Flushing Cannabis: A vital part of growing

Flushing Cannabis: A vital part of growing

Even if you are entirely new to cultivating Cannabis, I bet you have heard about flushing - stopping feeding your plants with nutrients and washing their root zone with plain water. In this article, I will go through why it is important and how to do it properly.


The main objective of flushing is to increase the final quality of buds by removing the remnants of the nutrients that tend to stick in the root system and soil. Flushing naturally helps the plant to get rid of the chemicals that affect the taste. As result, weed tastes better smells stronger, and smokes smoother.

Moreover, flushing before harvest can help in the face of nutrient imbalance. It will treat underlying causes of nutrient issues such as lockout or pH issues and help you get your grow back on track in less than a week.


There are 3 main techniques that experienced growers use, as you get more practise, it will be a great idea to experiment with every single one of them and see how it affects your plant. I wouldn’t say that one of them is the best, it really depends on individual tastes, set of nutrients and the strain.

  • When a plant switches to the blooming stage.

  • The Cannabis cycle has two main stages, the vegetative phase and the blooming phase. During these distinctive stages, plants require different nutrients. During veg, plants need higher concentrations of nitrogen (N) to boost the growth of healthy new leaves and promote photosynthesis. During bloom, cannabis plants stop growing their stems and foliage. Instead, they focus all of their energy on developing large flowers in hope of reproducing. In turn, flowering cannabis plants need higher concentrations of phosphorous (P) and potassium (K), which help encourage healthy plant structure and, more importantly, contribute to the production of large buds with strong aromas and flavors. 

    Some growers prefer to lightly flush their plants when switching from veg to bloom. While it isn’t considered to be necessary, it can certainly help to make a smooth transition from veg to bloom fertilizers. Moreover, it can also help eliminate the risk of chemical interactions between different fertilisers, which can cause salt buildup and nutrient lockout.

  • To treat nutrient lockout

  • Nutrient lockout is a rather common problem that occasionally arises even for veteran growers. Most often it is caused by salt build-ups in soil, which get generated by chemical reactions between the root system, its growing medium and your fertilizer. Plants under nutrient lockout essentially are not able to take up nutrients which leads to such symptoms as stunted growth and limp leaves with burnt tips.

    When you diagnosed a nutrient lockout in your plants, flushing will help you to correct it quickly. It is important that the pH of the water is as friendly to Cannabis is possible. The ideal pH for weed is between 5.8 and 6.2

  • Pre-harvest flushing

  • By far the most popular period to flush Cannabis is right before the harvest. Whilst it isn’t scientifically proven that such a method truly improves the taste and effects of smoking, many growers remain adamant claiming that it significantly improves the quality of the final product.

    In terms of the timing, individual approaches vary, but typically growers flush their plants 1-2 weeks before the harvest. From my point of view, flushing isn’t necessary if you haven’t been using fertilizers extremely heavily during the blooming stage, or if you only used organic nutrients during the entire grow. 


    As we have discussed, flushing is a simple process of drenching a plant’s medium with pH-regulated water. However, how do you know how much water is needed and when to start giving nutrients after flushing?

    The amount of water is determined relatively simply. In order to effectively flush your plants, you need more water than you use for general watering. Ideally, you would want to water as much to produce 10-20% of water run-off from the bottom of the pot. In order to do so, simply divide the size of your pot by half. E.g. if you grow in 15l pot you would need 7.5l for decent flushing.

    Note that it is quite an excessive amount, therefore a plant will not need more watering for the next 5–7 days. It is optimal to do the flushing 7-10 days before you plan to harvest. When flushing to prevent nutrient lockout wait a minimum of 7 days before starting using fertilizers again.

    Hopefully, that helps! I will be glad if you will share your experiences with flushing in the comment section below.

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