Females have white pistils(hairs) sticking out like a "V". Males have pollen balls that release clouds of pollen dust. When you know for sure that's it's a male kill it. Plants will flower naturally outside. You can though flower your plants yourself by giving them exactly 12hours of sunlight and 12 hours of total darkness. For the dark period just move it in into your house in complete darkness. But they'll do better if you let them flower naturally. You can only tell the sex of a plant if it's flowering.