Why and How to Flush Your Cannabis Plants

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Flushing is probably one of the things newbies tend to overlook. It is as simple as it sounds: you flush out unwanted nutrients from your growing medium so that overfed plants can recover, nutrient absorption can be improved, and nutrients can be drained from buds that are about to be harvested. New growers tend to focus and even obsess over what kind of nutrients to give their plants and when, but often fail to grasp the consequences of nutrient imbalance and overfeeding. Although this is somewhat understandable since it takes experience to recognize a nutrient problem and knowing when to do a flush, this is something that even first time growers should do prior research on.

If you have already invested in top-shelf strains, then you need to learn how to do a proper flush since it makes a tremendous impact on the taste, smell and overall smokability of the buds. To begin, let’s learn what happens to your soil and plant as you add nutrients to give you a better idea why you need to flush.

Why should you flush your marijuana plants?

Beginners often go for pre-mixed nutrient solutions since it is the most convenient: there’s little guesswork involved and you just follow the instructions on the bottle. Typically these bottled nutes will be formulated for different growth stages and will have varying levels of main macronutrients like nitrogen, phosphorous, and potassium, secondary macronutrients like calcium, magnesium, and sulfur, and micronutrients like zinc, manganese, iron, boron, chloride, cobalt, molybdenum, and silicon. 

Nutrient lockout and overfeeding

Your plants will use up these nutrients as they need, so you can expect some to be left over after some time. Often, the ones that will be left over are minerals and salts and once these build up in the soil, they can cause a “nutrient lockout” that will prevent your plant from absorbing the nutrients that it needs.

In some cases, the problem is that you’ve just fed your plants too much. You’ll probably realize that this is the case when you see signs of “nutrient burn” where the tip of the leaves of your plant curl up and turn yellow to brown. Not only this, overfeeding can also damage the roots, making it a serious problem that your plant may not recover from.

In both cases, a proper flush can “reset” your plant’s soil by dissolving and draining all the unwanted nutes. However, flushing alone won’t turn your overfed plants back to normal, which is why it’s important to do it at the right time.

Flushing before the harvest

Even if you’re not dealing with nutrient lockout or overfeeding, it is still good practice to do a flush before harvesting, especially if you used nutrients on your plants. What you want is for your plants to use up all the nutrients so that the taste and smell of your buds won’t get tainted. Otherwise, you could end up with harsh buds that won’t burn easily, even if they happen to be award-winning strains.

The only time you can skip flushing is if you already know how to balance your nutrients correctly, or if you’re using amended soil. Super soils usually contain a balance of organic nutrients and beneficial microorganisms that will get washed away with flushing.  

How do I flush my marijuana plants? 

Typically, flushing only involves using clean water with pH levels of around 6.5 to 7 but there are also flushing agents like Botanicare Clearex that address specific issues like salt buildup, although there are growers who would argue that water works just as well, but make sure that you are using pH neutral water with as little dissolved minerals and chemical treatment as possible. 

The idea behind flushing is simple: just use water to wash away the unwanted nutrients in your growing medium and don’t add any more fertilizer during the flushing period. Flushing soil usually takes 1 to 2 weeks, coco coir less than a week, and hydroponic just 2-3 days, but this really depends on the state of your soil and plants. If you want to make doubly sure that all of the lingering starches, carbs and whatnot are broken down, you can also use an enzyme-rich flushing formula like Hygrozyme.

When to do a flush

Flushing is all about timing rather than technique. While it doesn’t involve anything complicated, you just need to water your plants as normal, it is critical to know the right time to flush. You typically only want to do a flush during the growing phase if you’re certain that you’re dealing with a nutrient lockout or overfeeding problem, judging by the appearance of your plants. Otherwise, you should only do a flush right before you harvest when 50% or more of the trichomes have already turned milky white.

Frequently Asked Questions on Marijuana Flushing

How do I flush my marijuana plants?

You can use clean, minimally treated water with pH levels of 6.5 to 7 to flush out salts and excess nutrients from your growing medium. Flushing typically takes 1 to 2 weeks for soil and a week to a few days for coco coir and similar mediums, but the duration largely depends on the state of your plants.

Flushing before the harvest usually takes around 2 weeks right before the harvest, after the trichomes have turned milky white.

Why should I flush my cannabis plants?

There are a lot of growers that recommend flushing right before the harvest as it is believed to improve the smell, taste, and throat feel of the buds. Flushing can also be done during the vegetative state to reset the soil and address overfeeding issues, salt buildup or incorrect pH levels.


Even though flushing sounds like something every grower should be doing, some still think it is unnecessary. After all, it will cause the plant some stress. It is also quite tricky to figure out since every grow is different. One good rule of thumb that beginners may want to follow is that if your plant looks normal; doesn’t have a deep green color or yellowing of leaves, then you probably don’t need to do a flush. However, if you did use fertilizers or nutrient formulas on it, then you might want to do a flush right before harvesting.

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