tried & true if you want to sex b/4 flippin, let plants get to 10th node & start looking @ 8th node & you will be able to tell. apprx. 6th week of veg. also use a jewlers loupe to assist in sexing(30x for $15 online). last grow i wait in flower w/o loupe and didnt get all males in time & now have a few seeds here & there, but this time goin all sensi.