Long cycling

What would happen if I gave my plants a 27 or 30-hour day instead of 24? I would use a seven-day timer to turn the lights on for 15 to 18 hours and then give the plants a 12-hour dark period. Would this lighting make the plant grow faster or have a larger harvest?
Doctor James,

I think the plants would accept a longer cycle of 27-hour days and continue to flower. The next question is, “Is it worthwhile doing this?”

The idea of long cycling is to increase the percentage of time the plants receive light to increase growth. Under normal flowering conditions plants receive 12 hours of light and 12 hours of darkness each day. If a day were increased from 24 to 27 hours and the plants were lit 15 hours and in darkness 12 hours, they would be lit 55% of the time, an increase of 10%.

Let’s say the plants had a 70-day cycle. For plants cycled to 27-hour days, it would take an additional nine days to complete the cycle. The plants under the normal 12-12 cycle would receive a total of 840 hours of light during flowering and the plants under the 27-hour cycle would receive 1,050 hours. Would the extra nine days, almost 13% more time, induce harvests more than 13% more bountiful? I think they would. Also, the buds would grow larger, resulting in higher quality produce.

I must admit that I have not tried this experiment. If altered cycles intrigue you, try it on only a small portion of your crop. Experiment first, before incorporating the plan into your entire program.

Another way of increasing the percentage of time the plants spend under lights is to find their critical forcing period. Outdoor growers may have noticed that some of their plants begin flowering long before September 22, when the day and night length is each 12 hours. Plants that begin to flower in August or early September are obviously triggered by fewer than 12 hours of darkness. Finding a variety’s critical day length takes either observation of outdoor growth or some experimentation indoors. If a plant were to flower under a regimen of 13 hours of light and 11 hours darkness, it would be lit 54% of the time and under a 14-10 hour regimen it would be photosynthesizing 58% of the time.

There is also the possibility of finding the plant’s critical light period and using longer days. Under the 27-hour regimen, with a critical time factor of 10 hours, the plants would be lit 17 hours of each day, or about 65% of the time.

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