Potassium Excess in Cannabis Plants

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Potassium Excess in cannabis plants is not seen often. Just like phosphorus and nitrogen, potassium is a macronutrient, meaning plants use a lot of it. You would have to over feed a plant a lot for it to get potassium toxicity. In which case other excess problems would show first. 

In this guide, we explain everything you need to know about potassium excess in cannabis plants. From what it looks like, how it happens, and what you can do to fix it.

First off, we will explain how cannabis plants use potassium, and how much of it is used at different stages of growth. Feel free to skip to any section of this guide by clicking on the menu.

How Do Cannabis Plants Use Potassium

Potassium is used to move things like water, nutrients and sugars around the plant. It also regulates the opening and closing of the pores (stomata) on the plant’s leaves. 

Essentially, potassium helps the plant eat, and breathe. Plants use a lot of it, and the only element they use more than potassium is nitrogen. Whilst nitrogen is used to essentially build the plant, potassium is what the plant uses to move things around.  

Water is moved around the plant with the potassium. It is absorbed through the roots, and evaporated away through the pores in the leaves as the plant breathes. This is all down to potassium. It is a vital element in plant growth.

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Symptoms of Too Much Potassium in Cannabis Plants

Because plants use potassium in such high levels, it is not common to see a potassium excess. Instead, the plant will absorb as much potassium as possible. As a result, other elements like calcium, magnesium and zinc are left behind.


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  • Top leaves have thin blades
  • Leaf tips and edge develop burn
  • Micronutrient lock out
  • Bottom leaves have brown spots
  • Lower leaves curl
  • Acidic root zone

If you see symptoms of cal/mag or any other trace element deficiencies in cannabis plants, it may be down to over feeding them. Potassium and phosphorus toxicity will stop plants from absorbing the micronutrients they need.

How Cannabis Plants Get Phosphorus Excess

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It is very hard to over feed cannabis plants potassium if you’re using the right nutrients. The nutrients made for growing cannabis plants will have the right NPK ratio. If you’re using “grow nuits” during veg and “bloom nuits” during flowers, you shouldn’t have this problem. 

In most cases, a potassium excess will come during the flowering stage, when a PK booster is added to the feed.

Sometimes potassium excess may show in young plants in strong soils. So use a potting mix for seedlings and young plants.

How to Fix Potassium Excess in Cannabis Plants

To fix a potassium toxicity in cannabis plants, you should remove some of the potassium from the medium. This will reduce the amount of potassium available to the plant. The method you use to do this will differ depending on the medium you are growing in.

Fix Potassium Excess in Soil and Coco

When a cannabis plant has potassium excess, it means there is too much of it in the medium. To solve this, you need to remove some. This is can be done by “flushing”. 

How to Flush Soil and Coco. 

To flush soil and coco, all you have to do is pour water through it. This will wash out some of the excess nutrients and will restore some balance to the medium. To remove excess potassium, you will not need a big flush. Just follow these steps here:

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Start off with a bucket of water that has the same amount of water in it, as your plant pot has soil/coco. For example, 20l of water, for 20l of medium. pH that water to around 6.2-6.5 for soil grows, and 5.8- 6.2 for coco grows.


When the pH level of the water is correct, pour the water into the medium. It will wash through and pick up salts it washes past. The water then leaves the medium through the bottom of the pot. That is your run off.


Collect the run off to make sure your plant is not sitting in it. Reduce the amount you have been feeding the plants by at least 10%. In coco grows, feed straight after the flush. But only water soil grows for a few feeds.


Fix Potassium Excess in Cannabis Plants Grown in Hydro

To fix a potassium excess in cannabis plants grown in hydro, you need to reduce the amount of potassium available in the reservoir. You can do this by either diluting the solution that is in your reservoir, or completely changing it to a new feed. 

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Begin by checking the EC/PPM of the nutrient solution in the reservoir. Take note of the levels, you do not want it to be this high again after you have changed the reservoir. Try reducing this amount by 25%. 


Dilute the reservoir with water that has no nutrients in it at all. Balance the pH of this water between 5.8 and 6.2 before adding it to the reservoir. These levels are preferred by plants growing in hydroponics. 


Bring the EC/ PPM of the reservoir down by around 25%. From here you can watch the plant for a few days to see if it makes any changes. As soon as the plant starts to look hungry again, increase the EC a little. 


Has this Guide Helped You?

I hope this guide has been useful to you, and it answered all your questions. But if you still need more information on potassium excess or anything else, just ask for help in our international cannabis forums.

Please consider helping us by joining our community, sharing this post, or even becoming a Patreon!

How to Prevent Potassium Toxicity

Cannabis plants absorb potassium through their roots. So the best way to prevent any kind of nutrient excess or toxicity issue, is to not feed too much!

It is much easier to fix an under fed plant than it is to fix an over fed one. Don’t forget that. So keep the feed light, increase it gradually, and try not to overfeed your plant. If there isn’t excess level of potassium in the medium, there will not be one in the plant either. 

To Summarize:

If you have potassium excess in your cannabis plants, it is most likely down to you over feeding them. Reduce the amount of nutrients available to your plant by flushing the medium, or changing the reservoir. 

Then reduce the amount you feed your plants in the future too. Over feeding is easy to do, so don’t be too hard on yourself about things like this. Take it as a lesson, fix the problem, and continue growing your beauties! 

If you need any help, you know where to find us! 

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