Flushing Cannabis Plants

Last updated: 9 February 2020

flushing weed

When it comes to growing weed, there are a few things you can do to ensure a successful harvest once plants have reached maturity. Flushing your weed is one of them. If you’re new to growing ganja, “flushing” is a term you might not be familiar with, but doing this before harvest is an integral part of the process.

Why Flushing Is Important?

Flushing your cannabis plants can make a huge difference in the quality of your harvest. If your goal is to grow the best buds you possibly can, you’re definitely going to want to flush your plants before harvest, as this can make or break the quality of your crop.

If you’re like most cannabis connoisseurs, you likely enjoy a smooth smoke that tastes amazing – and if you’ve ever smoked any of those perfect buds where the smoke glides effortlessly into your lungs on the inhale, it’s safe to say the plant was flushed before harvest.

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What is Flushing?

Flushing is basically exactly what it sounds like. It involves taking a significant amount of water without any nutrients and running it through the soil your plants are growing in.

flushing weed plants

Most growers typically flush their cannabis plants for a few days up to a couple weeks before harvest. The process itself is simple; every time you go to water your plants, use the same amount of water you would normally add your nutrients to, but don’t add any nutrients. Flushing is simply giving your plants nothing but good old-fashioned H2O at the end of their lifecycle.

When Do You Need To Flush Cannabis?

Flushing marijuana plants is important for a few reasons and isn’t necessarily limited to harvest time. The following are three different instances where it becomes critical.

When Implementing Nutrient Changes

During its lifecycle, cannabis requires different nutrients. The nutrients your plants need while growing in their vegetative stage are different from those they need at the flowering stage. Flushing your cannabis plants when you make nutrient changes helps to remove any of the veg nutrients still present in the soil. It is a great way to “reset” the soil and start fresh with brand new nutrients best for your plant’s next growth stage.

When Nutrient Lockout Occurs

While nutrients can help cannabis plants thrive, too many can lead to nutrient lockout. Nutrient lockout is when plants can’t access the nutrients you feed them. This can occur from overfeeding, inaccurate pH levels, and other stresses like salt buildup in your soil. Flushing cannabis when nutrient lockout occurs helps to wash out excess buildup in the soil, allowing the plant’s roots to once again absorb the nutrients they need.

Before Harvest

Flushing before harvest is something most experienced growers do with each crop. Why? Because flushing nutrients from the soil forces the plant to use the nutrients that are stored within until plants are cut down to be cured. Many attest that flushing before harvest results in higher quality buds and a smoother smoke. Flushing is also said to make cured weed taste better, without that “chemical” taste that can occur when the soil is still full of nutrients come harvest time. Flushing plants before harvest will lead to a much higher quality product after harvest, which is typically the goal of any marijuana grower.

Tips for Flushing Marijuana Plants Before Harvest

when to flush cannabis plants

When exactly should you flush your cannabis plants to ensure you’re reaping the best possible harvest? This is a great question, as flushing your plants at the wrong time can ultimately result in a lower quality product. You don’t want to do it too early or too late. So, when’s the best time? It all depends on your grow medium.

  • Soil: When growing in soil, flushing should occur about two weeks before harvest. Check your trichomes. When they start to turn from clear to cloudy or milky is a good indication of when to start flushing your plants. These cloudy, milky trichomes are the ones that contain the most THC, and when approximately half of the trichomes on your buds begin to turn milky, this is a good indication that harvest time is close. Flushing plants too early or too late can seriously impact the quality of your smoke, so paying attention to trichomes can indicate when they’re ready to flush.
  • Coco/Rockwool: When growing in coco or rockwool, flushing marijuana plants should occur approximately one week before harvest. Why? Because coco coir and rockwool don’t hang on to a bunch of extra nutrients. Just flushing them 2–3 times before they’re ready to harvest should be sufficient to remove any excess nutrients they might contain.
  • Hydroponics: Hydroponic setups only need to be flushed for a couple days, and this is a lot easier than washing out nutrients from soil, coco, or rockwool. All growers need to do to flush plants grown hydroponically is drain the water in their system and refill it with fresh water that’s properly pH-balanced.

How to Flush Cannabis

Flushing marijuana is one of the easiest parts of the growing process. When you would normally feed them nutrients, simply give them plain water instead. Depending on your setup, this means that for the last one to two weeks of your plant’s life, all you want to give them is pH-balanced water.

When watering, flush your plants with as much water as they can hold. Let this water slowly drain through the soil and then flush the plants again. While doing so, be aware of the color of the water that’s draining from the bottom of your pots.

When you start the flushing process, this water will be dark and look dirty. You’ll want to continue to flush your plants until the water that drains out of your pots is as close to the same pure, clear water with which you’re flushing them.

trichomes ready to flush

One way to ensure your flush was a success is to use a TDS (total dissolved solids) reader that will let you know just how pure the runoff water really is. When first collecting the runoff water, you’ll likely find that TDS levels are as high as 1300 ppm. You’ll want to keep flushing until these numbers drop to 50 ppm, or as close as possible to the TDS of the water you’re using to flush your plants. A TDS reader makes gauging flushing much more accurate than doing it by eye.

