I’d like to force a marijuana crop to flower. What do you suggest I do for best results? Should I go from 18 hours of light to 12 hours of light immediately or over a gradual length of time?
As a short-day plant, marijuana flowers when it receives around 10 to 12 hours of continuous darkness for each 24-hour period. As soon as the plants start to produce flowers, change the concentration of the fertilizer to a formula high in phosphorus (P).
When the marijuana plants experience 8 to 12 daily hours of uninterrupted darkness, they will switch from vegetative to reproductive growth in which they will begin to flower. You don’t have to make the switch gradually. The marijuana plants will respond favorably to any changes in the light regimen.
During the summer, outdoor marijuana plants in Florida will flower earlier than those in Vancouver because of the amount of darkness it receives. They will start flowering when a critical dark period is achieved. Many varieties require between 8 and 12 hours of continuous daily darkness to start flowering. To figure out the critical dark period, observe outdoor marijuana plants and notice when they start to flower. Figure out the amount of darkness the plants experience when you start seeing flowers. Then, count back to the darkness period of the prior fortnight. For indoor marijuana plants, start the period of darkness at about 9 hours and then increase the amount of darkness by 15 minutes for each week. The critical period should be around 15 to 30 minutes shorter than the dark period length when you notice the initial flowers.
Let’s say a plant’s critical dark period is exactly 10 hours. It should flower adequately under 14 hours of light. This is essentially two extra hours than normally recommended. Even so, the two extra hours will produce about a 16% increase in overall light that gets to the marijuana plant. More light directly correlates to increased growth. If the period of darkness is shorter, the flowering stage might last longer. You can lengthen the dark period to 12 or 14 hours if you want the buds to ripen faster.
Tony