the soil (say, below EC 1) do not fertilize or supplement your irrigation water right up to EC to 1,8 or more. Plants will easily overeat when a lot of food is suddenly available, and that type of sudden fluctuations are not good. Raising the EC of the growing medium should be done progressively, increasing the EC value of the water step by step (say, +0,2 EC each watering time) until further soil measures return a correct value. A little experimentation will give you the values your plant like the most.


A final hint to effectively measure the pH and EC values of your soil: use percolation. Water your plant as usually and let it drain well. After an hour, place the pot on a clean plate and water with distilled/deionized water in slight excess, to gather in the plate 50 ml or so of newly drained water. That water can be used to measure reliably soil pH and EC values.


6.2.– How to water your plants

The two major ways to water a plant grown in a container are from above and from below. Before talking about their differences, it's important to keep in mind that different plant morphologies will appreciate different watering methods.

6.2.1.- Watering from Above

Since we are imitating earth, sun and a proper atmosphere, we might as well imitate rain.

The best way is always watering slowly. Remember that you are not stuffing water inside of the soil, or just pouring a lot of water for the plant to choke in. We want the substrate well hydrated, and that takes some time; pouring all at once means a lot of water will drain out following the channels through the partially dry substrate, leaving not enough time for the growing medium to absorb it. At the same time, a lot of water delivered at once will push the soil down, compacting it and reducing the ventilation of the roots.

The objective is to reproduce the effects of natural watering: light rain, or morning dew for some species as well. Ideally, you will have a watering can available and you'll benefit from the fact that water droplets are more efficient than water streams at carrying oxygen into the soil.

Ideally, you will at first water enough to get the top layer of the substrate thoroughly moist so the rest of the water will enter the soil uniformly. This is particularly convenient when the soil is dry. The drier the soil, the longer the time for it to absorb water and rehydrate.

Another way to understand watering from above is misting. This is the slowest (and most careful) method, and although you could always use it, it's specially convenient when you don't want to alter much the surface of the substrate, like in germinating trays, little greenhouses and when watering cuttings that are in the process of rooting and do not have yet a grip in the substrate. For this you will need a spray bottle and it follows the same logic. My way of gentle watering starts with misting the soil surface well, waiting for a while (15 minutes will do, but longer might be necessary if the soil was dry) and then watering slowly with a can until water starts draining down to the plate.

Unless you are growing plants that like particularly to get wet, it's better to avoid soaking wet the whole plant when watering, so most times we'll deliver the water straight to the growing medium. But some plants will enjoy a good shower, and others like water delivered into their central cup, rather than directly in the pot, because they rely on absorbing moisture through their leaves as well as their roots. That's for you to find out.

6.2.2.- Watering from Below

Some plants have hairy, velvety leaves, where water droplets can become trapped by the hairs, acting like magnifying lenses under the light and resulting in scorch marks. Other plants have very fragile stems that can be damaged by the weight of the water. Others simply do not tolerate well getting their leaves too wet. And in some cases, the arrangements in the container, their pot or their voluptousness simply make difficult watering them from above. Orchids and bonsais, for instance, are often watered this way.

The technique for watering from below is immersion. We prepare a larger container with excess water inside, but never enough to go inside of the plant pot once it's submerged, or we'll make a mess. The only exception to this are plants using a growing medium made by large chunks, like orchids growing in large bark substrate.

Since the water will be sucked up by the drainage holes, we don't need to cover much of the pot. Having a few inches of water should be fine, but covering the pot one half of its height won't hurt either. You can always add more water if the plant drinks it all up. We leave the pot there for a few minutes. The precise time required would depend on the volume of substrate (smaller plant pots need less time soaking) and its composition and state, but in any case it's not convenient to let it sit there over half an hour. Then we take it out and let it drain for at least an hour, ideally hanging it so the drain water will not pool in the bottom.

If you are unsure about removing the plant from the water already or not, here's one easy way I have used to test it and make sure the immersion has been effective and the substrate is well wet. All you need is a thin bamboo stick. A wooden chopstick will probably do the trick too. You bury it in the soil carefully (and vertically) until it hits the bottom of the plant container, and leave it there for a couple minutes. Then you remove it, again carefully. If it brings along stuck substrate, or soil stains, the medium is already well hydrated and you can let the plant drain.

One advantage of watering this way is that you won't compact the substrate. One disadvantage is that, since you are in a way “washing” the lower part of the growing medium, it contributes in the long run to accumulate minerals in the upper third. So often, alternating above/below watering methods can be a good idea. Some people water by immersion when they are feeding the soil new nutrients (and when soil EC is low), and water from above otherwise (and when soil EC is high, to easy draining of the excess minerals).

The only other potential risk when watering by immersion is temperature shock, so you also want to make sure that the water is at a proper temperature for the roots. That's by default at ambient temperature, or lukewarm.

Watering by immersion is a good option to rehydrate the soil when it has become extremely dry. This can happen more easily in substrates heavily based in peat. When the soil becomes packed dry (when it visibly shrinks inside of the container and is not loose at all) it absorbs water very poorly, and even slow, thorough watering can leave behind pockets of packed dry soil. A way to fix this is submerging the pot inside of a container with water for a few minutes, then letting it drain thoroughly for a few hours, and check again in case the substrate needs another soak. As usual, make sure that the water does not overflow inside of the container.


There might be other unique, experimental, custom ways of delivering water to plants (and please do contribute with your watering tricks!!) but at the moment, we'll only talk a little about contingency watering - what to do when you have to leave your plants alone for some time.


6.2.3.- Auto-watering systems

Before anything, keep in mind that accumulated amounts of water in the base of the container should never stay there for a long time. Bacteria and fungus will make their home there and quickly colonize the substrate, and roots soaked or submerged will drown. Also, letting your plants suffer drought thinking that you will show up in the nick of time and then give them the deluge is not a good idea either. You might overestimate the time they will tolerate partial wilt and have a nasty surprise when you come back, or just stress them out unnecessarily and affect negatively their growth.

When we have to leave our plants unattended for a period longer than the usual gap between waterings, we need to use methods to make sure that the plants will get their water supply slowly and steadily, and/or to find ways to minimize water loss. I'm leaving here a little list of ideas.

- Humidifying plastic bags can be used for short periods of time (less than a week) in little plants that are okay with high humidity in their environment. Placing the plant inside of a clean transparent plastic bag will allow transpired water to condense on the sides of the bag and drip down, to be taken up again by the roots. You will need to make a few little holes in the bag to allow for gas renewal.

- Water retaining crystals can be used to cover the surface of the substrate whenever the frequency of watering is erratic, or to decrease water evaporation from soil. They absorb many times their own weight in water, hold it and release it back to the plants on demand.

- Capillary matting and wick watering systems are simple and can keep the soil hydrated for a few days. You can lay a capillary matting under the plant pots, and submerge one of the sides of the cloth in a water container. You can also bury a strip of capillary matting in the soil and leave the other end in a reservoir full with water, such as a plastic bag.

- Simple pump systems can fix your problem for a longer period. Besides commercial devices, you can make one yourself with a few parts: A wide container, a timer, an aquarium pump and plastic or rubber watering tubes. By fitting the watering tubes to the pump and plugging the pump to the timer you can make sure the plants will be fed regularly.


Thank you and see you in the next post about Atmosphere. Hopefully the long writeup hasn't scared you away this time

7 - The Atmosphere: Ventilation, Humidity and Temperature

Climate control, or atmosphere control, might be the most overlooked aspect of indoor gardening. Most particularly, if you intend to grow entheogens, a lot of species come from climates substantially different than the one you have at home. The air medium is the other end of the plant system; if you take care of what's below the plant, you should control what's around it.

There's three parameters in climate control. Air Flow, Humidity and Temperature. The three are tightly related to each other. They are interdependent.


7.1.- Ventilation

The air flow in the place where a plant is growing is absolutely essential. Proper ventilation will help to

- Refresh CO2 levels under the leaves, improving photosynthesis.
- Facilitate transpiration.
- Exercise the plant structure, encouraging strong stems and root systems.
- Assist temperature control.
- Lower ambient humidity when needed.
- Decrease the occurrence of diseases and rot problems.

Particularly if your indoor garden is inside of a closet, or in a little greenhouse, or simply in a place with little air renewal, you need to provide some air flow. The particular climate requirements of the species you are growing are important as always, but a little of air movement (just enough to gently move the leaves) will always contribute to remove the stale air below the leaf and keep it getting the most out of the nice light, balanced soil and careful watering you're undoubtedly giving her already.

In order to deliver air movement, there's two types of ventilation to consider. One aims to renew the air inside of the grow space. The other intends to keep the air inside of the grow space moving.

For air renewal, in the absence of natural ventilation, we have Intake and Exhaust fans. Intake fans pull air into the growing area, and exhaust fans push it out.

Since most growing spaces will have lights that radiate more or less heat, the air inside of the growing space will warm up. And since warm air ascends, it makes sense to place the intake fan in a low spot, so it will shoot fresh, cooler air towards the low parts of the plants, and the exhaust fan in a high spot, so it will push out the warm, “used” air. By simply placing the fans in distant, opposite places we direct air flow inside of the growing space.



If you were unable to place both (although it is recommended) extraction might be preferable, since at least it would facilitate some air renewal by suction, triggering a “passive” intake through holes in the lower part of the space. This is also the reason why it's a good idea to have a little bigger exhaustion power than intake power. Having more intake than exhaust power is generally a waste of energy.

For air movement, you can place one or several oscillating fans inside of the space itself. These will help to dissipate pockets of hot (or cold) air, making the atmosphere more uniform and giving all the leaves the same chance to do their magic. I have used little USB powered fans in small closets, a couple of them properly placed can be enough.

