Harvesting Cannabis

What is Flushing Cannabis and When to Use It

Flushing Cannabis Featured

You are just about to harvest with a couple of weeks left to grow and you look up how to harvest your cannabis plants and you find articles talking about flushing your cannabis plants. If you have no idea what these growers and articles are talking about, this is the article that you need to read to learn more about what this process is and how to use it to get a better tasting harvest for the best buds possible.

Flushing Cannabis

What is Flushing Cannabis Plants?

When growing cannabis, in some types of systems the minerals and nutrients can start to build up in the plants, stems, leaves and buds. This is especially true when using salt based nutrients to grow your cannabis crops. Some of the many nutrients like nitrogen can build up in your buds. 

Once harvested if these minerals are still present in larger quantities in the harvested buds. This can cause issues if you are smoking the buds either in joints or bongs. These minerals cause the buds to burn harshly and taste bad. When this happens you can normally tell the buds were not flushed because of the black ash from the joints.

Other Reasons for Flushing Cannabis

Another reason that growers will flush cannabis plants is if they have a build up of minerals and nutrients in their systems, or soil. When this happens it can move the growing mediums PH out of range or salt fertilizer build up, and cause “lockout” this is when the plant is no longer able to take up nutrients from its root system. This is another time that growers will use for flushing cannabis plants. This works by adding only plain water to the plants growing medium to remove any excess build up minerals in the medium. This will reset the medium back to a neutral state, removing the build up of nutrients and minerals that have accumulated over time. 

This can happen anytime during the growth cycle, and can slow plant growth if flushing is done for more than a few days.

How to Flush Cannabis Plants?

Lucky for growers, flushing cannabis is a very easy process to do. It will only require two things: water, and a cannabis plant in some type of growing system. 

When flushing it will depend on the type of system you are using, in the last one to two weeks before you harvest your cannabis you change the nutrients in the system (hydroponic cannabis growing systems) to plain water and use this water over the roots for the last weeks of growing. 

The idea behind this is to only feed the cannabis plant water so that it will force the minerals and plant nutrients that are still in the plants buds, and leaves to be used up before the grower harvests the plants.

When Should Growers Flush Cannabis?

Many growers have their own preferred time to start flushing cannabis plants. Some will start flushing 14 days before harvest while others will only do so for 3 to 7 days before they harvest the plants. This is really up to the grower and what has worked before for them and what they feel comfortable doing. We recommend not starting your flush before 14 days as the plant may not have enough minerals stored up to last till harvest in the plants causing issues with the plant’s health and growth. 

Another time to flush cannabis plants is if you are experiencing nutrient imbalance in the growing medium or lockout.  When this happens you can use plain water, and run it over the medium flushing anything in the growing medium out. We recommend doing this a few times to make sure everything is flushed from the medium so you are starting with a clean slate. You may even like to not use anymore nutrients on the plant for a couple of days to assess how the plant reacted to the flush and if the issue starts to correct itself.

When to Flush Cannabis Growing Hydroponically?

When growing using a hydroponic growing system it is recommended to flush your medium every nutrient change. This is because the nutrient salts from the fertilizers can build up in the system itself.  To prevent this from happening in this type of system, when you switch out old nutrient solutions for new ones it is recommended that you fill the system with plain water and run that through the system for a few hours. Then empty the plain water that was used for flushing and add new water and nutrients as required. We have a great article here you can read about growing Hydroponically.

Should Growers Flush Organic Soil Growing Plants?

Since you are not using any salts that can build up in the growing medium when growing organically, there really is no reason to flush either during the growing cycle or before harvesting the buds. The point of organic growing is to feed the soil as much as the plant. There shouldn’t be a build up of nutrients in the organic soil medium and therefore no reason to have to flush anything out of the plant before harvesting. Doing so when growing organic can upset the balance in the soil by removing foods for the bacteria that are living in the soil and helping the plants to thrive.

How to Check if you are Flushing Cannabis Correctly?

This is where you will require a PPM meter and PH meter, you can read more about these meters in our Hydroponic Cannabis Growers Guide here. 

Using these two meters you can check the runoff of the water that is being used to flush the growing mediums. After flushing whatever medium that you are working with, collect some of the water that runs out the bottom of the container or back into the nutrient reservoir. Take your meters and test the plain water first to use as a baseline for your runoff test. 

The water that comes out of the bottom of the container or in the reservoir should be close for PH and PPMs to the plain water you used for the baseline tests. If it is close to these levels then you have flushed your plants successfully. If you are still reading high levels of PPMs or PH ranges that are not correct then you should continue to flush with plain water until the runoff reaches this point.

PH and PPM Meters

Is Flushing Cannabis a Replacement for a Good Dry and Cure?

No, we still recommend that growers do a proper dry and cure of their cannabis plants, this process only works for removing excess minerals from the plant which will help the taste when smoking your buds but does not replace a good curing of the buds after harvest. You can read more about drying and curing your cannabis buds here.

Things that Growers will add to Water When Flushing Cannabis Plants

Some growers will like to add sugars to the plain water when flushing their plant before harvest. These are some of the things that growers like to use when flushing.

Flush Cannabis with Molasses

One thing that growers will add to their plants when flushing is molasses, they do this to add enzymes for the plant to use in the form of the sugars that are in molasses. Many growers will debate if this is needed when flushing. We have a great article you can read here about using molasses for growing cannabis plants.

Molasses Growing Cannabis Plants

Do Buds Grow During Flushing?

Yes, your buds will have stored up minerals and nutrients in the leaves, roots and buds of the plants. They will continue to use these up until the plant runs out of them. If this happens before harvesting then the plant will most likely show signs of deficiencies. This is why we don’t recommend starting a flush before harvest for more than 14 days.

The Debate about Flushing Cannabis, Is Flushing Necessary?

Flushing plants before harvest is a highly debated subject in more growing communities. Some growers state that it is just “bro science” and that it isn’t necessary to harvest great buds. They said it may even hear your harvest by removing needed minerals from the medium before the plant is ready to harvest. While others say that it is essential to having good smoking buds. 

We currently only grow organic using soil so there is never a need to flush out cannabis. However when we used to grow hydroponically years ago it was worth flushing between nutrient change as we seemed to have far less issues with salt build up in our systems.

Final Thoughts

We believe that if you try something and it works for you then to keep doing it if it works well for your growing style. If you flush and find that it is a good process for your style of cultivation then there is really no reason to change anything, and the same goes for not flushing, let us know in the comments if you are a flusher or a non-flusher and your reasons for doing so.

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