Can you increase THC by giving marijuana plants continuous darkness before harvest?

What’s your opinion on giving the marijuana plants 24 to 48 continuous hours of darkness just before harvesting? Some people have suggested that this increases the THC on the plants.

n the 70’s, a University of Mississippi doctor named Carleton Turner showed that THC amounts seemed to differ based on when the marijuana plants were harvested. The potency tended to be increased just prior to dawn. In 2000, Dr. Paul Mahlberg at Indiana University discovered that THC was produced in an extracellular fashion in the center of the glandular membrane (which permitted for daily recycling).

Thus, your theory certainly requires some research, but it might hold true. Turner’s research showed that long dark periods produced the best environment for THC production.


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I have done this and in my personal opinion I think it does seem to make the plant more “resiny”. So I always do it, it doesn’t seem to hurt anything so why not! :lol:

Thanks for this tip about best THC levels - I would assume this is also the case with other Cannabidiols like CBD.

I did this for one harvest - and I think it did make the plant more resiny - but then forgot about it…

… and now that I’m doing screen of green in a flower room with perpetual harvest of a few plants every couple weeks, I cannot move the plants and I cannot change the light timing - I’ll just have to harvest just as the lights are coming on…

Joey from the JuicedCannabis Channel on YouTube.

I can assure you that it does increase the THC levels. You can think of it this way. The resin is what the plant produces to trap the pollen from the male plant. This is a survival response genetically programed into the plant.
The plant does not produce the resin if the negative phase because the 18/6 light cycle makes it think it is spring or summer time.
The light cycle change to 12/12 makes the plant think it is fall, and time to breed to assure the continuation of the species. The buds form and produce the resin required to trap the pollen and form seeds. If the plant does not get pollenated it starts to produce more and more resin. This is why you will see the resin increase the most toward the end of the flowering phase. It is like the plant is in panic mode trying to catch ant pollen it can. Now if you turn the lights off totally for 3 days before harvesting, the plant puts all possible energy into this last ditch effort to be pollenated.
Now I also no people that have tried increasing the periods of darkness from 12 to 14 to 16 then 18 hours to push resin production. The plants only goal is to reproduce, and senses the increased darkness as winter and the end of its life.
The down side of this process is that you risk the plant becoming a hermaphrodite, and pollenating itself. That is why I only black them out for 3 days. It is not enough time for the plant to herm out.
I also cant give you a number that this increases the THC level to, but it does increase

Sorry this response got so long



Is more than 3 days of darkness to much right before harvesting