by Nebula Haze
Is there a last-minute trick to increase THC right before harvest?
If your cannabis plants are close to harvest, you probably want to make sure you do everything possible to maximize your results. What if I told you there might be a way to increase THC and overall bud quality in marijuana plants, right before harvest time?
Enter the 3-day dark period.
I’ve heard about this tactic multiple times over the years.
Essentially, the idea is to “shock” your plant in the days leading up to harvest in hopes of increasing the potency of your buds. The most common tactic is to place your plants in total darkness for 3 days before harvest. Another tactic is to water your plants with ice water. I’ve even heard a grower say that you should put nails through the main stem to “scare” your plant.
But do these tactics work to increase bud quality, potency, THC, or anything measurable in cannabis plants?
Keep reading to learn more about whether the 3-day dark period works to increase cannabis potency.
Does the 3-day dark period actually work?
I don’t know for sure. I have not seen any grower do an experiment yet besides me. (Check out the bottom of the article for the first set of experiment results!)
From a theoretical standpoint, I personally have difficulty imagining a vast difference in bud quality using last-minute tactics. My reasoning is that THC develops slowly throughout the flowering stage. It takes “work” on the part of the plant to create molecules of THC. Even if stressing the plant increased THC production, how much extra THC could be produced in a few days?
But I’ve grown cannabis long enough to know that sometimes what seems intuitive isn’t correct, which is why experiments are so helpful and powerful.
Check out my other side-by-side cannabis growing experiments.
My experiment: Test a 3-day dark period before harvest
These 2 cannabis plants are close to harvest. They were grown in small grow tents under small LED grow lights.
Square One Genetics special cut plant under an HLG 65 4000k LED grow light (65W) in a 2’x2’x3′ mini tent (check out the full grow journal).
Runtz cannabis plant under a Spider Farmer SF-1000 LED grow light (100W) in a slightly taller 2’x2’x4′ grow tent.
I harvested buds off these two plants from before and after giving them a 3-day dark period.
Let’s see how these buds test against each other in the lab.
- Before 3-day dark period: 18.4% THC average
- Pacific Punch: 19.8% THC
- Runtz: 16.9% THC
- After 3-day dark period: 19.7% THC average
- Pacific Punch: 21.9% THC
- Runtz: 17.6% THC
Wow! This was a spur-of-the-moment test without any controls, so take this with a grain of salt, but it’s pretty stark how much higher the THC tested after the 3-day dark period on both plants. The average is more than 1% higher. I must run more side-by-side experiments to see if this is a fluke. It’s hard for me to believe a dark period could increase the THC this much on a consistent basis.
I wonder if there is some other factor. Perhaps it was natural variation between the buds and it was a matter of luck which ones I picked. It’s also possible that harvesting half the plant caused stress that increased THC in the remaining buds. That would mean it actually had nothing to do with the darkness. Or there may have been some other unknown factor.
A follow-up experiment is definitely coming. This first one was last minute and not well planned. There were no control plants. But the next experiment will involve clones and I’ll harvest plants separately before and after the dark period to reduce the total number of variables. Maybe I’ll think up some other similar tests. Such an exciting time to be a grower!
Closeup of one of the Runtz buds.
Check out more side-by-side cannabis growing experiments.
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