Flushing Cannabis Plants: Is It Necessary?

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Added 16 December 2022

Flushing is a topic of debate for more than a decade among cannabis growers. While some growers flush their plants to remove excess nutrients collected over time in the soil, others prefer not to as they consider it a futile effort. 

To flush or not to flush — that is the question. 

In this topic, we will cover everything necessary about flushing. What is flushing, is it really necessary, and why do growers do it? 

Dig in…

What is Flushing Cannabis Plants?

What is Flushing Cannabis Plants?

Flushing, as the name implies, involves using water in large amounts to flush out all excess nutrients in the soil. In other words, you’re cleaning the soil and removing residuals just before harvesting your precious plants. 

The common idea associated with flushing is that it improves the quality of the buds. Many growers stop feeding their plants at least a week before harvest. At the same time, they introduce lots of water (often twice or thrice the container size) to the growing medium to eliminate excessive nutrients. 

Why do Growers Flush Cannabis Plants?

Why do Growers Flush Cannabis Plants?

As mentioned already, some growers flush their plants whereas some feel it’s a waste of their time and resources. Plus, it makes sense to think that the plant has already absorbed necessary nutrients and it wouldn’t matter if you remove it or not a few days before harvest. 

It was pretty simple earlier to grow cannabis plants. Pop a few seeds, water the plants, fertilize and then harvest them according to the climate. 

However, with the advent of technology, new terms, techniques, equipment, and even better versions of cannabis strains, growers have adopted new ways, and flushing is one among them. 

Growers flush their cannabis plants in the hopes that they will let go of any nutrients stored in excess. Why? Because excessive nutrients can reduce the quality of the buds by hampering their taste and smell. In addition, the buds can be harsh and give you coughing fits. Growers also believe that buds of plants that haven’t been flushed turn black or charred once you light them. 

Today, almost every grower flushes his plants, although there’s no concrete evidence behind it. That said, almost every aspect of the cannabis industry lacks research, but we still experience the benefits of cannabis and use it, don’t we? 

Coming back to the topic of flushing, we can argue till dawn but still fail to conclude. This is because flushing is mainly based on personal experience. 

Methods of flushing vary from one grower to another, depending on their experience in the past, and, of course, preference. While some people tend to use chemical agents meant primarily for flushing, others use plain water. Whatever the case, flushing is pretty common in the industry and many commercial operations also indulge in it. 

How to Flush Cannabis Plants?

How to Flush Cannabis Plants?

Flushing your cannabis plants is a straightforward process. Typically, you wait until the plants are almost ready to be harvested. However, you need at least two weeks for the flushing to work. 

Many growers use flushing agents that aid in keeping the salts and nutrients in a soluble state, but it’s completely fine to use plain water. Just ensure that you adjust the pH between 5.8 to 6 or you’ll end up with pH problems at the very end of the plant’s flowering cycle, which isn’t good news. Maintaining the right pH is critical as it helps the nutrients dissolve in the water without any issues. 

So, whether you’re using a flushing agent or plain pH-adjusted water, and assuming that the plant has about two weeks before harvest, you’re ready to flush the plants. Next, it’s time to run the water through the plant’s growing medium, which is essentially called flushing. 

Flushing is just like watering, only you do it in excess. Flush the plants until the water starts draining out through the drainage holes. Typically, if you’re using a 3-gallon pot, for instance, it’s best to start with 3 gallons of water, but it’s not uncommon for growers to use 6 gallons during the flushing process. 

Some even go as far as using five times the size of the container, which means they use 15 gallons of water to flush a plant growing in a 3-gallon pot. 

The amount of water you use depends on your previous experience. If you find that flushing hasn’t helped your buds, you can get away with not flushing the plants, just like organic growers. However, if you feel that the flushing has helped, you can continue doing everything that worked for you previously. 

It’s a good idea to collect the run-off water and test the pH to ensure everything is fine. If the pH is way too off, you will need to repeat the process until the pH returns to its normal range again. As you flush the plants, you’ll notice that the EC and PPM will begin to drop slowly. 

You run the risk of overwatering the plants, so you’ll have to be precise and keep the fans running full tilt to let the water dry out. If you’re growing outdoors, though, it’s not much of a problem as the wind will take care of it. You can wait for the plants to dry and repeat the flushing process to ensure the plants aren’t overwatered too much. 

