If your box is only 3 feet tall, you need to flower sexually mature clones immediately. (Clones that were taken from a sexually mature female.) That's if you want to try a sea of green.

However, with only 3 feet, I dunno if that'll work very well. My clones, that I flowered at 3" or 4" in height, are now more than 31" tall, not counting the pot, after 29 days of flowering. Counting the pot, they are 3 feet tall. If that happens to you, you'd have 0" for light and space between the light and the plants, which wouldn't work.

So, I recommend Screen of Green. Put your light as high up as you can get it. Create a screen out of whatever, and put that about 8" above the soil line. Then grow your plants until the screen is a bit more than half filled with bud sites. Then flower, and if anything gets too close to the light, tie it off to the side. Once you start flowering, wait until the screen's full before letting them grow vertically, and no matter what, wait at least a week or 10 days because height is going to be an issue. I have a feeling it's gonna be pretty dang tight in there. I'd use two or three plants in smallish pots (small = not tall), but don't use seedlings, just clones of a female, because if they prove to be male, disentangling them from the screen could suck. I'd say just try ONE plant unless you're using seedlings, then I'd go with three, to better the odds of females.

If you *have* to use seedlings, and that 3-foot height is all you can use, then make small screens, instead of just one big screen, and use wire-snipped coathangers and duct tape or whatever to attach a smaller screen to each individual pot. That way, if you get a male you can just pull that pot/plant/screen combo out as a unit.

Hope some of that was helpful.