this is a tough question to realy answer..are you growing from seed? or is this a clone? I take tops of the spotted female and thats the clone, takes from 4-7 weeks to show sex..by this time plants 18 inches roughly. if I am working with a cloned female...then anytime after its roots established..useually 3 weeks after cloneing..I dont think its a hight thing..as I have cloned at diffrent sizes..just dont take more the 1/3 of plant, you will be fine. hope I helped a bit