A third type of specific ventilation might be used to cool off lighting devices and ballasts, particularly in high-wattage systems. Classic indoor features involve a ventilation flexible pipe attached to the body of the ballast in one end and in an exhaustion fan in the other. There's commercial devices designed for this, like the Cooltube.

But keep in mind that ventilation is not only required when lights are on. In the first hours of darkness, good air replacement is great for preventing diseases like mildew or the botrytis fungus, whose spores like water condensation in the plant tissue to settle and thrive. Air flow keeps condensation from forming and helps keeping those away.

You can calculate the power you would need in both intake/exhaust fans and interior oscillating fans by measuring the volume of your growing space. Most commercial fans will be rated in the number of cubic meters, or cubic feet of air they can move per time unit. Say, for instance, that you have a gardening closet of 2x2x2 meters = 8 m3. If you wanted to renew all the air in the closet every 5 minutes (and that is a reasonable minimum, unless you are growing plants that like to be very still and humid), you would need intake/exhaust fans able to move 8 m3 x (60 min / 5 min) = 96 m3/hour.

Many different types and sizes of fans can be used for gardening, depending on the amount of space you have dedicated to growing and your particular needs. Small closets and terraria can use the ventilation provided by a couple of small computer fans, and large spaces might require a couple extractors and several oscillating fans to keep optimal air flow.

And remember a simple rule when adjusting your climate parameters:

Less ventilation > + humidity, + temperature
More ventilation > - humidity, - temperature


7.2.- Humidity and Temperature

As mentioned earlier, proper levels of humidity and temperature will allow the plant to function well, maintain healthy stems and leaves and stay well hydrated with less need to intervene. The frequency of watering needs to be higher if our growing space is hotter or drier than it should be.

We know temperature is a measure of heat, or the kinetic energy of the particles in a system, and humidity measures the amount of water vapor in the atmosphere. There is a close relationship between them, so it makes sense to discuss them together.

The higher the temperature, the higher the capacity of air to hold water vapor, and at the same time, the more heat it takes to raise the temperature yet another degree. When measuring humidity, we often talk about relative humidity. That is a percentile measure of the amount of water vapor present in the atmosphere regarding the maximum amount of water it can hold at that temperature. Which is to say, a volume of air at 50% humidity and 25 degrees Celsius holds more water than the same volume at also 50% humidity but only 15 degrees Celsius. We know that by experience, in the same humidity conditions the air feels dryer when it's cold. Most hygrometers (see below in 7.3) express relative humidity in their values, and the little fluctuations we might observe in closed grow spaces when we don't intervene directly in humidity levels are due to changes in temperature.

A plant's humidity requirements generally decrease with age. Seedlings and rooting clones welcome high humidity levels for as long as they cannot hold and gather enough water resources by themselves, while the ideal humidity levels for common blooming plants are around 40-50%. Too high humidity levels encourage diseases and decrease transpiration, and too low will dehydrate the plant and damage its structure by drying and facilitating spot burning and wilting under excess heat from the lights.

You can decrease humidity by increasing air flow, raising temperature or using a dehumidifier, and reversely increase humidity by decreasing air flow, lowering temperature or using some humidifier device. Besides commercial humidifiers, you can rely a little on cheap/contingency ways of increasing humidity levels inside of your growing space. That is, placing sources of water to increase the amount of vapor. You might place a little container with water in front of the intake fan, making sure that the water bottom doesn't sit there for too long, or hang a couple wet towels, or you can make a few cheap homemade humidifiers fitting wet (not waterlogged) sterile sponges inside of zip-lock bags with a few holes and placing them inside of your growing space.

Remember that high humidity can also be helpful when trying to bring a wilted or drought-stressed plant towards recovery. If you want to keep a plant inside of a humidity tent, you can use terraria, containers (keeping in mind the air renewal factor) or plastic bags, that will collect water vapor in their sides thanks to condensation and let it trickle down towards the base of the pot or the soil.

Regarding temperature, it will depend on the temperature of the incoming air (the external temperature), the amount of air circulation, and the heat load from your lights. As mentioned, temperature affects humidity levels and the hospitability of the environment for pests.

Speaking very generally, most plants will appreciate growing in a range of 18-26ºC (65-78ºF). Make sure that you check your plants requirements, this type of information is easy to find just by taking a look to the climate parameters in their native environments. Besides keeping the temperature in a balanced range, sudden changes of temperature should be generally avoided since they encourage pests and diseases. Our human immune system doesn't like sudden temperature shifts either. However, hardy plants and succulents acclimated to desert conditions will tolerate bigger temperature swings. The reason is that dry environments are much easier warmed up than humid environments (water is very efficient at absorbing heat) so the temperature difference between noon and night time can be much higher.



7.3.- Useful Gadgets for Environment Control

Other than the already mentioned fans for air movement, and all-purpose timers to schedule what goes on and off around the clock, several commercial devices can be useful for climate control when we cannot make our parameters fit the plants needs.

- Thermo Hygrometers.



This is your essential tool to measure temperature and humidity whenever you place the device or its sensor. Digital ones are affordable and often include features such as recording of maximum and minimum values, to allow monitoring the changes during the photoperiod. Even if you want to keep gardening simple, get one.

- Humidifiers.

Their range of prices and technologies is very wide, from simple, water deposit, portable humidifers to complex humidity controller stations. If you need to use one, just keep in mind that it should deliver cool humid air, not warm vapor.

- Thermostats and temperature control.

A thermostat is a device with a sensor that determines when it goes on and off according to temperature, activating either when it gets too cool (and then plugged to a heater, or already fitted to it) or when it gets too hot (with an AC unit). Some thermostats can work both ways, and you can find temperature control systems that can raise and lower temperature.

Thermostats can be also plugged to fans, triggering ventilation once temperature surpasses a certain level.


7.4.- An option: CO2 enrichment

Increasing the CO2 availability in the growing space, as long as good lighting and air flow are provided as well, can maximize the photosynthetic output of a plant. This is practiced when gardeners desire high yields and productivity in indoor gardens, and has been extensively used by cannabis indoor growers.

A homemade cheap source for a little CO2 boost can be done with a recipient with a small beaker, water, sugar and fresh baking yeast. Dissolve sugar in warm water until almost saturating it, and drop inside a little piece of the crumbled yeast. The bacteria will feast on the sugar and produce CO2 as a byproduct. Placing the container below the plants will feed them a little extra supply, but beware of uninvited guests like flies attracted to the sweet soup.

I think, though, that as long as you provide good air flow, lots of extra CO2 will easily become overkill, since there is a maximum of CO2 plants can use, but if you decide to provide CO2 enrichment, slightly higher temperatures can be maintained for an optimal rate of photosynthesis.


Thanks again for reading, I'll continue in the next post about Nutrients.

^Do you know if any study has been done boosting Nitrogen atmosphere levels? And how to, if so?
I ask because it's been suggested this may boost alkaloids in plants, either directly, or by boosting nitrogen fixing bacteria numbers.

Thanks again Vosdel for an awesome green read!

I'm not familiar with any studies about boosting atmosphere nitrogen. As you mention, nitrogen is fixated by bacteria in the soil, and since the percent of N2 in air is a whopping 78%, I doubt that raising inert N2 levels in the air beyond that would have any direct result in growth or alkaloid contents.

However, there are "natural" ways to increase the availability of nitrates (other than fertilizer supply) by increasing the presence of nitrogen fixation bacteria (rhizobium), ideally by growing in the same soil leguminous species like peas, soy or beans that have an optimal symbiotic relationship with rhizobium.

8. - Plant nutrition, I: The Mineral Nutrients


Besides light and the three non-mineral elements that plants need (hydrogen and oxygen from the water and the atmosphere, and carbon from CO2) they also require a variety of mineral nutrients performing several key functions. In their absence, the plant will lack essential metabolites and won't be able to complete properly a life cycle. We'll describe here which are those minerals, their functions and the most common symptoms in case of deficiency and excess.

Plant mineral nutrients have been traditionally divided (Justus Von Liebig, 1850) into three groups, according to their presence in plant tissue: Essential Macronutrients, Essential Micronutrients and other Beneficial Nutrients.

The normal, healthy state of the plant (or good pictures of a healthy specimen) should be your reference material in order to identify any problems with nutrient levels, both in excess and defect. Also, knowing the functions and specific details of each nutrient allows us to understand better the differences in nutrient defficiency symptoms. Some nutrients (N, P, K, Mg, Zn, Cl) are more easily transported within the plant from older plant parts to new growth spots such as younger leaves. Other nutrients (S, Ca, Fe, Cu, Mn, B) are not easily moved within the plant. That's why the deficiency of “mobile” elements is often expressed in older leaves first, and the deficiency of “non-mobile” elements appears in the active growing spots, as we'll detail now.


8.1.- Macronutrients

Macronutrients are essential minerals generally consumed in large amounts, and their presence in dry plant matter can range from 0,2% to over 4%. They serve basic biotic (protein building) and metabolic functions.

Three of them (Nitrogen (N), Phosporus (P) and Potassium (K)) are often referred to as “Primary Nutrients”, they eventually need to be replenished in long-term indoor gardening and they are always present in the common all-purpose NPK commercial fertilizers. The other three (Calcium (Ca), Magnesium (Mg) and Sulfur (S)) are usually called “Secondary Nutrients”, but even if a good soil mix will carry enough of them in the beginning, the problems in case of defficiency can be anything but secondary.


- Nitrogen (N).

