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Does ICE Water And Full Darkness At The End Of A Grow Increase Trichomes?

Added 8 April 2021

Introduction :

Cannabis is probably one of the only plants ever to be cultivated for its trichomes. In the culture of cannabis growing, there are many types of growers that seem to be using an almost infinite amount of techniques and tricks to increase the production of trichomes in their fields of happiness! This goes from "low or high-stress training" to "hydric stress" and so much more. Basically what the grower does is simulate situations occurring in nature to be able to manipulate the plant in a beneficial way, to create a better and bigger harvest with more potent buds. In this article, we will be taking a closer look at the use of ice and ice-cold water flushing at the end of the flowering period, with a period of full darkness, usually around 2-3 days or even longer up to 7 days, just before the harvesting.
Does it make sense? Is there any scientific evidence backing this tactic with the purpose of stronger and more potent buds???

After taking a first look at the subject on different grow forums, including our Growdiaries platform, the claim seems to be defended by sum and fought off by others ( and both camps have reputable growers defending it! )

The idea behind the technique

Trichomes on cannabis plants are a natural defense mechanism to defend these plants from harmful light such as UV-B, but it is also a deterrent for insects and other infestations. It is especially in the later stage of the flowering period that these trichomes develop fully. In nature, there will be a moment, when autumn starts coming in, that the outside and water temperatures start to drop in the environment and the amount of exposure to sunlight starts to drop because days get shorter.

So what we are doing with "ICE-flushing" and adding a"period of darkness" is giving our plants a form of shock therapy and at the same time flushing the medium and plants, in order to force the plants to make a final-ditch-effort in producing extra trichomes.
There are growers that put ice straight onto the soil, some use ice-cold water, others have climate-controlled growing spaces to make the temperature drop, by doing it in this manner there will be less risk of damaging the roots or shocking the plants too much. Others even add an extra UV-B bulb to their installation!
When it comes to the flushing itself, many have their own schedule but most apply around 14 days of flushing before harvest and dispersed over that period there will be moments of using the "ICE" method to shock the plants in that final timeframe of their lifespan.

As with many tricks and techniques in the cannabis industry, because of a lack of scientific research, there is not always a lot of info to make our final conclusions whether there is truth to be found in the real science behind some of these.

Is there evidence to this theory?

As stated before, trichomes are a plant's 'sunscreen'. This gets produced most in its dark hours to get itself ready for the sunrise, and at the late flowering stage this reaches a maximum and that is what we are looking to manipulate. By extending these dark hours we give the plant a longer window to produce this.
Of all the claims out there that can be related to this technique, one of the best-founded facts to add to the argument, is the following :
The Stichting Institute of Medical Marijuana (SIMM), was the first company to sell cannabis through pharmacies in Holland. They have been investigating the medical possibilities of cannabis, together with TNO laboratories and the University of 'Leiden'.

"One of their discoveries has been that to keep the ripe plants in the dark before harvesting could ( not will, but COULD ) increase their potency. SIMM's growers separated a crop of mature plants, harvested half of them and kept the other half in absolute darkness for 72 hours before cutting and drying them. The analysis of the resulting dried buds showed that some had seen an increase of THC of up to 30%, while CBD and CBN remained the same."

In the book "Cultivating Cannabis", published in 2010 and written by C.K. Watson, you will find this statement on page 238 :

"There's a rumor going around that when you put your plants in darkness for 36 to 48 hours before the harvest, this will result in a higher concentration of trichomes. The myth is further enhanced by growers saying it has worked for them. This has been tried on 30 different strains, with the result that only 4 out of 30 strains showed a marked higher concentration of trichomes, while the other 26 strains began to hermaphrodite and the buds looked malformed."

Risks behind using this technique 

As with many tricks, there comes risk! Putting your lovely cannabis plants under too much stress can always lead to a failing harvest and at such a late stage, should we really risk our crops? To what mostly relies on the growers' community's own opinion and experience with very little scientific research to back these claims, we must be aware that when experimenting with a technique like this, there can be bad consequences :

  1. Root damage: especially with using cold water or ice on top of the soil there is an increased chance of root damage because of the sudden temperature drops, therefore it is much better to have a climate-controlled growing space to simulate this temperature change
  2. Hermaphrodite/malformations: with the extended period of darkness at the end of the flowering stage there are growers that run into the problem of when risking it too long and misjudging the right harvest moment that the buds develop hermaphrodite signs and have malformations, this is something that comes with experience, patience, and knowledge of the strains you are growing to get this moment perfect!
  3. Rotting flowers/buds: because of the drop in temperature and the lack of light for an extended period with bud size at maximum there is a higher chance of developing bud rot at this late stage, therefore if you apply this technique, make sure to have a well-ventilated space and keep a good eye on your humidity levels


