There’s a rumour circulating around the cannabis community that a combination of ice water flushes and a total dark period of 24–36 hours just before harvest can greatly improve your plant’s trichome production and potency. Some growers claim this is one of the best ways to enhance the quality and potency of your bud; others say it’s total BS.

As is often the case with cannabis grow topics, most of the information available about ice flushes and prolonged periods of darkness is hearsay. In this article, we’ll explore the information available on these techniques and how they might affect trichome production in cannabis.

THE CLAIM: ICE WATER FLUSHES + TOTAL DARKNESS IMPROVE TRICHOME PRODUCTION

The theory behind this technique is simple. First, the ice water flushes are meant to expose your plants to lower temperatures, which can often bring out more appealing hues in your buds. Many growers do this already, simply by bringing down the temperatures in their tent or grow room using air-conditioning or fans. Here, the only difference is the temperature is brought down using the cold water flushes, rather than an air conditioner or ventilation system.

Secondly, the prolonged periods of darkness are supposed to stress the plants. In an attempt to protect their flowers and maximise their chance of reproducing, the plants use nutrients from the fan leaves to keep their buds growing. Together, the combination of cooler temperatures and less light should encourage your plants to grow bigger, denser buds with a higher amount of trichomes and peculiar colours.

We also know that particular kinds of stress can push cannabis plants to reach their maximum potential. Supercropping and splitting, for example, are two common grow techniques that rely on extreme levels of stress. Nonetheless, putting your plants under light stress so close to harvest can be daunting. After all, if something goes wrong, you run the risk of potentially losing your entire harvest.

THE VERDICT: DOES IT WORK?

Unfortunately, there’s very little good-quality information out there on the effects of prolonged darkness and ice water flushes. Most of what we have to work with are posts of “home experiments” published on grow forums like 420 Magazine, THC Farmer, and more. And the little information we do have available is contradictory; some growers report great results while others say exactly the opposite.

In 2013, a grower posted in 420 Magazine’s “The Grow Room” forum. The grower was working with a Rascal OG plant, which they flushed with ice water and held in complete darkness for five whole days prior to harvest. The grower also compared the ice water flushing technique to regular flushes using a combination of water and molasses, which were given to the plant in a grow tent under regular lighting conditions. They then administered the final flush under complete darkness. They were originally only going to hold the plant in darkness for about 48 hours.

The grower noted that the period of darkness made significant changes to the amount and size of the trichomes on the plant’s buds. “I'm not sure exactly what is happening through the whole botany aspect but I saw the trichomes actually bulk up in length & width, with a few (not too significant) turning yellow/amber in colour”, they wrote.

They did state, however, that they were sceptical of using the ice water method, and would recommend just using regular room temperature water to flush plants in complete darkness.

In one of his weekly grow updates, Mr. Grow It explained why he gives all of his plants 48 hours of complete darkness before harvesting. He explained that most of the resin production during flowering happens at night, and that exposing his plants to extended darkness served as “one last-ditch effort” to boost the plant’s resin production. He also noted that light actually degrades trichomes, and using a period of prolonged darkness can prevent this degradation, which presents itself as milky or amber trichomes. Mr. Grow It makes no mention of using ice water flushes in his video.

Some forum posts also claim that the Stichting Institute of Medical Marijuana (SIMM), one of the first companies to sell medical cannabis via Dutch pharmacies, used this prolonged darkness technique to enhance the potency of their strains. SIMM was rumoured to have separated a batch of their plants, harvesting half and leaving the other half in 72 hours of complete darkness before harvesting. Together with TNO laboratories and the University of Leiden, SIMM tested the potency of the plants and found that those left in 72 hours of darkness contained up to 30% more THC than the other batch. However, we weren’t able to find any information on SIMM or this study via our research.

And while the prolonged darkness technique definitely has its fans, it also has its critics. Many growers claim that cannabis plants are unable to produce more resin in just 24–48 hours, and that the prolonged darkness technique does little more than just delay your harvest. There are also growers who believe the plants need to be left in darkness for multiple days in order for them to see any noticeable changes in their resin production.

Unfortunately, there is hardly any scientific literature on growing cannabis. That means growers are often made to rely on their own instincts and tips/tricks from other, more experienced growers out there. If you’ve ever read through some of the posts on cannabis grow forums, you’ll know just how divided the community can be on some topics. This is no different, and it’s really up to the individual grower to trial this technique and evaluate the results for themselves.

			Written by: Steven Voser Steven Voser is an Emmy Award Nominated freelance journalist with a lot of experience under his belt. Thanks to a passion for all things cannabis, he now dedicates a lot of his times exploring the world of weed.
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