He said it was a test run to validate the process - they were 12/12 from seed in 4" rockwool cubes packed together in an ebb and flow setup. He said they got 18 inches or so with one big cola. Been thinking of trying something similar but the seed cost would kill me. I might look into making some feminized seeds of my own from my Plushberry clones I've been growing this year.
Depends on a lot of things. The size of your canopy, what wattage you're running the board, age of your plants, etc. Good rule of thumb seems to be to start high, say 24", at less than full power, and adjust as needed. At least that's what I've picked up from reading the threads here; but I'm admittedly a noob, so a more knowledgeable LED grower may step in and correct me.
Just be aware that plants don't always react well to a change of lights mid stream. It's better to start higher and with less power than you think, and step up from there if they tolerate it well.
