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What to Know About Flushing Cannabis

Updated August 21, 2022

Flushing is one of the many steps that you should pay attention to when growing your own cannabis. Flushing is crucial to maximizing your results and is relatively straightforward once you know what to do. For most people, the most challenging part of flushing is determining when to do it.

To ensure you have all the information you need to flush your cannabis plants properly and at the right time, read on.

Defining Flushing Cannabis

Before you can begin to understand the importance of flushing and how to do it, you need to understand what it means. To keep things simple, flushing refers to removing any leftover nutrients in the soil where your cannabis plants are growing. This process is done with pH-neutral water.

By flushing your cannabis, you let the plants and soil start fresh, without an excessive accumulation of nutrients.

Why Flushing Cannabis Matters

At first, it may seem counterintuitive to flush the nutrients out of your cannabis plants’ soil. In reality, this is a necessary step to help the roots of your cannabis plants absorb the nutrients that remain.

To put it differently, flushing will “starve” the plants, encouraging them to absorb any additional fat that remains, so it can be used for energy.

Improves the Buds’ Smoothness

Flushing cannabis before you harvest it will give the buds the push to become higher quality and smoother. This way, you do not have to worry about throat irritation or coughing when you smoke them. If you smoke cannabis that is not very smooth, it likely was not flushed.

Improves the Taste

Most people flush their cannabis primarily to improve the taste once it is cured. The chemical taste that is common among cannabis occurs if the grower did not properly flush it. That taste is the result of too many nutrients present when harvesting took place. Flushing at the right point ensures that the only taste is the cannabis itself, no chemicals or other nutrients. This is smoother.

Curing Alone is Not Enough

Some people will argue that you do not need to flush your cannabis if you plan on curing it carefully at the end of the harvest. After all, there are ways to cure cannabis that will make up for any chemical taste.

However, this type of curing will not be 100 percent effective. For the best results and the clean cannabis taste that you want from your buds, you should flush and then cure. Think of curing as a backup that will let you fix some of the smaller mistakes you made during flushing.

Why Timing of Flushing Cannabis Matters

The timing for flushing is crucial because you want to do it while there is still enough time left before harvesting for your plants to take advantage of the flushing to thrive. At the same time, you need to make sure there is not too much time left before harvest, as that could lead to the plants becoming unhealthy.

Bad Timing Can Hurt the Plants

If you time your cannabis flushing poorly, this can produce serious negative consequences for your plants. Incorrect timing can actually hurt your yield.

When to Flush Cannabis

Since the timing for flushing cannabis is so important, you want to make sure you understand the ideal time.

In most cases, it is best to flush about two weeks before the harvest. Keep in mind that depending on your grow setup and strain, this may vary slightly.

Timing the Harvest

Since the typical best time to flush cannabis is two weeks before the harvest, you need to be able to judge when to harvest your cannabis. The trick to determine this is to pay attention to the trichomes on the plants.

Examining the Trichomes

The trichomes will let you know not only when to harvest your plants but also about when to flush them. At the time of flushing, your plants should ideally still have trichomes that are mostly clear, with just some that are white or milky white. Or, look for trichomes that are starting to transition from clear to milky and cloudy.

Ideally, two weeks after you flush the cannabis, the trichomes will have changed their color already.

Important Variations Based on Setups

As mentioned, the overall setup and the growing medium you choose will affect when you should flush your cannabis.

If you are using amended soil, for example, then you should not flush the plants at all.

If you use coco for growing, then flush the plants around a week before the harvest occurs.

If you are growing with hydroponics, flush a few days before harvest.

Flushing Cannabis Can Also Serve Other Purposes

Although the main reason to flush cannabis is to ensure that it is smooth and healthy, there are also some other potential scenarios when flushing the plants will be helpful. In those cases, you will not want to wait until the harvest to flush and should instead do it right away.

Flushing Away Problems During Vegetative Growth

Sometimes, cannabis plants will experience issues due to nutrient problems during the vegetative growth stage. These include toxicity or nutrient burn. You can recognize nutrient burn from overfeeding if the tips of your plant’s leaves begin to change color and shrivel.

When that happens, it can be wise to flush the plants to clear out the current nutrients. From there, you will add back the proper nutrients in the appropriate doses.

Overcoming Nutrient Lockout

Nutrient lockout is another situation in which you will want to consider flushing your cannabis plants. This is when nutrient absorption is prevented by pH levels, salt buildup, or something else. The result is that the nutrients build up within the soil and the plant is unable to access them.

In this situation, flushing the cannabis will help remove the excess salts and nutrients that have built up. At the same time, it will restore the pH balance of the soil. The result should be your plants being able to absorb nutrients properly, so they can successfully grow.

Some people also suggest flushing your plants routinely to prevent nutrient lockout from occurring. This suggestion involves flushing the cannabis before flowering starts and then again halfway through flowering. Just keep in mind that flushing requires a great deal of care, as it can stress the plants and may take away nutrients. As such, suggestions as to whether to use flushing to prevent nutrient lockout are mixed.

Be Sure Before Flushing

If you suspect that your cannabis plant is experiencing nutrient burn due to overfeeding, you should make sure that this is the issue before flushing your plants.

You Can Flush Before Changing the Nutrient Schedule

Another option is to flush the cannabis before you change its nutrient schedule. It is not necessary to complete this type of flush, but it does not hurt. Flushing at this point essentially lets you zero out the nutrient content before you start adding new nutrients into the mix, so you can start with a clean slate and not worry about existing nutrients combining with added ones to result in overfeeding.

How to Flush Cannabis

With all that information in mind, how do you flush cannabis plants? Water is crucial, but you do not just soak your plants in water and hope for the best.

The Basics

Your goal is to water the cannabis plants using pH-neutral water at the same time that you would typically feed them.