Ionic Form: Nitrate NO3-, Ammonium NH4+
Relative mass to %N in plant matter: 100%
Functions: Essential brick for the synthesis of new amino acids, and hence all proteins and nucleic acids.
Common Sources: Nitrate and ammonium salts, urea, manure and animal waste, organic decay
Deficiency Symptoms: Yellowing of older leaves, overall leaves become paler. Long term defficiency will result in leaves falling. Slowed down growth.
Excess Symptoms: Dark green foliage, more susceptible to lodging, drought and pests. Most plant-feeding insects rely on nitrogen in their diet, so a nitrogen overdose will be a treat for them.
Notes: Nitrogen in the atmosphere cannot be generally used by plants, so it has to be converted to a fixed state. Outdoors, rain delivers nitrate and ammonium ions, and the plant leeches the rest of its nitrogen needs from soil sources, such as animal waste, decay or mineral deposits. Also, certain bacteria (Rhizobium) possess enzymes that can fix atmospheric nitrogen into chemically useful ions for the plants. When none of these factors is present in indoor gardening, you need to make sure that nitrogen in either ionic form is provided through soil add-ons or fertilization.


- Phosphorus (P)

Ionic Form: Phosphate H2PO4-
Average relative mass to %N in plant matter: 6%
Functions: Synthesis of nucleic acids and ATP.
Common Sources: Phosphate salts, bone fertilizers, greensand
Deficiency Symptoms: Stunted growth, delay in development. Leaf tips look burnt. Sometimes, purplish/reddish coloration in leaves (accumulation of the pigment anthocyanin), starting in the older leaves first. Reduced size in young leaves.
Excess Symptoms: Deficiency in micronutrients like Fe or Zn.


- Potassium (K)

Ionic Form: K+
Average relative mass to %N in plant matter: 25%
Functions: Catalyst and ions transport in plant metabolism.
Common Sources: Potash, potassium salts
Deficiency Symptoms: Margins of leaves yellowing and scorching, older leaves first. Severe defficiency will also brown the tissue between the leaf veins and produce irregular brown spots in leaves. Stunted growth.
Excess Symptoms: Deficiency in Mg and Ca.


- Sulphur (S)

Ionic Form: Sulphate SO4 2-
Average relative mass to %N in plant matter: 3%
Functions: Essential element for amino acid synthesis.
Common Sources: Sulphates, organic decay, epsom salts
Deficiency Symptoms: Yellowing in younger leaves, sometimes followed by older leaves. Symptoms are similar to N deficiency, but starting on new growth.
Excess Symptoms: Premature dropping of leaves.
Notes: Sulfur is usually found outdoors in sufficient amounts from the slow decomposition of soil organic matter. Supplemental use indoors is particularly important if you don't use any type of compost in your soil mix.


- Calcium (Ca)

Ionic Form: Ca 2+
Average relative mass to %N in plant matter: 12,5%
Functions: It's an essential element in the structure of plant cells.
Common sources: Lime, gypsum
Deficiency Symptoms: Stunted growth of plant and fruits, distortion and/or death of growing tips and blossoms. Specially problematic in young plants, where emerging leaves will show dead tissue areas along the leaf margins.
Excess Symptoms: Deficiency in Mg or K.
Notes: Generally large enough ammounts of Calcium are added when Lime is applied to acidic soils to raise pH. The double valency (2+) in Calcium ions is related to the degree of availability of the element in the soil; the higher the charge, the stronger the ions are bound to the soil and the less soluble they become, so it's recommended to supply Calcium in a slight excess. Too much Calcium, though, might raise excessively soil pH and negatively affect the uptake of other nutrients, particularly Magnesium, also a 2+ ion.


- Magnesium (Mg)

Ionic Form: Mg 2+
Relative mass to %N in plant matter: 8%
Functions: Chlorophyll composition.
Common Sources: Magnesium salts, like epsom salts.
Deficiency Symptoms: Interveinal chlorosis, a yellowing or bronzing of the leaf tissue between the veins, is a distinctive symptom of magnesium deficiency, starting in older leaves.
Excess Symptoms: High concentrations are generally well tolerated, but the imbalance with Ca and K may reduce growth.
Notes: As mentioned before, magnesium uptake can be negatively affected by large amounts of calcium.



8.2.- Micronutrients

These are elements essential for plant growth, but needed only in very small (micro) quantities, and often measured in p.p.m. (parts per million) amounts. The essential micronutrients are Iron, Zinc, Copper, Manganese, Boron, Molybdenum and Chlorine.

- Iron (Fe)
Ionic Form: Fe 2+, Fe 3+
Relative mass to %N in plant matter: 0,2%
Functions: Essential precursor for chlorophyll. Important functions in enzyme activity.
Deficiency Symptoms: Reduced green colour (less chlorophyll production) and interveinal chlorosis (yellowing of the areas between veins) particularly in new leaves. New leaves very pale or even white in extreme cases, leading to necrosis. Plant growth reduced.
Excess Symptoms: Possible bronzing of leaves with little brown-reddish spots, starting in young leaves.
Notes: The availability of iron gradually decreases with an increase of soil pH. Often this is referred to as “lime-induced chlorosis”.

- Zinc (Zn)
Ionic Form: Zn 2+
Relative mass to %N in plant matter: 0,03%
Functions: Enzyme activation element, function in the production of auxin (growth hormone)
Deficiency Symptoms: Smaller leaf size, shortening of internode lengths and interveinal yellowing/chlorosis in young leaves.
Excess Symptoms: Fe deficiency in some plants.

- Copper (Cu)
Ionic Form: Cu 2+
Relative mass to %N in plant matter: 0,01%
Functions: Carbohydrate and nitrogen metabolism. Essential in the synthesis of lignin, thus contributing to the overall strength and sturdiness of the plant.
Deficiency Symptoms: Stunted growth, weakness in stems and twigs, pale leaves that wither easily.
Excess Symptoms: Leaf chlorosis, often distributed unevenly, and stunted root growth.

- Manganese (Mn)
Ionic Form: Mn 2+
Relative mass to %N in plant matter: 0,1%
Functions: Enzyme activation element.
Deficiency Symptoms: Interveinal yellowing and mottling of young leaves. Reduction in the size of leaves, shoots and fruit. Dead spots can occur.
Excess Symptoms: Appearance of brown spots, often surrounded by a chlorotic (pale yellow) circle in older leaves.

- Boron (B)
Ionic Form: B(OH)3
Relative mass to %N in plant matter: 0,2%
Functions: Essential component in plant cell walls.
Deficiency Symptoms: Discoloration, deformation and/or death of growing tips. Growth can be stunted with very small terminal leaves, that eventually die and produce multiple budding below the dead terminal, giving a characteristic “Witches' broom” form. Seed and fruit production is significantly reduced.
Excess Symptoms: Leaf tips become yellow and scorched. Boron overdose will make leaves eventually fall off.

- Molybdenum (Mo)
Ionic Form: Molybdate MoO4 2-
Relative mass to %N in plant matter: 0,0001%
Functions: Participates in many enzymes responsible for nitrogen fixation.
Deficiency Symptoms: Mo is a highly mobile element, so its deficiency symptoms often appear on the entire plant. Similar to nitrogen deficiency, with yellowing of older leaves and the rest of the leaves becoming a paler green. The difference between both cases is more visible when Mo deficiency is extreme, leading to visible necrosis in the plant tissues, drastic reduction in leaf sizes and irregular leaf blade formation.
Excess Symptoms: Generally, plants tolerate well excess of Mo. However, concentrations higher than 500 ppm can be toxic in some plants, blocking Fe metabolism and resulting in the common symptoms for Fe deficiency.

- Chlorine (Cl)
Ionic Form: Chloride, Cl -
Relative mass to %N in plant matter: 0,3%
Functions: Required for optimal enzyme activity in photosynthetic reactions.
Deficiency Symptoms: Wilting of leaves, specially at the margins.
Excess Symptoms: Curling and scorching of the leaves.



8.3.- Other Beneficial Elements

Other minerals might have a positive effect in the plant development, although in the majority of cases they might be a boost, but not a requirement. Two arguable exceptions to this are Sodium and Nickel, so they come on top of the list. Cobalt also might have remarkable properties for entheogens gardeners.

- Sodium (Na)
Ionic Form: Na+
Function: Catalyst and ions transport in plant metabolism.
Notes: Traditionally not considered an essential nutrient, Sodium has very similar properties to Potassium and can serve the same functions, so to a certain extent it can act as a Potassium replacement regulating osmotic potential and metabolic activity. Be careful though, since an excess of sodium will inhibit the uptake of Potassium, Calcium and Magnesium, the cation (positive ion) macronutrients.

- Nickel (Ni)
Ionic Form: Ni 3+
Function: Allows nitrogen fixation under certain conditions.
Notes: The relatively recent discovery of Nickel as a component of urease, the enzyme capable of breaking down urea, makes this element an essential micro-nutrient when urea is used as the nitrogen source for plants. So for instance, if you are the type of gardener that would pee in your plants to feed them nitrogen, give them some nickel as well.

- Cobalt (Co)
Ionic Form: Cobalt chloride, CoCl2
Functions: In several plant species, cobalt retards aging, improves drought resistance and shows activity against certain molds and yeasts.
Notes: In some Solanaceae species like Datura Inoxia and Belladonna, the accumulation of alkaloids is regulated by Cobalt. This is an interesting property to research; Cobalt might be an useful aid in alkaloids boosting.

- Silicon (Si)
Ionic Form: Silicic Acid, Si(OH)4
Functions: Suppresses many plant diseases and insect attacks, protecting mechanically (by forming thickened silicon-cellulose membranes) the surface of the plant.

- Aluminium (Al)
Ionic Form: Al 3+
Functions: Low levels of Aluminum are known to stimulate root and shoot growth. Use carefully, since Aluminum can easily cross the boundary between beneficial and toxic effects.

- Selenium (Se)
Ionic Form: Selenite, SeO3 2-
Functions: It can act as a detoxifier, suppressing high concentrations of minerals and inhibiting the absorption of heavy metals.

- Vanadium (Va)
Ionic Form: Va 2+, Va 3+
Functions: It can work as a growth stimulant, particularly when iron or other metals are limiting.


