Any research I have done into fertilizer for cacti (specifically Trichocereus pachanoi, aka Peruvian Torch) has suggested any basic all-round fertilizer or cactus fertilizer (but try finding that in canada!! I can hardly find anything but recipes even on the net).

BUT - I have a bucket full of miriacle-gro (24-8-16) crystals - a general purpose fertilizer that I use on my hot pepper plants, herbs and even salvia. Does anyone know if this would be appropriate for Trichocereus pachanoi? Or harmful? or pointless?

I just moved my two cacti indoors for the winter and they are on a 12 hour cycle of fluorescent grow-lights. Should I just let them winter quietly or try and induce more growth by watering and feeding?

i have more questions, but I'll start with these.

Thanks in advance for the input.

JBArk

Cactus ferts are usually very low nitrogen and fairly dilute, but I've never tried high nitrogen so I can't say it wont work from experience. I've heard of people using 20-20-20 diluted to half strength with success. Trichs are really not too picky so I imagine you could try it and at least not kill the plant. Honestly, if you don't change the plants treatment too quickly and dramatically and watch carefully to see if there are any bad consequences to correct for you should be fine experimenting some. I never tried growing triches under lights, but the consensus I read is that a mature trich needs very strong artificial lights to grow normally.

I wouldnt personally ingest anything fertilized with miracle grow..organic worm casting you can get at home depot here in BC anyway, for salvia and other plants..and i think I have seen cacti ferts there..

...and yeah, I learned the hardway to avoid lights with cacti..they only get window light now...they tend to just elongate more than actaully grow otherwise..maybe it was just the lights I had, not exactly sure..

Good advice, thanks! My grow lights seem to be fairly effective - there is still lighter green growth appearing since I put them there 10 days ago... There are 4 high output specialty grow tubes (brand name escapes me...) and they seem to do a pretty good job.

stay tuned for more questions (cuttings etc.)

JBArk

My cactologist - who knows lots about growing all kinds of cacti - recommends up to 50% steer manure in the growing mixture. NOT the fresh from the cow kind, but the aged kind you can buy cheap, sometimes $1 per bag, at Home Depot or the garden center...those bags are often mixed with soil or humus anyway. Then you mix that manure equally with rich composty soil.

Then, without being too mathematical, you can add anywhere from 50-100% by volume of that mixture a blend of sand and pea gravel ... it's for drainage, you want good drainage with cacti ... some add perlite, but that can add to the cost quickly.

Then for a vitamin fix, you might add a little agricultural lime and worm castings...not too much of those are necessary, and you might add them last, to keep them closer to where the plant will begin rooting.

(Gardening tip for Nexians: leftover pulp from those 3X3 pulls of caapi, chaliponga, jurema, chacruna is rumored to make INCREDIBLE compost and humus.... and not just for cacti...add it to tomatoes, peppers, letttuce, fruit trees ...)

get the 10-10-10 kind, they have it at home depot, a yellow bottle. Works all year around. don't water them in wintertime, they won't grow, only rot!

Ouro - testing it now. thanks!!

fractal enchantment: I understand your concerns, but it's off season here so its difficult to find any natural fertilizers, and I happen to have a tub of this stuff. Next spring i am going to look around for some natural ferts and use the MG only for non-comestibles. By the time my cacti get big enough to ingest, there will surely be not MG traces left anyway...

Pau: the cacti are already planted in a commercial cactus soil and have been transplanted into larger pots. What I am looking to do is feed them occasionally because I believe by now they have surely exhausted any nutrients in the original soil.

oetzi13: Its winter, but they are inside at 20C under grow lights, so i am not worried about rot. I was just wondering if they needed a seasonal drought to grow more profusely in the spring.

Thanks everyone for the tips, feel free to add anything else! I am a budding gardener and know very little about cacti.

JBArk

Just on the OP - It is my understanding that you should in no way use a fertiliser with an NPK of 20:20:20 on cacti! They are generally too slow growing and this amount of feed is way too much. These are hardy plants designed to thrive in soils with few nutrients. You are very unlikely to have a cacti die from underfeeding or lack of watering, but overfeeding or excess watering can cause all sorts of problems.

You might get away with it with san pedro, if it was very, very slowly introduced, but if anyone reading is thinking of using that on peyote - it would probably burst the cacti, and may even kill it.

You should only feed cacti when they are actively growing, ie spring & early summer. I have a specialist cacti feed, and its NPK is 1:1:3. I use it sparingly.

I find watering in Wintertime has no benefit at all. Remember it's a cactus, it likes it dry. Even though this specie likes water in Summer; in winter it likes to rest, - especially if you have them in soil. It's easy to overdo it, trust me, I have killed many by being too concerned. Just leave them alone

To effectively grow a certain plant one should ask the experts in the field. I know there is some good british cactus forums out there.
Perhaps you want to check those.

But to share my thoughts on cactus fertilizers... : )
Since they grow relatively slow compared to other plants, and as a result need on little amounts of nutrients, one is considering to use aquariumwater. Within a aquarium there can be a very simple and basic (not tooo delicate) balance between some simple waterplants for providing oxygen, some small fish for providing shit, and some bacteria to convert the fishshit (containing ammonia) into nitrates and other nutrients. The water from such an carefully prepared aquarium will contain lots of different nutrient(complexes), perhaps even vitamines, hormones etc. NPK would be low i guess, something like 1-0.5-0.5 ?

I wonder how well cacti would thrive on such aquariumwater... Calcium and magnesium could be a problem because of biogenic decalcification in the aquarium (organisms like algi taking these minerals out of the water) but probably the use of some basalt and crushed seashells in the soil medium can help out there.

Also i see possibilities for rooting cacti cuttings on heavily aerated aquaria mini-ecosystem. Could help speed up peyote grafting experiments i see elsewhere on the forums. The artificial light can be used to: power the photosynthesis in the cactus and simultaneously power a nitrogen cycle in the fishtank underneath.

I have seen other threads like this. Might be fun to read them all and come to an experiment. I have been thinking about setting up some simple experiments using some fish (Poecilia reticulata) and waterplants (Elodea canadensis). Im interested to see how the water changes. I would be using simple aquarium testkit to get some rough idea. If the aquarium water has certain pH due to decalcification, it could be perfect for let's say growing or rooting cannabis also... as an alternative to using rainwater or (hard) tapwater. But i wont attempt anywhere soon, atm i have got way too many projects running already...