My greenhouse is relatively small, mostly lit by the sun, but is also supplemented by a 1,000-watt HPS lamp. I’m thinking of growing marijuana plants to about 3 feet in height and then forcing them to flower in the springtime. Is it okay to turn back the light to sex the plants? I’m wary of shifting the plants around from flowering stage to vegetative growth because maybe it will mess them up sexually. Is there a way to sex the marijuana plants without putting everything into flowering?
Sexing entire marijuana plants early can set their growth back by a few weeks and can also mess with their sexual expression. One way of determining sex without these disadvantages is by using a proxy. Take a few cuttings from each of the young plants as soon as they develop side branches. Mark each marijuana clone and the plant you cut it off of, and then prepare the cuttings to be cloned. Place the tray of clones under a light regimen of 16 hours of ceaseless darkness and 8 hours of light every day. The clones will reveal their sex in 7 to 10 days and they will all have the same sex as the plant they came from.