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I haven’t seen any new research on altering the plants’ day from a 24-hour cycle to an 18-hour cycle, so I don’t know whether they could adjust to it or if they would experience problems because of it. We know that when plants are under constant light they stay healthy and grow well. They don’t seem to exhibit any circadian rhythm, so there is a possibility they could make the adjustment and they may very well reach maturity in a much shorter time.
Plants need 12 hours of uninterrupted darkness to trigger flowering. Since an 18-hour day is only 3/4 of a full day, there might be a 25% time saving, but the part that has been cut out is six hours of light.
Plants use light to fuel photosynthesis. Through a series of chemical reactions, plants photosynthesize using light energy to convert carbon dioxide, an inert gas plants mine from air, and water into sugars. Some of the sugars are combined with nitrogen to form amino acids and other tissue building blocks. Some of the sugars are used to fuel the plant’s metabolic processes. As far as green plants are concerned, you could say that light equals growth.
During flowering, lights are typically on for 12 hours of a 24-hour day, so plants receive light 50% of the time. If the lights are kept on for only six hours of an 18-hour day, the plants are receiving light during roughly 33% of the flowering period cycle. A 17% reduction in light means the growth rate will be considerably slower. Because they are still getting the same amount of darkness as on a normal 24-hour cycle, the plants will ripen in 3/4 of the time. But if the plants adjust to the new regimen, their yield would be considerably smaller than normal.
To speed up flowering you could place the plants on a 10 on/14 off schedule during the last few weeks of flowering. They would receive light 41% of the time. Another schedule that you might try would be 10 on/12 off?a 22-hour day. Under this scheme the plants would receive light about 45% of the time so their yield would be only be slightly reduced.
It might be possible to increase the yield by manipulating the light regimen. If the plants were placed under a 14 on/12 off or a 16 on/12 off lighting program, they would receive light 54% and 57% of the time, respectively, so their growing time each day would increase 8% and 14% respectively, but the daily cycle would also increase. Although they would take longer to ripen, they would have both a higher gross yield and a higher yield in relation to the time spent in flowering.
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