That's all for now about the different mineral nutrients. In the next post, we'll quickly review the feeding process of the plants and discuss Fertilizers and their use. See you growers there.

Like I assumed, this is great. Learning so much new stuff. Thanks again Vodsel

Thanks to you Shaolin for the feedback

I do know this post can be useful, but since putting together the basic data from here and there is a little time consuming, I appreciate it.

I wish I had more spare time, I'll do my best to have all the contents initially covered by january.

And again, I encourage everyone to point out any mistakes and contribute with relevant bits I'm missing.

Learn, grow, expand

9.- Plant nutrition, II: Feeding plants. Fertilizers

In the previous post we talked about theory; now let's talk about practice.


9.1.- How plants feed

As mentioned before, plants acquire the mineral nutrients in dissolved form through their roots. More precisely, nutrient uptake in the soil is achieved by osmotic cation exchange. The mineral elements have to be dissolved into the water present in the soil in order to by taken by the root hairs.





The roots do not grow intentionally towards a nutrient source. Nutrient uptake requires that the individual nutrient ion be in adjacent position to the root. This positioning can occur by Root Interception (when the root literally bumps into the ion as it grows), Diffusion (the ion moves to the root balancing the different concentrations in the root and the soil solution) or Mass Flow (when the soluble fraction of the nutrients present in the soil water flow to the root as water is taken up by suction.

Different nutrients are taken up in different ways. N, S and Mg and principally acquired by mass flow, P and K are principally taken up by diffusion, and root interception fishes more often heavier elements like Ca and Mg.

As mentioned before, the soil pH strongly determines whether a mineral ion can be dissolved and available for the plant or will be stuck in the growing medium. Different pH ranges affect the availability of different mineral nutrients, and usually the optimal pH range for ion uptake sits roughly between 6 and 7.




9.2.- Types of Fertilizers

According to the origin of the mineral salts they provide, we can divide the fertilizers in two main categories: Organic and Inorganic.

Organic Fertilizers (OF) are naturally occurring fertilizers (peat, manure, seaweed, guano...), or products processed from materials of either plant or animal origin (blood/bone/fish meal, compost, natural aminoacids, extracts...)

Inorganic Fertilizers (IF) are either mined with little processing (lime, potash, phosphate rock...) or produced in industrial chemical processes (ammonia, sodium nitrates...). These are often also called Chemical Fertilizers.

According to their mechanism, we can divide fertilizers in Quick Release and Slow Release Fertilizers.

Quick Release Fertilizers (QRF) have generally high salt indexes, what makes them highly soluble in water and quickly available for the plant. They are more commonly found in liquid form, to be diluted in water.

These properties give them a higher burn potential, since they can alter dramatically the EC, the concentration of mineral ions in the growth medium, and hence there are major risks of over-fertilization when the nutrient levels are not monitored. For the same reasons, over-watering will wash nutrients away more easily. QRF require a more precise measuring and dosing of the nutrients, and overall lighter, more frequent fertilization. One advantage of QRF is that you can easily suspend feeding when the plant goes dormant in short-day / winter periods.

Slow Release fertilizers (SRF) carry nutrients in forms that are slowly soluble, slowly acquired by the medium, and/or held in a natural organic form that requires soil processes to be readily available for the roots to pick up. They are also called Controlled-Release fertilizers. Generally, SRF are either mixed with the soil when preparing it before planting, or added to the soil surface, and when processed they can be found in different forms such as powder, granules, pellets or spikes.

Plants are more tolerant to slight fertilization excesses with SRF, and since SRF have a long response effect they require less frequent application. However, and since the release rates of a SRF can be variable and depend on the properties of the soil you are using, keeping track of nutrient levels is also a good idea.

Sometimes OF are associated to SRF, and while it's true that a lot of them are released slowly, both are not synonymous.


9.3.- Feeding your plants

9.3.1.- Which Type of Fertilizer to Use?

Ok, so - What's better for indoor, Organic or Inorganic? Slow or Quick Release?

In outdoor gardening and agriculture, there's pros and cons for each type; outdoors, and when watering is irregular, QRF can cause big fluctuations in the soil EC levels (see 6.1.2), raising them a lot in drought periods and lowering them too much due to leaching when there's an excess of rain; outdoors, IF show larger pollutant risks when salts are leeched down.

Indoors, growing in a limited volume of substrate, the rules can be slightly different. Pollution is a smaller concern since the growing environment is isolated and the fertilizer amounts are smaller, and since the roots are developed within a limited space, you have reliable ways to measure the availability of nutrients in the substrate.

In general, we could say that IF act faster and are lighter, but are not as soil-friendly as OF and they have higher chances of burning the plant. Reversely, OF are generally acting slower and are more bulky, but it's usually harder to mess things up with them and they have a good synergy with the soil system. Besides these considerations, using either type of fertilizer depends on what you find and can afford, the particular cravings (if any) of the plants you're growing, and other factors such as:

- Watering Frequency. If your plants like a lot of water, or you water with abundant drainage, SRF might be a better choice since quick-released fertilizers will be more easily leached off the soil and wasted.
- Season. SRF will stay there for a longer time, and hence they are more suitable for the spring period to avoid accumulation of nutrients in winter time (presuming you have seasons in your indoor, that is).
- Ambient temperature. A warmer environment will increase the availability of nutrients, but at the same time increases the risks of over-fertilization.

And of course, whether you support more or less the origins and the manufacturing means of one fertilizer or another, should also be a reason for choosing.

An important thing to keep in mind is that a lot of OF rely on the presence of micro-organisms in the growing medium in order to be processed properly, so these should be avoided when growing plants in sterile, soil-less mediums, unless you use special supplements in the plants diet.

Personally, growing in soil, and unless the profile of the plant suggests otherwise, I like to add a 10% of worm castings or bat guano to the substrate mix (unless I'm using soil mix with an already high EC of 1,5+), and when nutrients need to be replenished I use liquid OF diluted in spring or distilled water, adjusting the fertilization frequency according to the EC readings of the soil.


9.3.2.- Different Fertilizers Commercially Available

The most common manufactured fertilizers in the market are concentrated liquids, quick release, either organic or inorganic, to be diluted (or dissolved, in the case of crystals or powder) in water, according to the proportions indicated in the label. Proportions are generally expressed in milliliters per liter, or in a factor like 1:250, for example. This means they recommend using one part of fertilizer per 250 parts of water, which equals 4 ml / l.

Basic information in nutrients bottles includes the N-P-K (Nitrogen-Phosphorous-Potassium) value, which expresses the proportions between the amounts of the three primary macro-nutrients present in the fertilizer. For instance, an N-P-K: 4-1-1 means there are four parts of nitrogen compounds for every part of phosphates and potassium.

The choice between different N-P-K values depends on the needs of every plant and particularly the stage of development. Foliage plants generally need more N and less K, while fruiting and flowering plants will appreciate a fair N-P-K balance, emphasizing on K as the buds are developing.

Also, most composite fertilizers include the basic amounts of other essential nutrients (often referred to as “essential trace elements”, like Fe, Mn, B, Cu, Mo or Zn. Often you will also find essential amino-acids, vitamins and certain enzymes and hormones to boost growth.

Foliage fertilization is an interesting technique to keep in mind. It consists in applying diluted fertilizer spraying directly onto the plant leaves. Lots of regular liquid fertilizers can be applied to the foliage as well. Foliage feeding can be a good alternate or supplemental method, since it increases the activity in the leaves, and then >> increases chlorophyll production and photosynthesis >> increases the need for water >> increases water uptake by the roots, which in turn increases the uptake of the nutrients present in the soil. When using foliage fertilization, and in cases where the leaves are meant to be eventually ingested, make sure that the ingredients in your fertilizer are food safe.

Other than the composite commercialized nutrients, I'm leaving here a fast reference list of traditionally used and interesting organic fertilizing compounds, their average nutrient concentration, their sources and their properties.

- Blood Meal (N-P-K:13-1-1, QRF) is dry animal blood, generally a cattle slaughterhouse by-product. It's used as an organic fertilizer with high Nitrogen concentration, either mixed in the potting soil or dissolved in water. It is very fast acting, so it can be applied to quickly fix nitrogen deficiency. The nitrogen salts in blood meal will decrease the soil pH, and a single application following the proportion indicated is usually sufficient for 6-8 weeks before subsequent feedings are needed.



- Bone meal (N-P-K: 4-12-0, SRF) is made from steamed and crushed animal bones, and it's particularly rich in phosphorous, carrying also a nitrogen supplement and a high amount of calcium. It has a slow release time due to its generally coarse texture. Bone meal has been traditionally appreciated for flowering plants and bulbs with high, immediate phosphorous needs, but if you want to give phosphates to your plant without risks of flooding the soil with excess phosphorous and calcium, using supplements like mycorrhizae (see below) might be a better idea.



- Fish liquid fertilizers (N-P-K: 5-1-1, QRF) are a good generic type of OF. They can be found in the form of fish emulsions or fish hydrolysates. The second are preferable since they keep better the oils, vitamines, enzymes and amino-acids in the original product. One downside of fish based fertilizers is their smell.



- Guano (variable N-P-K depending on the source, SRF/QRF) is the dry feces and urine of bats or seabirds. It's almost odorless when compared to horse or cattle manure, carries high nitrogen and phosphorous content and is often used as soil conditioner and fertilizer. It also has relevant fungicide properties and speeds up the decomposition processes in the soil. It's a flexible and effective fertilizer, and it can be applied directly into the soil mix or brewed, strained and added to the irrigation water. Arguably, the top quality in guano fertilizers is collected from desert bat caves, since dry climates keep the precious nitrates from being drained away by the rain.