In addition, flushing usually makes the plants lose their green sheen and turn yellow and pale. This is pretty normal, and there’s nothing to panic about. Even if you don’t flush, the plants will look pale and yellow during the final stages of flowering. 

As you flush, the nutrients are eliminated from the soil and the plant will resort to using the nutrients it has stored. At this point, the plant will transfer its mobile nutrients to other parts such as the buds to keep them safe and healthy. 

It’s important to note that flushing doesn’t remove nutrients from the plant; instead, you’re only eliminating excessive nutrients from the soil. Many people harbor a misconception that are removing the nutrients from the plant itself. However, it’s not possible to remove the nutrients collected in the plant because once the plant absorbs the nutrients, they will remain there no matter what you do. 

How Long do you Flush Cannabis Plants?

How Long do you Flush Cannabis Plants?

Many growers think that it's beneficial to flush their cannabis plants for long periods. The common consensus is that the more you flush, the better and smoother the smoke. It's also believed that the buds from flushed plants turn into white ash when you burn it compared to black charred ash with non-flushed plants, which inevitably means that they tend to be harsher on the throat.

Why do growers think that non-flushed buds are harsh and pop and make weird sounds when you smoke? Well, it's believed that the excessive nutrients stored in the plants or buds cause the problem. However, there's no evidence to support this claim, but since there's no plausible explanation, it's generally accepted to be true. 

For many growers, flushing the plants produces a smoother and well-rounded smoke compared to buds that aren't flushed. In addition, you can flush the plants up to any period although many growers stop after using twice or thrice the amount of the container. 

They also check the pH to ensure it's all good. But, one could argue that the trick lies in curing the buds properly. No matter how well you flush the plants, they will taste harsh if you don't dry and cure them appropriately. Therefore, for some growers, flushing could be an exercise in futility.

Should I Flush my Cannabis Plants?

Should I flush my cannabis plants?

As mentioned already, many growers flush their plants and it's considered almost mandatory now. However, some studies differ.

For instance, a study conducted by RX Green Technologies in 2020 had a cannabis taste test. First, they had a dispensary grow a strain called Cherry Diesel and flushed the buds with varying periods (14,10 days, and 1 week). 

Then, they mixed some regular (non-flushed) buds along with them to increase transparency and had many experts from the cannabis industry test the taste. They were even asked to rate the smoke quality, flavor, and color of the bud after lighting it up.

Ultimately, nobody could differentiate between the flushed and non-flushed buds and many guests actually preferred the non-flushed buds that were fed with nutrients till the last day of their harvest.

Although this is just one study, it goes to show that flushing may not be necessary. That said, other strains may taste better if you flush them. In addition, nobody else reviewed the study and they haven't revealed the data or methods they used to come to conclusions.

Deciding whether to flush your plants or not is up to you. If you've had success with it before, you can continue doing it.

Your decision to flush will also depend on the type of growing medium you've used. For instance, flushing organic soil is unnecessary whereas a Coco medium may need some flushing. Basically, any medium that doesn't retain too many nutrients won't need flushing.

In addition, if your plant has been struggling with nutrient deficiencies, you may as well leave it alone as flushing may hamper its delicate balance. Also, if the medium isn't draining appropriately due to too many clumps or other issues, your best bet is to avoid flushing and just let the plant finish its cycle.

At the end of the day, rely on your intuition and give your plants a proper flushing if you've had great results with it. But it's also okay to not flush it if you aren't too keen.

Summary: Flushing Cannabis Plants: Is It Necessary?

Flushing cannabis plants is a norm and nobody knows when and how growers began using the technique. Although it has worked for many growers to produce smooth buds with a mild taste, others feel it is unnecessary. 

We still need proper studies on this topic to conclude whether flushing holds any importance. However, until then, you can rely on your experience and flush the plants if it has worked for you in the past. 




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Flushing is for toilets !
I flushed 1 plant and not the other, we'll see what happens.
@PottyMcCannabis, do not forget to let us know please 😊
@Rams3s, not really. It looks and smell the same to me and to my wife who doesnt know i'm doing this test. Still not scientific but we'll see.
@PottyMcCannabis, do you already see something ?
Study shows diagrams that there is no really change flush or no flush when they measured chemical compunds from buds. Tried many ways too but didnt notice any change. I just drop ec little bit 1-2 week before harvest but never just plain water anymore. 😊