Determining the gender of marijuana plants can help with separating male from female plants. However, this is only possible to do when the cannabis has started with their flowering cycle.
Cannabis plants start to flower when they receive 12 hours of light and 12 hours of uninterrupted darkness in 24 hours. When this begins, a plant enters a pre-flowering stage where they increase in size because the branch structure prepares to carry and support the weight of the flowers.
Telling the gender before flowering
During the pre-flowering phase, which lasts around ten days, it is not possible to identify the sex. The first flowers should appear within the first two weeks.
The use of feminized seeds or automatic seeds eliminates this process because they are made to produce plants that flower only as females.
Inducing flowering for the sexing of marijuana plants
The grower decides when to alter the photo period and induce the flowering when growing the plant inside. You do this just by adjusting the timers on the lights.
In the outdoor conditions, the grower will have to wait until natural daylight hours decrease to 12 per day. When this happens occurs in the region of course. In Northern Europe, this period starts in the middle of July.
You can also induce flowering outside by allowing your plants 12 hours of daylight every day, after which you either cover them or take them inside. Just make sure to do this every day, because if darkness periods are interrupted by the sudden light, it affects the plants severely and sets them back to a vegetative state.