Some growers choose to flush plants with water and molasses. Why molasses? It’s said that doing so helps add incredible flavor and aroma. You don’t need much, though. Only 1TB of molasses per gallon of water is recommended for about a week before harvest instead of a straight water flush. While some growers swear by a molasses flush, it’s not necessary if you don’t want to do it.

How to Flush Hydroponic Plants

how to flush hydroponic plants

As we mentioned, flushing hydroponic plants is different from flushing cannabis plants grown in soil or coco. When flushing your hydroponic setup, simply drain all the water out of your reservoirs and refill them with properly pH-balanced water that doesn’t contain any nutrients.

What’s the proper pH level to give plants during their final flush? Go for a pH level of 5.5–6.5 and your plants will respond in thanks by offering a harvest to be proud of.

Mineral salts also work well in such setups. Simply add these large mineral particles to the water you’re flushing with, which work by pulling out extra minerals that have been deposited near the plant’s roots.

Keep in mind that flushing hydroponic cannabis plants should only be done for a few days before harvest.

When Not to Flush Cannabis Plants

how to flush soil before harvest

There is one instance where you won’t need to flush weed. This is when you’ve grown your plants in soil that’s already had nutrients added to it. Amended soil is designed to offer all the nutrients your plants need during the entire phase of its growth. If you flush cannabis plants that have been grown in amended soil, it can disrupt the perfectly-maintained nutrient balance that such soils contain.

What Results Does Flushing Cannabis Offer?

If you’re growing weed, chances are you want it to be the best weed it possibly can. You’re not growing to harvest some subpar smoke – you’re growing to harvest some serious high-quality buds. Here’s where flushing comes in handy.

It’s said that flushing cannabis allows for a higher quality smoke in the end product. Most growers flush their weed plants to improve the taste of their buds once they’re cured. If you’ve ever tasted cannabis that was slightly “chemical”-tasting, it’s likely because the plants weren’t properly flushed. When too many nutrients are present at harvest, it can significantly affect the taste of your buds.

Experience growers who flush their plants eventually get a perfectly pure and natural taste. Not only does such weed better, but it tends to smoke a lot smoother as well.

Debate and Discussion: Is Flushing Worth It?

Over the years, cannabis flushing has gained significant popularity among growers who consider it to be a crucial part of their cultivation process. However, there is also an increasing number of growers who believe that recent studies indicate that cannabis flushing has no impact on the residual minerals in the plant, nor does it enhance potency. Surprisingly, some recent studies even suggest that unflushed cannabis actually has a better taste.

Recently, there has been a concerted effort to delve deeper into the topic of cannabis flushing in order to comprehend its effects and determine if it provides any scientifically measurable advantages. Given the substantial investment in the legal, licensed cannabis cultivation industry, there is a rising scientific interest in gaining a better understanding of the process of flushing.

RX Green Technologies, a company specializing in nutrients, conducted a study using identical cannabis plants that were grown in a uniform manner but were given different flushing durations at the end of their blooming stage. Certain plants were not flushed at all, while others were flushed for either 7, 10, or 14 days.

According to the findings, there were no significant patterns or tendencies observed in terms of yield, terpene content, or THC levels that exceeded the margin of error in the experiment. This may come as a surprise to those who advocate for flushing, especially as the taste potency and yields of the cannabis plants were not noticeably impacted in either direction.

After the laboratory conducted tests on the buds, they were later passed on to a smoke test team for an impartial evaluation based on various factors. In general, the team did not notice any significant statistical patterns. Interestingly, when it came to flavor, almost half of the respondents (47%) rated the non-flushed weed as 'Good' quality. Furthermore, buds from the non-flushed marijuana plant received the highest 'Great' rating, as reported by 16% of the respondents.

Final Thoughts

While it’s true that weed really does grow like a weed, there are certain things that can be done during the process that will yield a higher quality harvest. Flushing marijuana plants is one of them. If you’re interested in harvesting the highest quality, best-tasting, smoothest cannabis you can, this is a vital part of the process.

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I have flushed and I have not flushed. Flushing is better. Did I sacrifice a few grams to make my smoke better? I don't care, because I made my smoke better. I am not a drug dealer, legal or illegal, so this is not a 'for profit' endeavor for me. I want the best quality I can grow, and yes, I can grow better than I can buy, and yes flushed pot tastes better then not flushed pot.
So many times I heard flushing is bs or with each flush you lose grams. But I agree with you. If you have good smoke, you have a good method. That’s all that matters
Appreciated! Very useful info.
I flush 2 weeks out because i use synthetic nutrients and have read horror stories of the weed snap, crackle, pop when burned and produces a thick, black ash that easily clogs screens. I just don't see the need to chance it. Organics does not require flushing as i understand it.
Very good, i had seen a similar article before touching the same topic. But this was very good. The science fits with my own understanding and I believe flushing to be truly beneficial. Thanks.
Here’s my take on flushing... if there is a lot of nutes built up, from overdoings it while feeding, the flush may even out the ph some and help the plant recover to a healthier state to finish strong. I do flush, well not actually flush flush, I don’t run any extra through the pots, I just give water for the last half week or week. I’ve been moving away from that and just cutting down the nute doses instead, as I want to plump them up as much as I can at the last week. I think if synthetic nutes are used, very nasty chemical crap, just water for the last week or a flush would be beneficial. This is just what has been the conclusion I have drawn from this site.
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