5' X 5' I'm vegging 12 ladies in a 12 pot ebb & flow under a 1000w MH. I was told by the gays at the hydro store that I should veg 12, then only flower the 8 healthiest in this space. The strains are xj-13 & Hindu $kunk. so whats the real deal?
I think it depends on how long you veg for. If you go for 6 weeks, until preflowers show and the plants are around 24 inches, then you should only flower 8 plants (about 3sqft per plant). If you veg for more like 2 to 4 weeks and the plants are only 14 inches tall then you can keep them all. Either way you're going to get about the same sized harvest. Keeping all the plants will make it hard to move around and increase the cost of nutrients though so take that into consideration.
I tink you can get all 12 in there. At 25 sq ft you'll have a bit over 2 sq ft per plant, that should be plenty including a little maneuvering room. You probably want to rotate plants from out in the corners to under the light. EDIT: unless you're going with huge pots 10+ gallons.