I have about 30 Bridgessii, Pachanoi and Peruvianus seedlings here at nearly 4 months old and winter is fast approaching. I am thinking I may just keep them under lights for the winter rather than let them go into dormancy.

I’ve had a brief look at lighting for cacti and looking about at most shops that sell lighting set ups I can see seem more aimed at leafy plants that require a lot of power to penetrate through leaves.

What kind of wattage/light spectrum/bulb types should I look for to look after my seedlings through the winter? I don’t need to cover a very large area as my seedlings are in 6 small pots so the space they take up currently is probably only 40cm/30cm.

I would get something small, like 75w even, and have it above a layer of cotton that is set up above the seedlings so that it filters the light somewhat. The seedlings might find direct light to burn them. If not, then you don't need the layer/roof of cotton (or some other kind of thin sheet.)

2-basic 24"x20W fluoro tubes worked well for me

they stay cool, so the lights can be a few inches from the cacti, or as close as an inch

Do you mean just general purpose home lighting-type bulbs?

I think for my current space situation I want to get something a bit smaller, possibly either one or two CFL bulbs or an LED setup. I was thinking as they will probably have to sit in the corner of my room I would probably construct a box for them so I don’t get disturbed by light from them, and could also probably help make the most of the light by bouncing it off the walls.

Will they be happy with these? Should I get a blue bulb setup, mixed red/blue, standard home use bulb, daylight bulb set up?

A buddy gave me an aero garden. I disconnected the water pump and put a few 1yr seedlings and an lw up there to see how it goes.

I will keep you posted.

I've kept my cacti indoors under a 400 watt, full spectrum CMH bulb and they grew all through the winter at a rate at least equal to that of spring/summer.

I know this doesn't really make sense in your situation, just thought I'd share.

I'd go for CFL over LED's...the best LED's I've seen are incredibly expensive to get decent amounts of light and there's no sense in spending money on lights that don't actually put out usable light.

I will probably look into CFL then, I would rather keep the heat output and power usage down if I can. I see quite a few very reasonably priced CFL bulbs that will fit into a regular bayonet (and I suppose screw must be about) fitting on Amazon.

I've got about 30 seedlings under a 400 watt metal halide , seems to be going pretty good so far.

full grown cacti and grafts do very well under a 400mh, and even better under a 600hps
fairly high electrical usage for cati though imo

here is a old pic for reference

For good energy efficiency you could consider a LED grow system. These work well and are (I think) 4 times more efficient than CFLs. They use ~10% the electricity of metal halide lamps. Here's one source: Sunshine Systems

What % of the light emitted is usable by the plants? The vast majority of LED systems are pathetic, imo. Look around at any growing forum and the general consensus is that LED's are not quite there yet. If you look at the link I provided above, you will see that in order to get good results from LEDs, you have to shell out a pretty penny.

T5 fluoresents will do well and are fairly cost efficient
forget about regular T8

I will look into T5 bulbs, they look very promising. I hadn’t really looked into fluorescent too far yet but they do seem to make a lot of sense in comparison to CFL.

Snozz, I think it depends on what you are trying to do. The LEDs are very directional because each emitter has a lens on it to direct the light down to the plant. Metal Halide or fluorescents emit light in all directions (and that is why they typically have a reflector to try and concentrate the light a bit.

You can purchase a fairly cheap LED array that will illuminate 1.5 square feet for about $55 (cheap LED). (so they say). A series of fluorescents will illuminate a larger area.

The nice thing about LEDs is their efficiency. About 33% of the electricity goes into making light. Other types of lamps are much less efficient (fluorescents and HID lamps are less than 10% if my memory is OK). I suppose for equal areas of illumination, the LEDs are more expensive but you have to pay more to run them. A 75W lamp costs about $1.00 per day to run 12 for hours. An equivalent output LED lamp uses ~14 watts and would cost about $0.21 per day to run.

The spectrum of the LED arrays is typically composed of red and blue. Plants like this spectrum. With fluorescents, much of the energy is green which does not promote growth since plants reflect green light.

