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Will flowering for 11 hours on 13 hours off speed up harvest?

therevverend

Well-known member
Veteran
In Marijuana Botany Robert Connell Clarke cites a study that says twice as much THC is formed under a 12 hour photoperiod vs a 10 hour photoperiod. And that at least 10 hours of light are necessary for adequate THC production.
He also says that shorter photoperiods may cause plants to go into flowering faster. Given 10 hours of light per day a strain may take only 10 days to flower. Whereas if given 16 hour per day it may take 90 days to begin to flower.
Strange and sad how in 2017 a book written in 1979 is still the go to book for botanical information on cannabis, at least that I've found.
The 'shorter day length causing a plant to express equatorial traits' theory sounds like wishful thinking. Effects are subjective, it'd be hard to prove or disprove this. From what I understand a plants traits as far as phenotype are fixed at birth. Of course environment plays a role but it doesn't seem like a hashplant would express itself as a Thai or Columbian from an hour or two less of darkness.
There's a reason most people use 12 on 12 off. It works. I'd only go lower if I was growing a special equatorial strain that needed it. Or if I was in a hurry to force flower. I'm more interested in the other direction, 13-15 hours of light to see if the strain will still flower quickly enough..
 

magnum-opus

New member
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.
yes light decreased at end will ripen plant faster lots data for this from Dr bugbee
 

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