As is often the case with growing techniques for cannabis there is a lack of information! Luckily, there is a massive community out there of forums and blogs such as our own Growdiaries, where many intel can be found to guide you on what is best! It is there where the debate continues whether this is a working technique or not, and because this subject needs much more investigation, we cannot put this aside as true or false. Having a successful grow depends for a big part on the genetics of the plant, but also on the environment that they grow in. With growing the right strain with strong genetics under the right circumstances they will flourish! And a good grower with the right amount of experience will be able to tell the perfect moment for harvest, with or without the use of these techniques!

If you found this article useful or have any experience in using this technique or have more data to back the claims, please drop a line in the comment section below!


Leiden University - Scholarly Publications

Can Ice Water And Full Darkness Increase Trichome Production In Cannabis? Steven Voser ( 2019 )




Why anybody would want to stress their plants, in any way, right before harvest and after weeks/months of careful growing, is beyond me!
Ice cubes are crazy and extended darkness will just cause the plants metabolism to slow severely, possibly leading to trichome degradation, not enhancement, and I personally can't see how these "techniques" would be of any benefit, in any way. Myths like these, made up by people who are too high to think clearly and possessing a basic lack of knowledge about how plants function, need to be taken with a grain of salt.
I will never try these "techniques", but to each their own.
If these things were true and did what they supposedly are able to do, breeders/growers/scientists would have been advocating for these types of manipulative stresses decades ago, and all backed by conclusive evidence. As such, myths like these, and the myth about the application of molasses, as well as the myth of growing 24/0, should all be buried and thought of as jokes, made up by those with limited intelligence.
Like I said earlier, why anybody would want to stress their plants in any way, right before harvest and after weeks/months of careful growing, is beyond me.


Hermaphrodite/malformations: It takes weeks for this sort of cell differentiation to occur. Anything done in last few days is zero risk of seeding your plants. Anything that grows out in that time period was caused long before you see them, or genetic but still long before you see them and never overnight.


Trying to mimic nature indoors. Ice on a few liter pot, may be of 5 o 50 liters, does it matter? How come nobody simulates a wildfire? Should be enough stress to sky rocket the Thc, right? What happened with _a little_ foliar spray in the morning, to mimic dew ? Whiping the leaves with _a little_ beer? Do _a little_ dance, make love, get down tonight :-) ?


load of shit! dark period burns up carbs and improves the cure, ice cubes is stupid bullshit grow you plants with love and care if you want quality. you cant save shot weed with magic techniques



You just hit the nail. Bro sience, good one,:sweat_smile::sweat_smile:!

I like your reasoning, learn the progress of the crop. It will get you good buds . Rest is just adding minimal percentages in my opinion. Like you said, plants dont just change overnight.



@TILLBILL, The darkness is more about 2 competing rates. One is trichome production, and the other is evaporation/degredation from the environment over time. Studies have shown that 48 hours is optimal. Proper methods of isolating and measuring very likely employed based on source of information.

This stuff is all measureable.. it would simply take a suitable sample size, methodology and few studies to prove it is repeatable cause and effect.

I've never read anything on the ice treatments. I woudln't do that based on anecdotal evidence alone.

Even if the differences are statistically significant, they are likely small changes overall when given time frame of each "technique". So, no one should feel left out in the meantime if they don't do one or the other (*money is on the light deprivation beingn real* great odds...) before we get some competent research in these areas and not rely on bro science and what someone "saw on 3 plants one time."


Instead of darkness I’ll keep stacking in the light until harvest. If this dark period theory has any benefit. Then it’s because you mimic nature’s effect as days shorten. So instead of setting up a mold factory at the end why not try decreasing the light period by 30 min in the last week or 2 . If the theory is to mimic what causes buds to get dense and sparkly then do that, maybe. But no way ice or that much darkness can produce a benefit that would outweigh the risk.

Forget stressing the plant for that final few days, it would stress me worrying about screwing up a completed grow. Yikes , no thanks


Only mold grow in the dark pass 24h...
Maybe 24h good so the plant get rid of carbs in the plant and grow a little more trichomes and leaves during that time using the car s left over.... I guess 24h darkness is enough!


when the ice turn into liquid it eventually evaporate and that would increase the humidity dramatically. You can expect what gonna happen if you don't do it correctly right?


I recently harvested and tried the 3 days of darkness...never tried the ice method.


Thx a lot my friend..:wink:


Good read

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