When and How to Flush Cannabis Plants

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It is crucial that cannabis growers know how and when to flush your plants if you want to be a successful cannabis cultivator. Knowing how to perform a proper flush will help your finished product taste better, smoke better and be a higher quality product.

I have grown for decades and have created a foolproof system for the 3 times that you should perform a flush and the 6 steps to ensure a successful flush.

Follow along in my step-by-step guide and I will teach you how to flush cannabis plants!

What is flushing cannabis plants?

Flushing is a technique used to rinse away excess nutrients and buildup in the root zone in the soil or growing medium. 

It is typically done by pouring large amounts of plain, pH-balanced water through the growing medium. In other words, when we say “flushing a plant”, we’re essentially talking about giving the plant a deep cleaning.

It’s like taking a shower after a long, sweaty day. Just as you feel refreshed and reinvigorated, so do your cannabis plants after a good flush.

Flushing is done on three occasions:

1. Two weeks before harvest — To remove any nutrient build-up that would make its way into the buds. A good pre-harvest flush starves the plant and helps bring out more of its natural flavors. Not flushing will make the flower taste poorly and the smoke will be dark and nasty.
2. To correct deficiencies or nutrient burn — If your growing medium has an imbalance, you can perform a flush so that you can re-administer a balanced cannabis nutrient mix.
3. To correct nutrient lockout — Similarly to when you have a deficiency, you can flush your plants to correct nutrient lock.

How to Flush Cannabis Correctly?

Flushing cannabis plants is simple so don’t fret. How you do the flush will depend on the size of your pots. The bigger the pot, the more work to flush.

If you have anything larger than a 1 gallon pot, or if you have more than 5 pots, I recommend that you pick up a few cheap tools that will help make the process easier but you can do it without any extra tools if you’re in a pinch.

The goal is to avoid overwatering the plants while thoroughly rinsing your growing medium multiple times until the water that is pouring through is clean and clear

Tools

• Garden hose
• Small water pump
• An automatic spray nozzle
• 5 gallon buckets (at least 2 buckets)

Step 1: Monitor Your Cannabis Plant’s Life Cycle

Flushing is typically done in the late flowering stage, about one to two weeks before you plan to harvest. Be sure to closely monitor your plant’s trichomes and pistils to accurately determine the right time to start the flushing process. Harvesting at the right time is important, so learn to read your plants to see when they are ready to pre-harvest flush (more here).

Step 2: Prepare Your Water

Get your water ready for the flush. The water you use should be pH balanced, ideally between 6.0 and 6.8. To ensure you’re not adding any unwanted elements into the mix, we recommend using Reverse Osmosis (RO) water for the best results but plain water from the tap works too (check the pH and water quality in your area).

Reverse Osmosis (RO) water is purified water that has had most of its dissolved salts, minerals, and other impurities removed. It’s the ideal water for flushing because it ensures you’re not introducing any new contaminants during the flushing process.

Step 3: The Flush

In soil

On your regular watering schedule, use the pH-balanced water from step 2 and heavily water your plants until water starts coming out from the bottom of the pot. Don’t stress the process, water slowly with a sprayer that covers the entirety of the soil.

Keep watering until you see the water running out from the bottom of the pot get clearer. It does not need to be completely clear because you run the risk of drowning your plant but aim for a clean and clear transparency.

If you have large pots or many pots, I recommend using the previously mentioned tools. Put the water pump in the pot saucer with the hose attached to pump water into a bucket. Attach the automatic sprayer nozzle to the bottom of the plant so the spray covers the surface of the soil. Keep the water running out of the pot at the same pace as the water pump.

If you only have one or a few smaller pots (around 1 gallon), you can flush by bringing your pot the the sink and just run water through the soil.

Coco or Hydroponics:

For these quick-draining systems, just replace your nutrient solution with the pH-balanced water and Amplify and let the system run as usual. Coco and hydroponic systems typically need 5-7 days to be adequately flushed.

Step 4: Monitor the Runoff

The runoff water can tell you a lot about how effective your flush is. Initially, it may be dark due to the nutrient salts being flushed out. The goal is to keep flushing until the runoff water is as clear as the water you’re feeding your plants without over watering

Step 5: Continue Regular Care

Even while flushing, your cannabis plants still need regular care. Continue with your standard light schedule and monitor your plants for any signs of stress or disease.

Step 6: Harvest

After flushing, it’s a waiting game. “How long to wait after flushing can you harvest?” you may ask. This usually depends on the readiness of your plant. Once you’ve seen that the majority of the pistils have darkened and receded, it’s usually safe to harvest. Flush until harvest, don’t go back to adding  nutrients. Let plants dry down some right before harvesting.

Why Flush?

The primary reason we flush is to improve the quality of our final product. Excessive nutrients can affect the taste and smoothness of your smoke. If you’ve ever had a harsh, chemically tasting bud, it’s likely it wasn’t flushed properly.

Another reason is to help correct nutrient lock. Nutrient lockout can occur when excess salts build up in the soil, preventing the plant from absorbing nutrients effectively. Flushing nutrients excess can help alleviate this issue, enabling the plant to intake the nutrients it needs for healthy growth.

Amplify (beneficial microorganisms) is a super helpful product to have in your arsenal, it helps prevent nutrient lockout and balances out the nutrients in the soil so that they are easier for your plants to take in.

The Best Time to Flush Your Cannabis

Knowing when to flush your cannabis is crucial. Timing depends on the type of cannabis you’re growing. If you’re asking “when to flush autoflower”, you’re in luck. Autoflowers typically need to be flushed about a week before harvest.

As for photoperiod strains, the flushing process should begin when most of the pistils have darkened and receded. This is typically 1-2 weeks before harvest, so if you’re wondering “is 1 week flush enough”, the answer depends on your plant’s readiness for harvest.

In terms of frequency, if you’re asking “how often to water during flush”, it’s typically the same as your regular watering schedule. The key here is not to overwater. That brings us to our next topic: “how to flush plants without overwatering”. Stick to the same/maybe just a bit heavier than the regulated water schedule. Flush like you are watering on a hot dry day

The Importance of Enzymes

Consider using a quality enzyme supplement during your flush to aid in breaking down nutrient salts that may be hard to flush out. A quality enzyme supplement can help make your flush more effective.

When to Avoid Flushing Your Plants

While flushing can be beneficial, there are times when it might do more harm than good. If your plant is already stressed due to overwatering, disease, or pests, flushing could exacerbate these issues. In these cases, a more gentle approach to nutrient management is often better.

Is Flushing Really Necessary?

This is a contentious issue among growers. While some swear by it, others see no noticeable difference. Our stance? While not always necessary, it can significantly improve your final product’s quality when done right. So for us, the benefits outweigh the extra effort.

Learn about cannabis nutrient deficiencies