They should'nt grow tall unless they dont recieve enough light.. i'm pretty sure for a good yield you want atleast 4-5 hours of direct sunlight.. if you dont want them growing tall you can pinch the tops.. which will sent energy into branches below making them grow more.. and you can continue this through out thier vegitative growth.. and if you dont want to pinch them.. try buying a hybrid which is just 50%Indica/50%Sativa.. or even an indica..