- Earthworm Castings (SRF) are odorless and make a great addition to regular potting soils due to their rich levels of N,P,K and Ca. They also contain a high percentage of humus and humic acid (see below) for soil enrichment. Worm castings are a nice choice for mixing with non-fertilized soils, since they are helpful in preventing fungi and pathogens and their slow, steady release of nutrients is less likely to burn seedlings or weak re-potted plants.



- Seaweed Fertilizers (Variable, SRF/QRF) are obtained from seaweed like kelp or laminaria, and can be applied to your plants in the form of mulch or mixed in the water in the case of liquid seaweed OF. Both in soil preparation and feeding, seaweed fertilizers are a great alternative to blood meal if you ever want your plants to go vegan, and they are excellent products to use in foliar application. Considering they are complete and proven to have beneficial effects in almost every single aspect of the plant development, my money is on these in the long run.



- Alfalfa Meal (N-P-K: 2,5-1-1, QRF) is beneficial for both the plant and the soil micro-organisms, since it includes carbohydrates and proteins from the alfalfa plant. Alfalfa is high in aminoacids, vitamins, plus N-P-K, Ca, Mg and other essential nutrients. Within the right proportions, it's a good growing boost and increases the plants tolerance to cold. Some gardeners use alfalfa tea as a foliar fertilizer.



Besides fertilizers, other supplements can be used to increase their efficiency transforming insoluble nutrients into usable ones and enhancing the activity of beneficial micro-organisms in the soil. There's many manufactured products with enzymes, amino-acids and other compounds for that purpose. Some ideas to consider include:

- Humic Acid, a major constituent of soil compost, is a mixture of different acids and can be regarded as humus liquid extract. It is often found as an ingredient in booster mixes or as a product by itself, and it can be a cost-effective way to improve poor soils and activate the roots metabolism and the uptake of nutrients.
- Nettle leaves can be brewed or soaked in water for a few days and pressed to obtain a concentrated solution very beneficial for gardens. Besides providing a rich supply of minerals, nettle speeds up the decomposition processes in the soil and helps to prevent pests, molds and fungi. We'll talk further about nettle in the chapter about Pests & Diseases.
- Mycorrhizal Fungi form a symbiotic relationship with plant roots, colonizing them with mycelium and boosting the availability and uptake of phosphorous. Micorrhizae are very estimated in organic gardening, and they can be very beneficial when added in supplemental amounts for good root development. They are often present in root stimulation mixes.


9.4.- Some Tips on Fertilizing

- Know the water you are using. Light mineral water, for instance, usually provides Mg, S, Ca, Cl and Na. Many fertilizing preparations include the minerals not commonly present in spring or tap water, so with a little research and label reading you can easily cross out in the list all the required nutrients for your plants health.

- Unlike moisture, nutrient availability is not easy to check. Since the only external indicator is the plant itself and seeing visible symptoms of nutrient deficiency or excess is not good news, it's important to be careful and the best way to be careful is measuring the EC of the soil when watering. As a rule of thumb, I try to keep the soil EC (measured in drained water) around 1,5. If you cannot or won't check the EC, at least keep track in a calendar of the times you have fed the plant and try to following the suggestions of the product you are using. And when using soil mixes for growing, unless you detect a deficiency, avoid fertilizing in the two months after planting or re-potting a plant in fresh soil.

- Fertilization is more necessary in the growing seasons. Few plants need fertilizer in the winter months.

- Never, never fertilize when the substrate has become dry. Rehydrate it first, and once the plant has recovered from drought you can feed it. If you fertilize when rehydrating the substrate, chances of indigestion by over-fertilization are much higher.

- If possible, fertilize early in the morning/beginning of the light period, and the evening/end of the light period would be the second choice. This is to prevent and excessive uptake of nutrients by the plant in peak photosynthetic activity.

- Keep your fertilizers in a cool, dark, dry place to prevent degradation. Particularly in the case of OF.

- To treat nutrient excess, the most common method involves washing the roots by immersion watering (see 6.2.2). You could also water profusely without submerging the plant, using three times the volume of substrate in water. Remember that often symptoms of excess and deficiency of several nutrients can be similar. When in doubt, flushing the soil with the methods mentioned before, letting drain well and restoring the pH and nutrient values with proper fertilization is always a good idea.

- In gardening books and websites, it's not uncommon to read advice to use an amount of fertilizer a little below the suggestion of the manufacturer. Although some sellers might overstate the amount of product to be used, moderation is basically suggested because most people is already using soil with a significant nutrient value, and amateur gardeners are more prone to over-fertilize than under-fertilize once they got a fancy nutrients bottle.


At the moment, this is all about nutrients and feeding the plant. As always, contributions and debugging are more than welcome. In the next post, we'll start to discuss the stages of plant development starting with the seed.

Thanks for reading

10 - Seeds and Germination


There's two basic ways of starting a plant: by propagation (using cuttings from an established mother plant, either stem, leaf or root depending on the species) and by germination, from seed. Some seeds can be easy to germinate right away (like cannabis or syrian rue), others require some previous treatment (like most mimosas and acacias), and others can be seldom viable (like salvia divinorum). Finally, some plants like ferns and mosses produce no flowers and reproduce by different methods.

In either case, and when possible, growing a plant from seed is very rewarding, and allows the gardener to become familiar with the morphology and each of the growth stages of the species. That can prove extremely useful when the plant is developing steadily and we intend to shape or control its growth. Also, and unlike plants grown from cuttings, which are clones of the mother plant, plants grown from seed may display different characteristics of ancestors going back several generations, giving the gardener a chance to perform selections according to traits in the seedlings.



In this post I'll leave some basic information about seeds, describe the most common effective ways of germinating them and give a few hints to grow healthy seedlings. Remember that a plant is a living process, and as such, the beginning strongly determines the rest.


10.1. – Basic Seed Morphology

Think of plant fruits as mature ovaries, containing seeds. And a seed contains the embryo of a plant. It's a fertilized and ripened ovule with genes of both the male and the female parents.

Plants that propagate by seed are divided in two categories, gymnosperms (conifers and related groups, around 750 species) and angiosperms (flowering plants, around a quarter million of species). The information provided in this post refers to typical flowering plants.

Seeds are very diverse in size and shape. Strawberry or mustard seeds are tiny specks, and an avocado seed can be the size of an egg. To take a look at the basic components of a seed, no matter its size and form, we're using this image of a common dicotyledon (a plant with two cotyledons):



What we call seed coat is the protective outer layer, and it protects the endosperm (temporal nutrient storage provided by the mother plant, to use until the seed develops means to make its own food) and the plant embryo itself.

A mature embryo consists of one or more cotyledons (the seed leaves you will see peeking first after germination), the hypocotyl (embryonic stem below the cotyledons) and the radicle or embryonic root.

The hilum, or “eye”, is the scar left on the seed coat marking the point where the seed was attached to the mother plant tissue. The micropyle is a little hole in the coat, through which pollen usually passes in fertilization. Later it often becomes the main entry point for water, which is the main factor to induce seed germination.

Some types of mature seeds contain other distinctive parts, such as a perisperm, while others have already consumed the endosperm when ripe. If you want further general information about types, morphology and evolution of seed forms, this is a good place to start.


10.2. – Germinating Seeds

Germination is the process by which the plant embryo inside of the seed develops into a plant seedling. The main factor in germination is the absorption of water by the embryo, which reactivates its metabolic system, and for this to occur we have three requirements: The seed has to be viable, the seed has to be out of its dormancy period if any, and the environment has to be the appropriate.


10.2.1. - Seed Viability

For a seed to be viable, it has to be functional. Non-viable seeds include seeds that were born with an incomplete embryo or without one at all, seeds that have dried excessively, rotted due to the action of pathogens in excess humidity, been attacked by predators, or simply aged too much. Remember that an embryo is living tissue, living cells keep dying and eventually they cannot be replaced anymore.

The germination percentage describes the statistical proportion of seeds that germinate from all the seeds planted or sowed, in proper growth conditions. It's an experimental measure you can make with each seed stock you have or, when you know the germination percentage already, it hints you the number of seeds you'll need in order to obtain roughly X plant seedlings.

The germination rate is the time it takes for the seed to become a seedling. This time may be significantly increased by low seed viability and non-optimal growth conditions. Generally, fresh seeds have the lowest germination rates, that keep rising as the seed ages.


10.2.2.- Seed Dormancy

Some seeds may go dormant, entering a state where germination will not happen in the conditions that would otherwise trigger germination. Many plant species can produce seeds that delay germination for a long period of time for ecological or physical reasons. The seed coat might be hard or impermeable, certain chemical changes in the embryo might be necessary prior to germination, the seed might require light exposure or a higher temperature than usual, or the embryo might need further maturing to become fully viable.


10.2.3.- Seed Treatments

Before placing the seed in the growing medium, previous seed treatment may be necessary for seeds that have a low viability, or dormant seeds, or simply to increase the germination percentage – specially with old or lowly permeable seeds. The more you know about the particularities of the seeds you intend to grow, including how long they have been stored and in which conditions, the easier it will be to successfully choose and apply these methods.

- Scarification is often used to ease the penetration of water into the seed. Some families of seeds (i.e. solanaceae) might have hard seed coats, or the seeds you're using might have a low germination percentage and you want to give them an extra push. By scarifying you thin the seed coat or remove a part of it, increasing or allowing the absorption of water by the embryo. There's several ways to do this depending on the size and type of seed. You could use a sharp knife, scissors or a nail cutter to carefully remove a little fragment of the seed coat (trying no to harm the hilum and of course the embryo if possible) or you could file the seed coat. Some people use a match box with a piece of sandpaper inside, put there the seed and shake the box for a minute. I personally prefer little sharp scissors or a nail cutter, sterilizing them before cutting to ensure they are free of pathogens.

After scarifying the seed, or when the seeds are too small for scarification, or simply when scarification is not required, the most common procedure is...