LEDs also last a long time so you don't need to replace bulbs. The initial cost may be higher but the payback in energy costs may be worth it in the end. I have an LED array and it works well for growing seedlings in the spring. I have not tried to grow cactus with it.

Right and whats the degree of the lenses they're using? This has a HUGE effect on the intensity of the light emitted for LEDs.

What's the actual wavelengths they are putting out? Not "red" or "blue" but the actual nm?

These are the specs that actually matter and range drastically from cheap LEDs to top of the line ones.

I put in a ton of research when looking into lighting several years ago and have generally kept up with whats going on, imo.

There's no sense "saving money" on electricity if the electricity being used does not go towards putting out usable light of a decent quantity. Just because a light turns on and looks bright, doesn't mean it's good for plants...lumens have nothing to do with how a plant processes light.

Additionally, you can't make generalizations about fluorescents like "much of the energy is green" because it depends on the color temperature (k) of any specific light, which can vary pretty much across the entire spectrum (just look around the lighting section in a hardware store and you'll see this to be the case).

So while your argument for LEDs looks good in a generalized sense...it fails in actuality, which is why good (read: effective) LEDs are still ridiculously expensive for the actual amount of usable light they emit (if you haven't looked at the link I provided earlier, please do, those are literally the best LEDs I have seen discussed on any growing forum).

I would aim for 30 watts per square foot minimum with HID lighting.

I would never let San Pedro go dormant if I could help it, it does not do this in nature. Actually in winter in the Andes these plants get lots of cold and rain, the winter is the Andean wet season.

LED lighting is a very poor choice, the spectrum is far too narrow and the lighting intensity is far too weak to result in any ideal growth. Also in terms of effiency and spectrum CMH metal halide HID bulbs are both top of the line and the best tech we have at present, they can provide 100 lumens per watt! Some experimental LED lights are a bit more efficient but have far too narrow a spectrum to result in decent growth.


Not one side by side comparison of LED to HID lighting has shown LED to be superior in terms of growth.
Please prove me wrong on this.
I dare you.

The hydro grow LED comparisons hosted at icmag came pretty close...but

Once people reported typical yields of 1gpw it destroyed the comparisons they were giving the lights, so the LED they had presented as equivalent to 400watts HID was dropped to 2 something, the 600watt equivalent was dropped to 400...yadda yadda...ultimately the lights became even more expensive per comparable HID fixture. Now that they adjusted those comparable ratings, they're close but take a somewhat ridiculous chomp outta your wallet.

Cool, thanks for the information. I believe that one day LED tech will render HID obsolete, we just need LED lights with a CRI of 100 and a Kelvin temp of 5000-6000 and a lumens per watt ratio of better than 150:1.

If the cactus is long enough the fluorescents can be put vertically for maximum coverage. Perhaps a cilinder of reflective material around the cactus and tube, so one wouldnt need an 'official' reflector for the tube. It would be warm, ~30C i guess, in the cilinder that would act as a chimney. Put something on a string just above the cilinder and it will move gracefully Carefully placed holes in the reflective material could be used to cool the cilinder, and somehwat light the surroundings too (fishbowl with guppy fish and waterpest plants for biogenic decalcification and subtle fertilisation of the water?)

Otherwise there are punctured metal sheets available at your local DIY shop, that can be bend into a cilinder. If the material isnt reflective enough then the inside of the cilinder can be made white for maximum reflection. the outside can have a pretty color for all that matters.

What im trying to say, an artificial growing setup doesnt always have to be ugly and secret.
A setup could be aesthetically pleasing as well, for all to see and admire. hail hail.
and non of the energy has to be wasted.

As I’ve been spending far too much on growing experiments over the past months the cacti fell to the wayside and then winter appeared!

I’ve ended up with a 1ft³ box in my record shelving for my cacti to live in over the winter and a single 30W/6500K CFL. Maybe I might supplement it if they don’t seem happy in that situation. I’ll drop in a pic when I have the camera out next.

One question on timing for over winter growth – is 12/12 an alright regiment for them?