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Cannabis circadian rythms

Knowing that cannabis is a night-length dependent crop (meaning it needs a photo period with a night cycle equal to or greater to 12 hours) to induce flowering, what are your general thoughts on how to manipulate this to increase crop growth. In an earlier post, I talked about how increasing the night period from 12 hours to 14 hours the last half of the flowering cycle. However, what I am pondering now is what would happen if we gave the crop 14 hours of light, followed by 12 hours of night? The plant needs to have only a period of un-interupted darkness for at least 12 hours. Nothing is being said that the plant only needs 12 hours of day. As long as the night period is un-interupted, and 12 hours in length, what would happen if we gave the crop 14, 16, 18, 20 hours of day period followed by a 12 hour night period? Would the increased period of light result in increase in carbohydrate production? Faster vegetative growth? Quicker maturation time?

I know that commercial potted flower production plays around with a similar theory and has great results. Things like mums and rudbekia respond well to this type of photoperiod manipulation. Interested in knowing your thoughts on this?


This seemed it might be relevant to this discussion.

"Phytochrome is a pigment that is found within the leaves of all plants, as well as cannabis. The role of this pigment is to detect light to then allow the plant to grow accordingly based on the season or time to induce flower production. When light hits the surface of a leaf, there will be two types of light sensors at work: one which has the job of detecting blue light and one for detecting red light.

The one designed to sense red light is the phytochrome system."


correct, and when phytochrome receives 100 umols of light, then its activated. Anything below that and it will still stay within its night cycle. Whats funny is everyone always wants their night cycle to be pitch black…but in nature, on a full moon, sometime there is up to 70 umols of light and it doesnt disrupt the plants cycle.


There was actually an interesting paper by Bruce Bugbee about growing on the moon (I started a topic about it). Because the moon has roughly 14 day-long day periods and 14 day-long night periods (one new moon every month), NASA wanted to explore the possibility of using fiber optics and what growing with long dark periods would do to plants.

The interesting takeaway from his paper was this:

[quote]“Tomatoes went into storage just as the plants were flowering and a PPF of 10 was
tremendously beneficial. Slightly reducing air temperature, along with a PPF of 10,
increased yield by a surprising 80% above the control plants. The tomato plants effectively
set fruit during the cold, dark period, and these fruits rapidly grew after full light was

Crop Production on the Lunar Surface Using Solar Fiber Optics- M.pdf (758.4 KB)

Having an unusually long dark period caused the tomatoes to catapult their fruiting when light was restored. Pretty neat, huh?