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Flushing Cannabis Plants

Last updated: 20 August 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 Your Cannabis Plants 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. The same goes for those strains that taste absolutely amazing. Needless to say, flushing your cannabis is critical.

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What Is Flushing?

Flushing is basically exactly what it sounds like. Flushing marijuana plants before harvest 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, 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 H20 at the end of their lifecycle.

When Do You Need To Flush Your Cannabis?

Flushing cannabis plants is important for a few reasons and isn’t necessarily limited to harvest time. The following are three different instances where flushing cannabis 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 than those they need when they begin to flower. Flushing your cannabis plants when you make nutrient changes helps to remove any of the veg nutrients still present in the soil. Flushing 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 flush 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 out of 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 your marijuana 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 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 flush too early and you don’t want to flush too late.

when to flush cannabis plants

So, when’s the best time? It all depends on the medium you’re growing in.

  • Soil: When growing in soil, flushing cannabis plants 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 cannabis 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 flushing 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 cannabis is one of the simplest and easiest parts of the growing process. When you would normally feed them nutrients, simply give them 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 1300ppm. You’ll want to keep flushing until these numbers drop to 50ppm, 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 than 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 in your hydroponic setup when giving them 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 hydroponic 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 you plan on harvesting.

When Not To Flush Your 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 amended 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.

Cannabis with a perfectly pure and natural taste is that which has been properly flushed. Not only does it taste better, but it tends to smoke a lot smoother as well.


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, flushing 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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