Getting the Water

Depending on where you live, you may be able to use tap water for this flushing, without making any other adjustments. However, you should always check the pH of the water before using it. This is crucial because if it is not pH-neutral, it can upset the pH balance of your plants and cause other problems.

If you are growing your cannabis in soil, aim for a pH of 6.0 to 6.8. If you are growing in hydroponics, aim for 5.5 to 6.5.

The Detailed Process

As you flush your cannabis plants, pour as much of the pH-neutral water into the soil as you can. Then, wait several minutes and add more water, as this will push the first watering deeper into the soil.

If you grow your cannabis in pots, expect to see water coming out of the bottom.

Flushing Cannabis in Hydroponics

Given that you flush cannabis by pouring pH-neutral water into the soil, that method does not work for a hydroponics setup that does not contain soil.

The good news is that flushing with hydroponics is incredibly simple. All you do is ensure you replace all the water in your reservoir with your pH-neutral water that has zero nutrients.

Using TDS Meters

If you want, you can use a TDS meter, which measures total dissolved solids. Normal drained water has a TDS of 1,300 ppm. If you use a TDS meter, keep flushing the plants until the water that runs out of the bottom of the soil is just 50 ppm.

Look for Cleaner Water

If you do not have a TDS meter, you can just visually check the water that flows out as you flush your cannabis. It should keep getting cleaner.

Of course, using a TDS meter or looking for cleaner water to check the progress of flushing only works if you are growing inside and using pots that the water flows out of.

Do Not Flush with Amended Organic Soil

As mentioned, you should not flush cannabis if you are growing it in amended organic soil. This is crucial since this type of soil will already contain the specific nutrients that your plants require to thrive. If you flood that soil, you will ruin the complex ecosystem that you created within it by flushing it away.

Additionally, flushing is not necessary for amended organic soil because you always water those plants with pure water. This environment already gives the plants easy, diverse, and natural nutrient uptake.

You Can Add to the Flushing Water

Depending on your goals and comfort level, you can also add some supplements to that water that you use to flush the cannabis.

Consider things such as supplements to balance pH, beneficial root bacteria, salt leaching or clearing solutions, or blackstrap molasses, the last of which can sweeten the cannabis.

Do not add a nutrient solution to the flushing water.

Salt Leaching or Clearing Solutions

You do not need to use salt leaching or clearing solutions, but they can be a wise idea if you gave your plants a large amount of nutrients during the regular growth cycle. Do not worry about using these solutions if your plants get the nutrients right from the soil.

You Can Also Add Enzymes Later

Sometimes, you may also want to add enzymes after you flush before a harvest or to counter nutrient lockout. This is a good option if your plants are still dark green, as this indicates they likely have excess nutrients. In this case, you could add enzyme-rich formulas. The enzymes will catalyze reactions and help flush soil via the breakdown of nutrients, carbohydrates, and starches.

Other Flushing Techniques to Use

Cannabis growing experts also make use of other flushing techniques to maximize the results. These techniques can further help remove excess nutrients that are unwanted before the harvest.


Flushing will cause some level of stress to the cannabis plants’ roots. That stress means that the plants will expend more resources and energy more quickly. That use of resources and energy means that the plants use up remaining nutrients more quickly. In other words, the stress associated with flushing helps flushing progress more quickly as the plant uses up remaining resources.

Mineral Salts

You can also use mineral salts for flushing, and this is particularly helpful with hydroponics systems. To use this method, add some large mineral particles to your pH-neutral water or whatever solution you plan to use to flush the cannabis. Those mineral particles will pull extra mineral deposits by the roots. Opting for large mineral particles ensures that they are too large for the plant to absorb, so they remain outside.


Another technique is referred to as hormones and refers to quickly maturing the plant. You can add natural plant hormones to your flushing solution to speed up the maturation process of the plants.

These hormones will cause nutrients and minerals to be used up more quickly. At the same time, the solution will force the buds to ripen more quickly, increasing their potency faster. If you can harvest the plants at the proper time, you will then get a higher-quality yield.

Watch for Colors After Flushing

After you flush cannabis, you will need to pay much closer attention to the plants, particularly the coloring. Specifically, you want to look out for intense yellowing.

Slight yellowing is normal before harvesting cannabis, so that is not a concern.

However, if the leaves start turning yellow completely and it is a widespread issue, this is a bad sign. It indicates that the buds are quickly declining due to a lack of sunlight energy and you should harvest quickly.

Yellowing Matters for Appearance

Those who want harvested cannabis to look its best should also think about the yellowing in terms of how it affects the appearance of their buds. If this is a prime concern for you, be sure to harvest right when you start to see yellow on the buds or the sugar leaves around them.

Yellowing Can Happen Quickly

Keep in mind that watching for yellowing on flushed cannabis plants can be easier said than done. The yellowing can progress very quickly overnight or in a short time frame.

Look for Other Leaf Colors

If the cannabis leaves turn a color other than yellow, you do not just get to ignore this. The leaves may turn red or purple, but the buds should not follow suit. Use that discoloration as an indication that the harvest time is approaching. Once the leaves are no longer green, they cannot absorb the sunlight energy.

Other Bud Colors

If you wait too long to harvest, the cannabis buds may turn brown and feel or look crispy. This indicates that they started degrading. You will need to harvest them immediately if you notice these features, as the potency is dropping.


Flushing cannabis is an important step to take a few weeks before harvest. This process involves adding pH-neutral water to the soil and helps remove the excess nutrients from that soil. When done properly, flushing cannabis will ensure your cannabis has a smooth taste and a nice yield. You can also flush for other reasons, such as to overcome nutrient lockout. You should not flush cannabis if you have super soil or amended organic soil, but you should with normal soil, coco, and hydroponics.

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