- Soaking the seed. It often reduces significantly the time required for germination by softening the seed coat, and/or by hydrating the embryo. Also, some seeds have chemical inhibitors in the coat that can be washed soaking the seed. The soaking can be performed until the radicle starts to peek out of the seed, until the seed visibly swells, or until the coat has changed to a clearer color. This can be done in multiple ways, more or less pushy.

A gentle and effective way requires a shallow plate and paper tissues. Place a folded tissue bed in the bottom of the plate, soak it with slight excess of water, place the seeds on it, and cover the seeds by a couple double-folded, also wet paper tissues. Keep in a warm, dark place. Many seeds will start germination in one or two days, you can easily check lifting the upper paper layer. This method is often used for cannabis seeds. Once half an inch of the radicle has come out of any seeds, they are ready to be planted.

You can also soak the seeds in excess water, inside of a little container. This method should not be used for longer than one day (at least, not without renewing the water) to avoid chances of bacteria developing in stained water, or the water running out of oxygen for the seed. After 24 hours, seeds that look swollen, visibly clearer or with hints of the radicle coming out can be planted, and the rest re-treated for a second day with fresh water.

It is highly recommended to use clean water, preferably with a low EC. Distilled water and spring water with low mineral content are the most suitable, and it's a good idea to sterilize it, boiling it before use. Tough-coated seeds might be softened when soaked in water just boiled, letting the water cool off as the seeds soak. In any case, do NOT boil the seeds, as it will most likely kill them.

- A stronger chemical wash of the seed can be required in the case of seeds held dormant by non water soluble substances in the coat, or when thorough sterilization of the seed seems desirable. A simple wash can be done in distilled/deionized water with a 5% bleach or hydrogen peroxide solution, for about 10-15 minutes. Seeds should then be well rinsed with clean water before planting or further soaking.

Needless to say, this should not be performed once the seed coat has been permeabilized by scarification or soaking, unless we want to damage the embryo tissue. In some cases you might combine the soaking and washing, by adding a few drops of peroxide to the soaking water.

- Use of Gibberellic Acid, a hormone promoting cell growth, is indicated in the case of many dormant seeds. It usually comes in powder form, and is applied by soaking the seed in water with dissolved GA in a concentration of around 2,000 ppm (parts per million) which equals approximately 500 mg GA per cup of water.

- Cold Stratification. For seeds with dormant or immature embryos, a period of chilling may be required to enable germination. Some seeds like winter and actually become dormant when exposed to temperatures over 20-25ºC, and they require cold to enter the germination stage. Think of it as keeping the seeds in moist/cold season conditions so they show up by the beginning of spring time.

To stratify seeds indoors, you can mix them with a little of moistened, sterile medium inside of a ziplock bag and then store it in your refrigerator (or even freezer, in certain species) for the required time, usually 2-4 weeks.

- Continuous High Temperature (around the range of 30ºC) may be needed to activate certain summer-loving seeds before they are able to germinate.

- Exposure to light. Some types of seeds, like poppy seeds, are “enabled” (waken up from dormancy) when exposed to continuous light for a certain period of time. This, as the use of higher temperatures, is quite specific.

Please note that the two last methods are generally applied when the seed is already placed in the growing substrate.


10.2.4.- Planting the Seed

Once the seed has been treated in any necessary ways, you should place it in your growing medium of choice.

The container can be either an individual small plastic pot, a hydrated jiffy peat pellet or a dedicated germination tray. If you use a container, and unless you are planting a species that resists transplanting, pick a small one (6 inches maximum) since it's easier to obtain properly developed roots in small pots, then transplant. Germination trays may require careful transplanting of the seedlings once they are developed, but are useful for larger amounts of small seed with low germination percentages, or to avoid handling a lot of separate small containers. Avoid open, non-compartmentalized trays deeper than three inches. In any case, good drainage holes are essential. If your container or tray doesn't have enough drainage holes, punch some in. You could also use special containers for air pruning (see 10.5).



The chosen substrate should have excellent aeration and draining capabilities, as well as good water retention properties. Options are perlite, vermiculite, coconut fiber (or other fine textured bark) and peat, or a mix of either. There's also good seed starting mixes available commercially. Remember that, whichever substrate you use, it should be spongy and moist. For more details, refer to the chapter about Substrates.

The way of planting the seeds varies. Cacti and other succulents seeds are often sown in the surface of the soil, and lightly covered with a thin layer of sandy potting mix; other seeds will require being exposed to light. Most of them, though, should be placed inside of a previously prepared hole in the growing medium. A good rule of thumb for the planting depth is 1-2 times the size of the seed. The seed should be placed gently inside of the hole, without pushing, and if the radicle is already visible it should be pointing downwards/sideways (depending on the plant) to spare the seed unnecessary effort. Then the hole can be covered with soil and the surface misted if necessary.

You will need to provide high humidity levels for the seed to finish germination. You can place a plastic wrap covering the pot, held with a rubber band, or place a plastic dome over it. Transparent plastic bottles cut in half make decent improvised humidity domes, plus you can use the bottle lid to regulate air exchange. Germination trays usually come with a lid, often with plastic shutters that can be adjusted according to the level of ventilation required. If you use a pot with a tight plastic wrap, poke a few tiny holes with a needle after the first days, or when required, to allow for a little air renewal. When using containers, I prefer using plastic domes (or placing the pots inside of a germination tray with its own large lid) because filling the containers to their whole capacity, leveling the potting mix even with the top, allows for good flow of air in the surface and discourages disease. Lots of molds thrive more easily in the pockets of static air.

Finally, some seeds will like some under-heating for germination. If you place a heating mat below your germinating plants, make sure it's in a low setting and preferably keep a gap between the mat and the germination tray to let the air move and to avoid over-heating.



10.3.- Seedling Care

Once the cotyledons unfold in the surface, or the cactus stem peeks out, and until the plant is well established and able to develop with the standard environmental conditions for its species, we have a seedling. Seedlings are deploying the plant machinery – roots, stem and leaves. They are still very sensitive to harsh conditions and diseases, so you should check on them daily and take special care of their growing conditions in this stage.

10.3.1.- Light and temperature

Plants that just came out to light prefer soft lighting, and medium/warm temperatures. Direct sunlight will easily kill them. When growing indoors, the safe distance between a seedling and your lights depends on the plant's tolerance of light intensity and heat. When heat is not an issue (and that's why fluorescent tubes make great lamps for seed germination) seedlings will get the most out of lights when placed three or four inches below them. Think ahead of ways to adjust the height of the lights (pulleys, chains, straps...) as your seedlings grow.

10.3.2.- Humidity and Watering

Damping off is the most common cause of death for a seedling. Seedlings growing apparently fine fall over suddenly and die for no apparent reason. This can be caused by different types of fungi, and that's why using a sterile soil is particularly important when growing from seed, since fungi love wet substrates and you cannot allow your seedlings to dry out.

Balance and daily care is key. Never allow the substrate to dry completely at this stage. The plant has a small root system, and barely any water storage capabilities yet, and it will not survive severe water shortage. Keeping the medium moist by regular light watering is required, specially when you need to remove any plastic wraps or domes you placed to maintain good humidity levels, once the seedling outgrows them. Any changes in humidity levels should be as progressive as possible, to avoid stress and the drying of plant tissue.

When watering, make sure that you water enough for the whole medium to become moist; if the water only reaches the surface, the roots will not develop properly, so either make sure that a little water drains down the container holes, or water your seedlings from below. No water should remain pooled under the seedlings afterwards. Also, if watering from top, water by misting to avoid compacting the medium with the weight and flow of the water.

Unless you are using a soilless medium without nutrients like perlite, seedlings do not require fertilization. Usually, new plants should not be fertilized until they are at least two months old.



10.4.– Seed Storage

And how can you keep the seeds you are not germinating right away? When properly preserved, lots of seeds can remain viable for quite a long time. Besides extreme cases (lotus seeds, for instance, have been known to germinate after centuries), many seeds will store well for a couple years when kept in an environment that does not favor plant metabolism and keeps away bacteria and molds. That means clean containers in a cool, dry, dark place. Placing them in labeled zip-lock bags inside of an airtight container in the fridge is an easy and practical option.

Keep in mind that some seeds, such as most passiflora species, simply will not be well preserved, and won't be viable no matter what you do. Be careful when acquiring seeds of species that have a short shelf life. If they're not fresh, they will be only useful as they are often labeled: incense, beads or botanical specimen.


10.5.-Air Pruning – Contribution by wearepeople

Air pruning is a method which aims to help plants develop full, well-balanced root structures during germination. When the roots grow through the soil and start poking out into the air, the tip of the root dies, then quickly heals over. This makes the root branch inside the soil.

The main advantage of air pruning is that when it comes time to transplant the seedling to a larger pot, the roots are developed in a way that will help them adjust to the new soil. With a fully developed root structure, seedlings can quickly disperse new roots into the medium, greatly improving their chances of surviving.

When standard pots or cups are used for germination, root problems often develop. A well developed root structure has a main tap root with many branches.

10.4.1.- Options for air pruning

- Specialized Pots
The basic design is one that includes large area of exposed soil on the sides and bottom of the pot. Air pruning pots come in a variety of shapes, sizes and nuances.

- Peat Moss Pellets
Peat moss discs are an inexpensive alternative to specialized air pruning pots. They are sold as compact, dried discs for about $0.20 (USD) each (there are smaller peat pellets for 5 or 10 cents each). When ready to use, place the disc in a bowl of water and it will expand to its full size in about 10 minutes. The peat moss is held together by a thin net. This net acts as a pot and helps the peat moss keep cylindrical form.

Jiffy, a manufacturer of these pellets, includes fertilizer in their pellets and the pH is about 5.3. They are also very easy to transplant. I recommend removing the net from the peat moss before transplanting if it can be done with little harm to the roots. If the net cannot be easily removed, you can make a few cuts in it with scissors and further root development will do the job of bursting open the net.

