I sexed mine about 3 weeks after they sprouted. It actually was an accident. I was doing 10 hours natural sunlight, 8 hours 400w MH and 6 hours darkness. All 4 plants (2 master kush and 2 early misty) showed sex. 3 were fems. The lone male showed its balls and it was only about 4"! I have them under 18 hours MH now to revegg.