Darkness Before Harvest: Is It A Myth Or True?

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If you are growing your own weed, and it is coming time to harvest, you want to do everything in your power to ensure that your weed is as potent as possible.

One theory here, to make your weed as strong as possible, is to keep it in the dark for a few days prior to harvest but is this whole darkness before harvest theory actually true? or just a myth?

Although there is limited scientific research on this front, the evidence does point to the fact that a darkness period right before the harvest can in fact make your weed stronger, or in other words, greatly increase the THC content.

Darkness Before Harvest Myth

Let’s take a closer look at why this might be the case.


Darkness Before Harvest Theories: Does It Actually Work?

Keep in mind that there isn’t too much scientific research that has been performed on this front, although by all indications, it does appear that a period of darkness before harvest, whether 24 hours darkness before harvest, 48 hours of darkness before harvest, or even three days of darkness before harvest, that it does increase THC levels in your bud.

Now, in some cases, the THC might only rise by a fraction of a percent, whereas in other cases it may increase by several percentage points.

Now, as far as comparing a 24 hour, 48 hour, and 72 hour darkness period goes, it does appear that the longer this darkness period is, the greater the effect will be. Most people recommend doing a three day darkness period right before the harvest, as this will produce the best result.

All of that being said, you’re now probably wondering how a darkness period before the harvest helps to increase THC levels.

Although there is no concrete proof, either way, there are a few leading theories as to why this darkness period can help to increase THC levels in your weed, so let’s take a quick look.

The Stress Factor

One theory here is that increased levels of stress, even small shocks to the cannabis plant, can temporarily increase THC production.

Although exactly how increased stress levels cause higher levels of resin to be produced in buds is not known for sure, it is still a leading theory nonetheless.

An Evolutionary Mechanism

One of the leading theories as to why a darkness period before harvest increases the THC level in weed is due to a simple evolutionary mechanism.

The logic behind it is that weed plants start to flower in the summer, later in the summer. When the days start to get shorter, and weed plants get less light, it is a sign to them that the season is coming to an end, and if they want to produce seeds and reproduce before winter comes, they must get busy.

The later on in the season it gets, the more flowers the female weed plant produces in the hopes of being pollinated. Darkness is a sign that winter is coming, which causes female weed plants to go into overdrive.

Light-Based THC Fluctuations

Another possible explanation here is that THC levels in your weed are the highest after a multi-day darkness period due to natural fluctuations in THC in plants.

The cannabinoids contained in weed help to protect the whole plant from damage caused by UV rays. The more sunlight there is, the more cannabinoids will degrade over the course of the day as they battle against the UV rays.

Then, during the nighttime, the cannabis plant produces and stores as many cannabinoids as possible to ready itself for yet another day of warding off the sun.

Therefore, if you leave your plant in the dark for a few days before harvest, it should increase THC levels.

Do Buds Get Bigger In The Dark?

Although there is some evidence, mostly firsthand anecdotal evidence from growers themselves, that a dark period can increase THC levels significantly, making the buds bigger is not something that happens.

Just think about the fact that it can take up to three months for your buds to reach full size. So, why would there be such a significant increase in size from just a few days of darkness?

After all, during the flowering stage, your plant is already getting 12 hours of darkness each day. So, if buds grow so much during the night, then why aren’t yours significantly bigger each and every single morning?

The simple reality is that although a dark period before harvest may increase THC levels in weed, it’s not going to make a noticeable difference in terms of size.

Does Darkness Increase Trichome Production?

The terpenes contained in your weed are the substances that give it its aroma and flavor, so the more terpenes your weed has, the tastier it will be.

Just like with THC increasing during that darkness period, so do the terpenes, theoretically. It is once again important to note that there

haven’t been any scientific studies done on this front, but thanks to some common sense, it does seem that this is true.

During the day, when the air is hot, some terpenes may evaporate or be damaged by UV rays, but during the night time, those terpenes get a chance to recover and increase in number.

Darkness Before Harvest Lab Results: Are There Any?

There is one specific study on this front that many sources refer to, a study performed by the Stichting Institute of Medical Marijuana.

Now, let’s keep in mind that while this is a real organization, finding the actual study is not possible. This study, performed by James Burton, the founder of the institute, had half of the plants harvested in the light and the other half after a 72-hour darkness period.

The results showed that the plants harvested in the dark could potentially have up to 30% more THC than those harvested in the light. Although this does admittedly seem unlikely, there are plenty of sources out there that talk about this study.

There are also some independent studies out there conducted by normal growers. One study showed that a strain of Pacific Punch has 19.8% THC before a three-day darkness period, and 21.9% THC when harvested after a three-day darkness period.

The same can be said for the Runtz strain, which saw the THC increase from 16.9% to 17.6% after a three-day darkness period.

Conclusion: Should I Harvest In The Dark or Light?

The bottom line here is that you should definitely harvest in the dark. Although the evidence is not 100% there, it is safe to assume that having a darkness period of at least two days prior to harvest may increase both THC and terpene levels in your weed.


My passion for the sticky icky started nearly a decade ago, and it all began when I first laid my eyes on the beauty that is the marijuana plant.

I cover all aspects of growing from equipment recommendations to plant health/care tips to help both new and experienced growers.