I agree with Zandor.

you can do either, but i supose sexing a seedling is better, cos then your not wasting time growing a big plant and then having to kill it.

You CAN wait, but 3 foot sounds a tad tall. They will finish at atleast double that size, so you gotta be sure theres enough room in the grow room.
LIP Reviewed by LIP on . SEX Please offer your good advices - A friend of mine and I have a disagreement about sexing seedlings when placing them into the 12/12 cycle. I say that you should sex ASAP when the plant is only 4-6 inches tall with just a couple of sets of opposing leaves. He says that you should wait until the plant is older, fully mature, with many branches and ready to flower permanently; minimum 2-3 feet tall. What do you think ladies & gents? Rating: 5