Phosphorus Excess in Cannabis Plants

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Phosphorus excess in cannabis plants is a rare plant problem to have. This is because phosphorus is a macronutrient, which means cannabis plants use a lot of it. But even though plants use a lot of phosphorus, there may be times when they get too much of it.

In this guide, we cover everything you need to know about phosphorus excess in cannabis plants. This includes, what it looks like, how it happens, and what you can do to fix it.

To begin, we will explain how cannabis plants use phosphorus. This will give you an idea of how much your plants need, and when they may need it. Feel free to skip to any section of this guide by clicking on the menu.

How Do Cannabis Plants Use Phosphorus

Cannabis plants use phosphorus in many ways. It helps buds grow big, and plays a big part in root formation too. It helps seeds germinate, and it will help clones make new roots. 

Phosphorus is also a major element used in photosynthesis. A large amount of the light your plant absorbs will be stored as phosphorus. Because it is also a mobile nutrient it can move to different places in the plant where it is needed. 

Because a lot of phosphorus is used by cannabis, it is not very often you will see an excess. You are far more likely to see a nitrogen, or potassium excess first. So keep an eye out for those symptoms.  

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Symptoms of Too Much Phosphorus in Cannabis Plants

If cannabis plants get too much phosphorus, the plant will stop absorbing micronutrients and trace elements such as, calcium, magnesium, zinc, and iron. You are likely to see the symptoms of other deficiencies before you see signs of phosphorus excess.


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  • Yellow veins on top leaves
  • Leaf tips will be burned
  • Micronutrient lock out
  • Thin blades on new leaves
  • Lower leaves curl
  • Spots on lower leaves

The best way to fix a potassium excess in cannabis plants will differ depending on what medium you are growing in. But before we go onto that, we should cover how your plant get phosphorus excess in the first place

How Cannabis Plants Get Phosphorus Excess

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Phosphorus is absorbed into the plant via the roots. The microbes in the medium, and the roots of the plant work together in a symbiotic relationship. The microbes help the plant absorb more phosphorus, and in return the plants give the microbes starches and sugars. 

To have too much phosphorus in a cannabis plant, you would usually be overfeeding the plant with a PK booster.

In most cases it is simply down to the grower feeding the plant too much phosphorus. So the problem is easily solved. 

How to Fix Phosphorus Excess in Cannabis Plants

To fix a phosphorus toxicity in cannabis plants, the best thing to do is remove some of the phosphorus from the medium. Doing this will reduce the amount available to the plant, so it cant have so much. The way you do this will depend on whether you’re growing in soil, coco, or hydro.

Fix Phosphorus Excess in Soil and Coco

When a cannabis plant has phosphorus excess, it means there is also a lot of phosphorus in the medium. To solve this, you need to remove some phosphorus from the medium. 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 phosphorus, you will not need a big flush. Just follow these steps here:


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 Phosphorus Excess in Cannabis Plants Grown in Hydro

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


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 phosphorus excess or anything else, just ask for help in our forum for cannabis growers.

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

How to Prevent Phosphorus Toxicity

Cannabis plants absorb phosphurs 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 phosphorus in the medium, there will not be in the plant either. 

To Summarize:

If you have phosphorus excess on 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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