Jiffy also makes a peat-moss-free version which is made from coconut industry waste. (Coconut fiber has excellent draining and aeration properties, so this version may be indicated for seeds that have long germination times, and hence higher risk of molds due to compaction, sustained water saturation and low ventilation.)

- Rockwool Blocks. See post about Substrates for some info about rockwool.
- Homemade Fabric Bags.
- Woven Bags (designed for air pruning)


The purpose of air pruning is to facilitate proper root development for re-potting. We'll cover transplanting in the next post, along with other techniques for growth control.

Have a great Christmas/Yule/Hannukah/Whatever, and See you guys there

Vosdel, amazing work!

Thank you.

Thanks to you for your help, really appreciated

great info on micro nutrients

i am learning lots

awesome informative post!

I love this thread this much <-------------------------------------------------------------------------------------->

I have learned so much and since I live in an apartment, indoor grow is my only option. Awesome work Vodsel, thank you

Thank you, biopsylo, boogerz and Miksiton I'm glad it's turning out useful for you. Next post will be online soon.

Please let me know if you find any omissions or mistakes, or if you want to contribute with anything of your own.

11 - Growth Control I: Transplanting


Following your plants and intervening whenever needed to make sure they develop properly is the bread and butter of gardening. And when gardening indoors, growth control is even more important since resources like growing space and light are limited. With some basic knowledge and a little attention you can guarantee your plants will make the best out of the resources you have.


11.1. - About Transplanting

If you want a plant to keep growing, root growth is the first requirement. Longer and stronger roots will support more weight, and will be able to deliver a bigger flow of water and nutrients to the stem and leaves. Roots keep digging and exploring, and will eventually build an exhaustive network across the whole substrate volume. When that happens, the soil will dry faster, nutrients will be depleted faster and the development of the plant will come to a halt. Of course, you might want to simply sustain the plant in that stage, you might have run out of room and decide to harvest the whole plant in that moment (and perhaps take cuttings) but most of the times you want the plant to keep growing and get stronger. Then you need to give the plant more room and additional substrate.

In any case, there's going to be at least one time where potting up is due - if you're growing from seed, in order to move the seedling from the little germination container, or the germination tray, to a proper container for its full growth. Some people may decide they want to save efforts and directly place the seedling in the largest container they have as definitive home, but gradual potting up contributes greatly to a strong, uniform root development, and also gives the gardener a chance to take a look to the root system and improve it.




11.2.- When should you transplant?

There's a few symptoms that make good reasons. Roots clearly protruding from the drainage holes in the bottom of the pot, roots tightly bound to the container shape, alterations in the soil (like too low water retention and slow absorption), or the simple fact the plant seems to have stopped growing for no other apparent reason. Either of these should get you ready for re-potting, or potting up.

Any procedure that might momentarily stress the plant should be performed, if possible, in a moment when the plant will have plenty of resources and energy to invest in recovery. For plants grown outdoors, that usually means in early spring or summer; indoors, with plants in vegetative growing stage, and unless we are reproducing an annual light period in our indoor garden, we might transplant any time. Ideally, when the temperature is not too low, or abnormally high. As a common sense rule, leave always enough time for the plant to recover after stress. Other moments to avoid messing with the plant are the flowering and fruiting stages. So if you ever intend to induce flowering by alteration of the photo-period, try to transplant at least a week before changing it.

But if for some reason re-potting is an emergency, you can disregard timing issues and do it right away. The plant will be able to handle it.


11.3.- Re-potting procedure

If the plant is well root-bound to the pot, you should water well a couple days before, so the soil will be slightly moist when transplanting. It will make the process easier and gentler to the roots. But if the plant is not root-bound, wait to move it when the soil is rather dry. If the soil is moist and loose, and no roots are grabbing it tight, you might make a mess when trying to move out the plant and the roots will be more exposed to damage in the process.

When potting up, you have to prepare in advance a clean container with proper drainage holes, about two or three inches wider than the previous pot (unless you only intend to refresh the soil, without changing the container, by root pruning - see below). Always consider the potential needs and growth rate of the species you are growing, but when in doubt, pick the larger container. Some sources suggest to put a base of “drainage” material in the bottom of the pot (pieces of bark, expanded clay pellets, pebbles, crockery pieces...) so there you'd have a chance to do that, but unless that's explicitly good for your plant for some reason, you are better off using all the precious volume in your pot with useful medium and skipping that bottom layer. Drainage actually works better with the soil evenly filling the container.

Remember to use fresh soil, with adequate properties and pH value, and filling up as much as you need. You can measure previously the height of the old container to figure out the required depth.

There might be reasons, however, to leave a different depth than the height of the previous container. Some plants, loving moisture, may like to be planted a little deeper into the soil, keeping their roots away from the dryness of the surface. Others, more vulnerable to root rot like certain succulents and bulbs, might prefer to be placed a little higher than the ground level. Also, you may need to prune the base of the root ball or remove part of the old soil below it. By default, when filling up the new container you should aim for leveling, or half an inch lower than that, so a little layer of fresh soil can be added on top once the plant is there. In general, we don't want the old soil to protrude because that will increase water loss by evaporation.

Water the new soil well before placing the plant, preferably with lukewarm water. Our first priority now is root development, we need to encourage the roots to dig into the new territory, and moist soil will tease them out. So water the soil until it is thoroughly moist, adding any desired compounds in the irrigation mix if necessary. This is the ideal moment to add supplements like mycorrhizae (symbiotic fungus for the roots) or slow release fertilizers in the new soil.

Once the destination is ready, we can remove the plant from its tight home. This is usually done by tipping it from its pot.

It the roots have come out of the drainage holes and are entangled, you need to release them first. Some may need to be cut, or simply pinched with your fingers, or gently pushed inside with a pencil. Once the roots are free, you may want to slide carefully a knife around the inside of the pot if you don't feel the plant loose enough. Then you can slip one hand over the top of the pot (usually holding the main stem between your fingers, cupping slightly) and invert the pot with the other hand. If it doesn't come down right away, a bit of squeezing or a few firm taps against the bottom or the sides of the container should release it, so it rests upside down on the palm of your hand. In the worst case, if nothing seems to release the plant, you can always break or cut the old container.

Then it's the best moment to take a good look to the root ball and fix any problems before placing the plant in its new place. This is the moment for a procedure that can be a reason itself for re-potting: root pruning.



When a plant is already mature size, or when you don't have room for the plant to grow any larger, you still should re-pot the plant once a year so you can remove packed roots, loosen the root ball a bit and obtain an extra growth flush. And whether the plant is fully grown or not, pruning dead or damaged roots will always help in the next growing stage.

Use clean scissors, and look for any dead, dry roots and trim them. If the bottom looks like a thick root mass, you can cut it right away. Don't hesitate in cutting the whole thick lower third of root mass in plants that haven't been re-potted in a long time. If you find circular root patterns in the bottom, cut them. These are roots looking for air that might strangle the whole root system. If the walls of the container have a thick layer of roots, you can untangle it with your fingers or peel it right away with a knife. When necessary, don't be afraid of pruning excessively packed roots as long as you leave the central root mass intact.

But even if you don't think root pruning is necessary, if the plant was root bound, gently tease out the packed roots around the soil, so they point outwards. This will help them grow faster into the new medium, and the faster the roots stabilize, the earlier the plant will resume full growth.

Once the root ball looks good, you can adjust the soil level in the new container if needed and place the plant well centered on top. Then fill the space around the root ball with more soil mix. Avoid stuffing it unless your plant loves packed soil, remember the general guidelines for potting. You can gently squeeze it (specially if you happen to be straightening up the plant stem as you transplant, and need an extra support in the ground) but simply filling it and tapping the container against a surface a few times will leave it nice and spongy. If after a couple waterings the soil becomes more compacted and sinks, you can always add some more fresh soil as filler.


11.4.- A few notes about moving seedlings

If you started your plants from seed, the way to move them safely to their first house depends on the way of germination. Seeds started in small pots might stay a little longer before moving, but waiting until the young plant is root bound might stunt its growth. Usually waiting until a few roots show up through the drainage holes will suffice. Then you can let the substrate dry out a reasonable amount and tip the seedling from its pot, following the mentioned procedure.

When seeds were started in a germination tray, and of course also considering the particularities of the species, you should move them a little earlier, before the roots expand too much and become entangled. You can pick up the plants carefully digging around their spot and picking a large spoonful of moist soil including the plant and the roots. Make sure you don't use tools that might easily cut the root feeders, a couple wooden spoons make great tools for fishing out seedlings. If you need to pick up the plant itself for any reason in order to place it in the new container, avoid touching the roots and the fragile stem and pick it up gently by the leaves.

If you used hydrated peat pellets for germination, moving seedlings is very easy since you don't even have to touch the plant. If you want, you can make carefully a few little cuts in the sides of the net before placing it in its new home, to ease root expansion. Other than that, it's recommended to bury the whole peat pellet so the net rim won't act like a wick and cause excess soil moisture to evaporate.

In any case, and since the vertical space is limited in an indoor garden, you can bury seedlings up to right below the cotyledons to gain a couple inches of space under the growing light. Just don't leave the leaves too close (touching) the substrate, to avoid rot problems.

Once your plant is in the new pot, you can water it again if you think it's necessary. I usually water generously the new soil and leave the old one slightly moist. Besides that, make sure that the plant has comfy days ahead. And remember that keeping the ground level close to the rim of the container facilitates ventilation, so feel free to top it with some extra soil to make it even.

If you have seriously pruned the roots, don't be cheap with water and trim the plant's foliage according to how much the roots have been pruned, removing an equivalent proportion from the top growth. New root growth will bring new shoots; to understand better how to cut stems or leaves and why, we'll talk in the next post about pruning.

