Hey

To tell the sex you must wait until it buds. To bud a plant you just have to switch the photoperiod from 18h light/6h night to 12hlight/12h night. Then after 3 weeks (minimum) you should be able to see some litle "balls" developing on the nods and on the head of the plant. How to tell from a female and a male. ITs quite simple : females haves litle balls with 2 strings coming out of it (about 5mm long) it is called pistils. The male on the other hand have just litle balls with nothing else. When the male flower opens its like an umbrella.

I hope this will help see ya

P.S: this is a pic of my...hermy...(hermaphrodite?) and you can se the female flowers on the top and the male flowers on the base....if you see a plant like that just trash it...its nothing more than trash.