height to start flowering

Im new to growing and want a bit of an idea im using a normal aerogarden and was wondering if the aerogarden would restrict the height of my plant in terms of root space. so i was wondering what height should i veg to shes been going 4weeks and its red cherry. Ive got a 1.8m high tent with a 400w hps under a wing.

It varies but the usual height I veg to is about a foot to a foot and a half heres a pic of what I would consider fully vegged plants they are about 14 inches from soil level and took about 50 days to get there. You could veg for a little shorter time but most would agree to give it full term for best yield.

thanks mate ill switch over to 12/12 in a few days then mines at 12.5inches atm