Everything you need to know about growing cannabis at home

Potassium Problems and Cures for Cannabis Plants

by | Aug 15, 2022 | Cannabis, Getting Started, Nutrients, Troubleshooting

Potassium is an essential nutrient for your cannabis plant, but one that many growers neglect. Inadequate potassium can lead to potassium deficiency in cannabis plants and potassium toxicity too. If you want to avoid these problems, make sure you are getting enough potassium from the right sources. That’s where this guide comes in!

What is potassium?

Potassium is one of the elements that your cannabis plant needs to grow. It is found in trace amounts throughout the entire plant, but potassium’s main job is helping your roots do their work among other benefits we will detail below. Adequate potassium nutrition prevents nutrient deficiencies and helps improve yields.

Potassium can be found in different nutrients for your plants including many of the potassium-rich nutrients that are available at many garden centers. Potassium is the third number on most nutrient bags, which are the numbers representing nitrogen or “N”, phosphorus for “P”, and “K” for potassium. For example, a bag may be labeled “1-9-4” which means it contains 1% nitrogen, 9% phosphorus, and 4% potassium by weight. The remaining percentage of the bag or liquid is simply the carrier material for these nutrients.

Why do cannabis plants need potassium?

Potassium is an essential element for your cannabis plants. It is the potassium that helps transport water and nutrients to different parts of the plant, as well as help regulate photosynthesis. A potassium deficiency in cannabis plants will result in yellowing leaves, stunted growth, and wilting foliage. Adequate potassium in the soil prevents nutrient deficiencies that can cause problems like interveinal chlorosis, which is the yellowing of leaves between leaf veins. Potassium is also key in preventing stem elongation which helps increase yields when compared to stems that are long and weak. Cannabis plants need potassium in both the flowering stage and vegetative stage.

Is potassium a macronutrient or micronutrient?

Macronutrients are the nutrients that your cannabis plant needs in large amounts for growth. This includes potassium, nitrogen, and phosphorus as some of the main macronutrients. Micronutrients are nutrients that your cannabis plant needs only in small amounts, which include iron and zinc as some of the main micronutrients. Potassium is a macronutrient just like nitrogen and phosphorus, the other two macronutrients that are included in the labeling of nutrients.

Is potassium a mobile or immobile nutrient?

Mobile nutrients are nutrients that can be transported throughout your cannabis plant, allowing for deficiencies to appear in different parts of the plant. Immobile nutrients are not able to be transported throughout the plant. Since potassium is mobile it can be absorbed by different parts of your cannabis plant, allowing for potassium deficiencies to show up between the veins on leaves or in different parts of the root system.

What does potassium deficiency in cannabis plants look like?

A lack of potassium, also called a potassium deficiency, in your cannabis plant will first become noticeable with yellowing and browning between the veins of lower leaves, also called interveinal chlorosis. As it progresses, these symptoms spread to bigger fan leaves until eventually, they appear throughout the plant.

Other common symptoms include the margins and tips of the leaves of potassium deficient cannabis plants will also suffer from rust-colored or brown spots appearing to look like a light or nutrient burn. Stunting in growth begins when potassium deficiency starts to affect the lower parts of your cannabis plant. The ends of fan leaves begin browning and die, while older leaves become yellowed, which means they are suffering from chlorosis, like the smaller leaves. When potassium deficiency is severe, parts of the plant begin to “stretch” as older leaves stop growing but new ones do not replace them. The stems of your plant may become weak and your yield will be diminished too.

How do you fix a potassium deficiency?

A potassium deficiency in your cannabis plant is easily fixed by adding a potassium-containing nutrient to the soil, as well as making sure that you are watering your plant correctly. A cannabis potassium deficiency can also often be linked with calcium and magnesium deficiencies. Calcium and magnesium deficiencies will show up in the same symptoms as potassium deficiency, so it is best to look for both key nutrient deficiencies at the same time and make sure your plant is getting the proper nutrients and amounts of potassium it needs. Natural alternatives that contain potassium are wood ash, cocoa shells, chicken manure, and organic seaweed

How do you prevent a potassium deficiency?

Using soil that has adequate levels of potassium already included will help prevent potassium deficiencies from appearing. Some cannabis growers use a potassium-heavy nutrient regimen to make sure potassium levels are high enough throughout the whole plant, not just in one area or another where it might show symptoms of deficiency.

What does potassium toxicity look like in cannabis plants?

Potassium toxicity is much more common than other toxicities and can appear in potassium-overdosed cannabis plants. Unlike potassium deficiency, potassium toxicity will start with the lower leaves developing spots and curling of the leaves. It may also develop leaf tip burns and will often look similar to calcium or magnesium deficiencies.

How do you fix potassium toxicity?

There are no easy fixes for potassium toxicity that can easily be applied topically or even through soil amendment. Just like most problems with excess nutrients, you will need to flush your potassium-overdosed cannabis plants with clean, pH’ed water in order to get rid of excess potassium and bring down the levels back in line with what is healthy for your plant.

How do you prevent potassium toxicity?

Preventing potassium toxicity in cannabis plants can be difficult due to how easily potassium moves throughout the plant. If you are adding potassium-heavy nutrients to your cannabis plants, make sure that they aren’t getting more potassium than what they can use, and try using potassium supplements in moderation. If uncertain, you can always use half or a quarter of the recommended dosage and work your way up to the recommended dose of the feeding schedule if necessary.


Potassium is a mobile, macronutrient that your cannabis plant needs to survive. It helps the plant with photosynthesis and supports its root system and healthy growth. If your plant suffers from a potassium deficiency, there may be some chlorosis and brown or copper spots that will look like burn on the leaf tips or leaf margins.

To fix signs of potassium deficiency, simply add potassium-rich nutrients to your soil or medium. Preventing potassium deficiencies can be done by providing the right nutrients for your growing medium and supplementing as necessary. Potassium toxicity is one of the more common toxicities that can be found in cannabis plants. If your plant is suffering from potassium toxicity, the lower leaves will develop spots, brown, and curl up. It can look similar to calcium or magnesium deficiencies too.

To fix potassium toxicity you will need to flush your plant with PH’ed water to ensure it can start with the absorption of potassium again. Preventing potassium toxicity requires you to only use the required amount of nutrients with potassium. You can always use a quarter or half of the prescribed dose if you are uncertain about how much and then gradually add more if it is needed.

Thank you for reading our article, if you have any further questions please see our articles regarding PH’ing your water, flushing your plant, calcium deficiency, magnesium deficiency, light burn, and nutrient burn.

To learn more about growing cannabis at home consider checking out our guides on: Getting Started, Troubleshooting, and Optimizing your Grow or search our Knowledge Base.

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