Thanks for reading and see you guys there.

..awesome thread let me say again Vosdel..very helpful!

i'm curious if anyone has experimented with use of root-node bacteria (rhyzobium) indoors (as this greatly aids legume/acacia growth)
..also wondering if any indoor growers here have used pro-active microbes in indoor growing..i know of various pro-microbe liquid formulas available from some plant-tech firms..
i'm used to the concept of hydroponic growers eliminating all microbes, but i know very little about how they can be harnessed effectively indoors..like in permaculture gardening where 'nitrogen fixers' are a staple..
.

I haven't tried myself specific bio-fertilizers with rhizobium bacteria (yet), so I endorse nen's question.

Rhizobium Etli seems to be the most utilized species, in available forms with 5x10^8 bacteria per gram, so a seedling could be inoculated with around 200mg of fertilizer.

And for the record, acacias are symbiotically associated with particular Rhizobium species, like Mesorhizobium Plurifarium, and some newly found Sinorhizobium (Arboris, Kostiense and Terangae - source, in spanish).

I have tried, though, bio-fertilizers with mycorrhizae fungi, and they certainly speed up the growth in leafy plants. I'm not sure if they have any effect in alkaloid-terpenoid contents.

12 - Growth Control, II: Pruning and Training


12.1.- Pruning

Cutting selectively stems and/or leaves of your plants is an extremely versatile procedure. Most people relate pruning to the process of shearing a topiary in the garden, but it goes much further than simply shaping the contour of a plant. Some of the multiple reasons to prune are:

- Directing the growth of the plant.
- Keeping stems from rubbing or crossing excessively.
- Promoting flowering or fruiting.
- Cleaning dead stems and clearing up the main body of the plant.
- Acquiring cuttings for propagation.
- Reducing the mass and surface of the plant after pruning the roots.
- Removing diseased or damaged stems.
- Preventing rot and fungus.

Besides the last two listed, note that the rest of points have to do with the proper growth and development of the plant. And as in other aspects, gardening indoors brings the opportunity along with the challenge. You have limited resources, and you have to provide for everything; but as you do that, you can make sure the plant is using those resources optimally, and have it develop the way you prefer considering the available space and the reasons why you are growing the plant.

You might be growing aloe or cacti for propagation and grafting, or salvia for the leaves, or silene capensis for the roots, or acacias for the phyllodes, or cannabis for the flowers. In either case, each purpose and each plant will have an ideal pace and structure, and pruning is an awesome tool to get the most out of the growing space you constructed.

All this requires learning a little about how your plant grows. Giving details about how different families or specific plants develop exceeds the scope of this thread, but an overall idea will be useful no matter what you're growing. Also, the more you know how to reach your goal, the more fun, interesting and rewarding the process will be.


12.1.1.- Some basics about growth

As we have seen in the post about germination, in the most common (dicotyledon) plants, two primordial leaves called cotyledons are unfolded from inside the seed, becoming the two first photosynthetical factories for the plant. The embryonic stem below them, the hypocotyl, will “shoot” through the cotyledons, producing new leaves that start to hint the mature morphology of the plant leaves. This first spot of growth is the first meristem of the plant, also called the first bud. Buds are the embryonic spots for growth, where fast cellular division produces new plant tissue, differentiated into stem or leaves. In many plants, a change in the photo-period will convert buds into flower buds. People often thinks only of these as buds, since we use the name for the resinous, hopefully big inflorescences in cannabis plants, but the name is not limited to the flowering period.

The apical meristem or terminal bud is the apex of the plant, where the growth flow is pointing at by default. The terminal bud produces the cells that will build a longer main stem, and periodically it produces new leaves.

Nodes are the points in the stem where leaves are developing. Above the spot where the leaves are attached, new meristems are formed. These are known as the lateral buds, and eventually they will produce a new stem shoot and leaves of their own, resulting in branching.



We call internode to the segment between two nodes. Note that the internodes in the terminal bud, in formation process, are very short. The new leaves developing grow above the apex, protecting it as it keeps producing new tissue.

The role of the terminal buds of every branch strongly determines the development of the whole plant structure, particularly in the case of the apical bud of the main stem. That's where the hormones regulating growth, most specially auxin, are initially released. The terminal bud stimulates vertical growth, and at the same time stifles the growth and further branching of lower potential shoots in the lower buds, often called for this reason dormant buds. One of the classic principles of pruning for plant development involves clipping out a terminal bud, in order to cancel its dominance and allow for bigger side growing, turning the plant more “bushy”.

It has been found that the apical bud is dominant not because of its apex position, but because it was there first.



Keeping in mind this basic principle will answer many questions when deciding what to cut. If you also learn about your plant and have proper timing, the possibilities are endless.


12.1.2.- Pruning Method

In general, there's a few guidelines you should follow.

- Any time can be good to prune indoors since we are mostly bypassing the seasonal weather changes, but in regards to the overall growth stage of the plant (or the photo-period you're using) the ideal period to prune is when the plant is more active and it has the best growing and regenerating capabilities. So, if possible, avoid pruning when the plant has more limited resources for some reason, or when it's not yet well established, or when it's using extra energies to recover after any stress such as re-potting. If you prune a plant in bad shape you will give her more stress and waste the potentials of pruning.

- The cuts should be clean, and made slightly above the bud (3-4mm), whether it's fully developed or not – without touching it. If you leave a long piece of stem on top of the new highest bud, that could encourage die-back.

- When cutting above a pair of opposite buds (in a spot where the stem branches symmetrically) and if you want both of them to grow, the cut should be horizontal, and when cutting above a single bud in stems with alternate buds (branches shooting out individually, in alternate directions) the cut should slant upward to just above the bud.



- Whether you use scissors, shears or a razor, make sure your cutting tools are sharp – and sterile. Clean them well in advance with water and soap, and if you intend to root the cuttings you're taking, consider disinfecting them properly with alcohol. Remember you are exposing internal tissues, and those are particularly vulnerable to diseases. We wouldn't like a surgeon to cut us up with a rusty knife either.

- Remember the morphology of your plant and try to help her nature. Plants with a bushy habit will appreciate having their growing tips removed occasionally to encourage side growing, woody plants need to be well directed, and flowering plants will require you to remove the flowers as they fade, to encourage production of new buds and prevent rot.

Also, here's a few more specific tips about pruning for specific reasons.

- Thinning cuts will be useful to clear overcrowded plants that have become too packed and bushy, increasing the chance of plagues, rot and other problems, and blocking the light to the lower branches and foliage. These are usually done by pruning alternate branches from the main stem (leaving the corresponding bud in it) in order to give them space and improve air flow.

- Quick apical prunings are sometimes done by pinching the tip of the stems in the case of soft plants. I don't encourage this since the cut will be more imprecise and irregular, and the stem might be deformed by the pressure of your fingers, but it's a possibility. Actually, interesting things have turned out with pinching – one known example is the so-called FIM pruning in cannabis, where the removal of about three quarters of the terminal bud (instead of leaving it intact) produces some times multiple budding, leading to several new apical buds. The name allegedly comes from the first guy who did it accidentally, pinching more than he intended and mumbling “Fuck, I Missed”.

- Generally there is no reason to keep dying or dead flowers and branches in your plants. These are gateways for molds and diseases to enter, so unless you have a good reason not to, cut them out slightly below the lowest affected spot.

- If two stems are growing close together and rubbing, pick one of them and cut it out to prevent bark damage and die-back.

- Think about the placement and shape of your light and, if possible, try to prune so the shape you induce to the plant will get the most out of it. For instance, if you are growing under fluorescent tubes, promoting several top buds at similar height will use better the radius of the lamps.

- Many established plants have great regeneration properties, and will produce new shoots as long as they are fed and well rooted if they still have buds in the stem. Before throwing a plant away after drought, or after branches and leaves have been sick or damaged, just prune it to her bare bones and hope for buds to sprout again.


Finally, remember it's good to keep in mind the basics of pruning when you want to take cuttings for propagation. You can optimize the shape and structure of your plant as you get new, healthy clones for rooting; we'll talk about that in the next chapter.


12.2.- Training

Some plants, like vines, expect to find an external physical support in order to keep growing. Other plants, due to their growing conditions, might develop too thin or elongated, and become unable to support well their own weight; for instance, the wind blowing outdoors stimulates the grip of the roots and strengthens the stem, so certain trees and bushes isolated from wind will grow more skinny and might end up bending. Certainly, some of this problems can be efficiently patched up with good pruning, giving the plant enough time to thicken, but in some cases training may be necessary.

Other times, training might be another tool for adapting the shape of a plant to the environment, or to give it a specific structure, by forcing it to grow into a certain shape - just think about what experienced bonsai gardeners can achieve. Training can also be a way to build a uniform canopy under the lights, such as in SCROG systems.

The structure, the support or the ties used for training are extremely variable and depend ultimately on what the gardener wants to achieve and the original shape of the plant. One could use stakes, frames, moss poles, weights tied to the stem (when it is getting too tall or straight, and pruning is not desired) or nails in a wall. Plants that might eventually require training include for instance passifloras, ipomoeas and caapi vines.

In the case of plants that just need a grip to stay in vertical position, the most common training structure is a stake. Bamboo canes or wooden sticks make great stakes, and are relatively easy to cut in order to adapt them to the height you need to support. They can be placed as soon as the plant shows signs of bending over, and it's important to make sure that they are firmly stuck in the growing medium. For this reason it's better to bury them in the sides of the pot to avoid damage to the root ball, if possible. Just try to tie the stem gently to them, without squeezing it, and avoid materials that might be abrasive to the plant in both stake and ties.


And for now this is all about growth control. In the next post I'll compile some info about propagation using plant parts, or clones. When gardening indoors, it's one of the most useful and rewarding tricks you have.

Thanks for reading and growing