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[Mark_Antony]

Hey fellas im interested in possibly growing my Trichocereus cacti under lights but im not sure what the best choice would be or if its even possible. I have found mixed information online and i cant seem to get a straight answer on what light would be the best. Im currently growing my 1 year old seedlings under lights but i know they will need something more powerful when they begin to grow bigger, So any information you guys can provide on growing them under lights would be helpful.

[Auxin]

The stronger and more 'natural' the light, the better. But make any large changes slowly.
Once they have grown under the sun for a time its best to just make them go dormant all winter unless you dont mind etiolation.
If your starting up seedlings or plumping seedlings up on pereskiopsis the 'daylight' spectrum CFLs work well for indoor lighting and are affordable.
Beyond that, anything that could grow cannabis indoors could grow cacti indoors, with notable etiolation.
If your cacti will never be grown under the sun or if you dont care about a sinusoidal shape of the stems just give them as much 'daylight' spectrum light as you can and dont go too nuts with fertilizer, as softer growth may be more susceptible to rot.

[Mark_Antony]

So by daylight spectrum do you mean in the around 6400 kelvin range?

[Auxin]

Yes, 5000-6500+
They should say 'Daylight' on the box.
And please, dont use one as your porch light, those things are blinding at night

[geezer]

give some thought to how tall your columns are and how-to light with what kind of fixture

light gets weaker as it gets further from the source. it takes a badass bulb with a strong power source to light well from 6 inches down to six feet down. I learned this in my hydro vegetable garden. you can burn stuff too near the bulb and get poor performance from things too far from the bulb

if you were trying to use a small cfl bulb to light a two foot tall column from the top you'd not get good results. those cfl's meant for growing lettuce in a hydro pot (for example) are only intended and capable of lighting for a few inches

it would be great to light evenly from top to bottom. so maybe a 2 foot long flourescent fixture fitted with daylight bulbs standing on it's (narrow) edge would light tall columns best. I'd guess a four bulb fixture could light 6 or 8 columns of 3 feet tall or less

and you'd have to give some thought to either rotating the pots so the columns get even light, or have a second fixture on the other side of the columns but I'll confess that's getting a bit anal

maybe a qualified horticulturalist has an opinion about the right or wrong of lighting from the side instead of the top. they get lit mainly from the top out there in nature so maybe there's a consequence to side lighting???

[geezer]

if there's a hydroponics store near you they'll be your best friend on figuring this stuff out

and another thing learned from the hydro vegetable days - running lights is expensive. try to get the best use out of every fixture. If you could grow some lettuce in the voids between round pots you'd be helping amortize the electric bill.

[geezer]

not perfectly translatable to cactus growing but this video has useful info about types of lights and a brand name or two



hopefully it helps

[coAsTal]

I have a couple sets of LED's in the 4-foot long T-5 (flouro) format that were very inexpensive (~$50 for a set of 8 )
That's about 25% of what 8x "real" T5's go for, and these are only drawing 20W of power each. They're 6500K light temp @2200lm each-- and cool burning-- and silent.

I am using them for my seedling rack, but they will also be more than sufficient to grow small grafts to several inches tall on pereskiopsis. (or whatever)

I've always read that it's a big challenge to grow adult trichs indoors, and is generally not recommended because of the likelihood of etiolation and generally poor results unless you were to drop hardcore wattage/$ on them.
That's not really worth the trouble and expense for a couple of columns when you can just winterize them until spring then get them in the sun.

...but I don't think I've seen anyone wrap them in vertical flouros before, and I have enough of these that I might try that for kicks one day-- kind of a cylinder of tubes in a ring around one of my cuttings... 

[CalyxCrystals]

Okay this is a multipart answer...

TL;DR-Your seedling will be fine under T5s or similar until the reach 8"+(maybe more). Don't waste the time or energy to grow them indoors after that. Let them go dormant in a heated greenhouse or any room in your home that stays between 35F-60F.

As for your seedlings:
Depending on many factors (light cycle, fertilizer, watering frequency, etc) you could maybe get away with just T5 shop lights for a couple years. I havent used them much, and not for anything bigger than 6" tall, but i assume you could probably get to 1' or so before you started to notice any decline in grow. Due to lumen/lux/(whatever unit you want to use to measure light intesity) drop over distance being exponential (see Inverse Square Law of light) the amount of green skin exposed to enough lumens for optimal growth, will drop drastically as the cacti increases in height. Thus etoliation. You could add supplemental side light, or even implement a vertical style grow setup, but the energy cost will soon become unreasonable.

As for Adult cacti:
I wouldn't even attempt to grow anything over 1.5'-2' inside. Even with HID lighting 18" can be a drastic drop in light intensity. Your cacti will etoliate without careful planning, lots of supplemental light, and a massive increase to your electric bill.

I currently have about 25 cacti ranging from seedlings to ~16" rooted cuttings under a 600w MH. This is just to fight etoliation as best i can in winter as i have no room in my house that stays cool enough to make them go dormant. It might work for this winter, but next winter I won't even bother trying. Greenhouse will have to be built.

In the wild some of these trichs will reach 20ft or more, but the sun does not have a noticeable lumen drop over 20ft. Thus all the green skin can be used for photosynthesis and produce fat and tall columns. Trying to replicate this indoors is futile. It could be done, but i dont wanna be the one paying for that electric bill.