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 :
- 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
- 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!
- 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
Conclusion
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!
References
Leiden University - Scholarly Publications
Can Ice Water And Full Darkness Increase Trichome Production In Cannabis? Steven Voser ( 2019 )
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Fast Buds
BioBizz 
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