Detecting Male or Female cannabis plants is pretty simple to do. Cannabis plants should show first signs of their sex, male or female, within the first 2 weeks of flowering. The pre-flowers grow at branch internodes just behind the leaf spur or stipule about the fourth week of the vegetative growth stage, when the plant is six to eight weeks old. This is when the marijuana plant experiences sexual maturity. Male plants will show “nut sacks” or seed pockets, where female will grow white hairs which are the pistols out from their nodes.