Flushing Cannabis Plants: Everything you need to Know

Flushing Cannabis Plants: Everything you need to Know

Jan 3rd 2024

Flushing the cannabis plants before harvest can make an immense difference in the final product. It is an essential step in the cannabis cultivation journey that cannabis growers should not overlook. Flushing cannabis plants removes leftover minerals and nutrients buildup from the plant's roots and soil to give them a fresh start. It improves the quality of your buds and allows your plant to absorb nutrients that are still in the soil.

Every successful cannabis cultivator knows the benefits of flushing and the proper way to perform a flush that helps the finished product smoke better, taste better, and be an excellent quality product. However, timing is a crucial factor when it comes to flushing marijuana plants. So, growers should know when and how to flush cannabis effectively.

Whether you're a beginner or a seasoned grower, this guide will help you clear your doubts about flushing your plants and help you perform the process correctly for a high-quality harvest. Let's explore when, why, and how to flush your cannabis plants.

What is Flushing?

Flushing cannabis is a process of running plain water to remove excess nutrients and chemicals in the soil or any growing medium. It is done by passing large amounts of pH-balanced water through the soil and draining it away. Any nutrients and minerals in the soil will be washed away by the water, leaving the soil clean.

In simple words, when we say we're flushing a plant, we mean flooding it with water and giving it a deep cleaning.

You must be wondering why you should rinse away all the minerals from the growing medium, and if it will harm the harvest. When excess nutrients are removed, it allows your plants to use up the remaining nutrients, keep the plants healthy, enhance the harvest quality, and prevent many issues like nutrient burn.

What is the Best Time to Flush Cannabis

Here is when and why you need to flush your cannabis plants.

Flushing Before Harvest

Flushing starts two weeks or ten days before harvest. Pre-harvest flush helps enhance the quality and smoothness of cannabis plants. It forces plants to use the stored nutrients, remove excess chlorophyll, and prevent harshness.

If the plant has a flowering period of eight weeks, flushing should occur six weeks after the beginning of the flowering stage. If the flushing is done early, it'll highly affect the harvest. Examine the trichomes closely on your plant to determine when your cannabis plant will be ready for harvest. When tiny trichomes start to change from clear to milky color, it may be a sign that the plant is ready to flush.

Nutrient Lockout

Flushing is not limited to harvest time. This method is also used during the vegetative phase to remove excess nutrients from the growing medium. Although nutrients keep the plant healthy, too many nutrients can result in a problem called nutrient lockout. A nutrient lockout is a state where your plants are unable to access nutrients from the soil. This problem can be caused by improper pH levels and salt buildup. The best way to solve this problem is by flushing plants.

During nutrient lockout, the nutrients bond with the minerals, so plants can't absorb the nutrients. When the plants are flushed, the bonding is reversed, and then the nutrients can be absorbed.

Changes in the Nutrient Cycle

During the plant's life cycle, the soil undergoes different changes and requires different nutrients depending on the growth stage. Therefore, cleansing is a good way to prevent unfavorable soil changes and reset soil while a plant is entering a new growth stage. Flushing maintains the ideal state of soil and prevents various problems. When plants reach the flowering stage, flushing can benefit it by offering maximum nutrients.

Imbalanced pH

Another right time to flush the cannabis plants is when the soil pH is imbalanced. The presence of excess salts and nutrients causes an imbalance in pH. Improper pH damages the plant and causes nutrient lockout.

As a grower, you should test the pH of the soil regularly. When you notice the pH is not ideal, flush the plant. Flushing will help restore the pH to an optimal level.

Accidental Over-fertilization

Sometimes, growers over-fertilize the plant, which can harm the plants. In the case of over-fertilization, you can reverse it by flushing the plants. Flushing your plants removes the excess fertilizer or nutrients. As a result, it restores the soil's favorable condition.

How to Flush Cannabis Plants Properly

Flushing cannabis plants is a relatively straightforward process. Instead of feeding the plants, you flush. If you are flushing plants before harvest, use untreated tap water. If there's an issue of improper pH or nutrient unlock, it is recommended to use pH-balanced water. Most tap water has an optimal pH level and doesn't require treatment. pH adjustments are the crucial thing that significantly matters in this process.

Step 1: Use a pH meter to test the pH level of water. Ensure the water is in the favorable pH range for cannabis plants, which is between 6.0 and 6.8 for soil grown.

Step 2: Flood the soil with fresh water. Pour water slowly and as much as the soil can hold. Wait for a few minutes to allow nutrients to be fully absorbed.

Step 3: Pour the water into the soil again to flush out all these nutrients. If you're using pots, you will observe the initial water draining from the bottom, which will look dirty and stained. After flushing, the color will lighten and appear cleaner.

Step 4: Use a TDS (total dissolved solids) reader to measure the TDS of the drained water and determine its purity. The ideal reading is below 50 ppm. Keep flushing the plant until it is close to the TDS of fresh water you are flushing with.

Step 5: Once you're done flushing the plant, let it dry and take it back to the growing area. The plant might take one day or more to dry. So, let it dry completely and avoid watering the plant during this period.

When to Avoid Flushing

Flushing is highly beneficial to plants, but there are times when it should be avoided because it might do more harm than good. Avoid flushing when you are growing cannabis in amended organic soil. This growing medium has been carefully developed over time and is home to beneficial microorganisms. Flushing can wash away this delicate biodiversity.

Furthermore, you should avoid flushing when your plants are already stressed due to overwatering, pests, and diseases because flushing may exacerbate these problems.


Flushing cannabis plants is an important part of the marijuana cultivation process. It can make all the difference in the quality of your harvest. Cannabis flushing is proven to produce a cleaner and smoother smoke with better taste and improved potency. By understanding the process of cannabis plants and the right timing, growers can minimize problems like nutrient lockout and nutrient burn and lead to higher-quality harvests. So, flush your cannabis plants, improve their health, and enhance the quality of your harvest!

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