if i was you, id top the plant in a couple places before i started flowerin bro. i mean, they already look bushy as shit so im not sure if u already did or not, but if you top them, not only will you have more than one main cola, but you will also be giving the plants time to strengthen up some more, while keeping the height down at the same time. So you could top each plant like twice, and give each plant some breathing room for a little bit, and then whenever the branches grow back, put a screen over top of the canopy right before flowering. Do a scrog with what you got goin on man - everything is so crowded anyways, your only gonna have the top half of the plants produce any typa decent buds, so why not maximize its potential?? top each plant 2-3 times each, and throw a screen like 5-6 inches above the topped plants. when the branches grow back they should be just startin to touch the screen, then hit them bitches hard with the hps. Once they start flowering, then youll see the real magic happen man. since you got some fem seeds, you wont have to worry about pickinout males n shit like that, so ScrOG is the best way to go for a crowded situation like yours man. BREAK OUT THE CHICKEN WIRE!!!