What is Potassium Deficiency? And How Do You Fix It?

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Added 11 April 2022

Have you noticed any weird changes in your cannabis plant, such as the leaves losing their color, the plant growing tall but weak, or leaves turning brown and falling off?

These unnatural changes are likely due to potassium deficiency — one of the most common problems cannabis growers face, especially in the flowering stage. Potassium is one of the three principal macronutrients cannabis requires, but its deficiency is often subtle and hard to notice until the canopy starts suffering. 

However, you must not confuse potassium deficiency with other problems like a light burn, stress, or other deficiencies with similar symptoms. 

In this article, learn what potassium deficiency is, how you identify it, and different ways of fixing it.

Role of Potassium in Cannabis Plants


Potassium (K) is one of the most crucial macronutrients cannabis plants require, the other two being nitrogen and phosphorus. And it plays quite a vital role in maintaining the plant's structural integrity via turgor pressure, which helps the cells keep the plant in shape and prevent wilting.

Potassium also helps the plant breathe via the stomata — special cells on the leaves' underside — which open and close to exchange gasses and vapors. Lack of adequate potassium can hamper stomata's functioning, decreasing the plant's photosynthesis ability.

That's not all! Potassium helps your cannabis plant in various other ways, such as the following:

  • It assists the plant in excreting waste compounds by activating the biochemical enzymes.
  • It builds cellulose to reduce lodging in the plant.
  • Aids the movement of nutrients, carbohydrates, and water within the plant.
  • Helps with the production of ATP, protein, and starch.
  • Improves the plant's resistance to diseases and cold by managing respiration and temperature regulation.
  • Promotes root development and its drought resistance.
  • Helps fight various diseases by building immunity.

So, potassium is quite essential for the plant's health and well-being.

Causes of Potassium Deficiency

deficiency of potassium in cannabis

Despite being super important for the plant, many growers often face potassium deficiency in their plants. Unfortunately, this deficiency is quite common. Here are some of the most probable causes of potassium deficiency in your plant.

Lack of Potassium in the Grow Medium

The most obvious cause of potassium deficiency occurs when there's a lack of it in the soil medium. This is especially true for hydroponic systems as they lack natural potassium content, unlike soil. 

However, if you are sure the nutrient solution and grow medium contain appropriate potassium levels, you can check for other causes.


Cannabis is a resilient plant, but it can hamper its potassium processing capabilities if you stress it too much. So, stress caused due to over-pruning, incorrect transplant, high temperatures, etc., can cause potassium deficiency. 

pH Imbalance in the Root Zone

Many cannabis growers fail to realize the role of correct pH on nutrient availability for their plants. An incorrect pH level in the root zone can significantly affect the roots' ability to absorb nutrients, leading to various deficiencies like potassium deficiency. 

Excess Salts, Calcium, or Magnesium in the Medium

On the other hand, if your grow medium contains excessive salts, calcium, or magnesium, your plant may face potassium deficiency since it inhibits the root's ability to absorb potassium properly.

This problem is more common in soil or coco grow mediums compared to hydroponic systems since the grower can finely control the latter's nutrient presence.

Extreme Temperatures or Light Burns

Light burns or high temperatures can heat your plant, causing potassium deficiency. 

Symptoms of Potassium Deficiency

potassium deficiency in cannabis plants

At first glance, you may confuse potassium deficiency for other deficiencies or signs of stress. The symptoms often overlap. The most common signs of potassium deficiencies are as follows.

Lower and Middle Tiers

In the lower and middle tiers of the plant, you will notice various signs of potassium deficiency, such as the following:

  • The leaves may start turning yellow at the tip, which will then slowly advance towards the base of the leaves.
  • The edges of the leaves may appear burnt since potassium regulates temperature. Do not confuse this symptom of nutrient burn where the entire leaf seems to be burnt.
  • If the burning and discoloration advance, the leaves may lose color further, show spots of dead tissue, wrinkle, and eventually fall off.
  • The stem in the lower and middle tiers may also turn red, gray, or brown.

Upper Tiers of the Plant

Since potassium is a mobile nutrient, you may not initially see signs of deficiency at the top tier. Mobile nutrients are those that travel from one part of the plant to another. So, if there's a deficiency at the top with the young leaves suffering, the bottom or older leaves will send nutrients to the top. Therefore, a potassium deficiency is likely to begin at the bottom. However, you may see some signs at the top. Common signs of deficiency include the following:

  • You may see similar discoloration and burning signs in the upper tiers.
  • The plant experiences stunted growth. 
  • On the other hand, the plant may even experience stretching, where the plant grows tall but appears weak with smaller leaves and buds.


Potassium is essential for healthy bud development. So, a lack of it can significantly affect your buds. The common signs of deficiency on the buds are:

  • The buds may form later than expected. 
  • The buds may not grow as big and bushy as you would expect.
  • The buds may appear skinny.

This is a primary reason why most bloom-specific fertilizers are loaded with potassium.

Other Symptoms


You may even notice some other symptoms, such as the following:

  • Crispy leaf edges accompany the burn.
  • The fan leaves may turn entirely yellow while the veins remain green.
  • Leaves fall off prematurely.

Differentiating the Deficiencies 

As mentioned above, potassium deficiency can be similar to other deficiencies or stress. To differentiate the deficiencies well, you must understand what these other deficiencies look like.

Common Symptoms of Nitrogen Deficiency

  • The canopy will turn pale green.
  • Older leaves will turn yellow due to cell chlorosis.
  • The new growth of branches and leaves may be spindly and weak.
  • The plant may become more prone to mold, pests, or other diseases.

Phosphorus Deficiency

  • The leaves may turn yellow or blue-green, accompanied by scorched leaf edges.
  • The plant may shed leaves due to necrosis.
  • The leaves may develop brown or blue blotches.
  • The leaves may even curl up or become thick or stiff.

Light Burn

High-powered light panels, like LED and HPS lights, can lead to light burn, which has symptoms quite similar to potassium deficiency. And they are:

  • The upper tier of the plant may lose its color first as it is closer to the light panel.
  • The buds may bleach.
  • The leaves may curl up, appearing like tacos.
  • The plant may experience irregular growth.

A few other problems look like potassium deficiency, but the symptoms listed above are most apparent. 

Solutions to Potassium Deficiency

potassium deficiency marijuana

Since potassium deficiency causes vary, so do the solutions. Thus, the first thing you must do is figure out what is causing the deficiency and fix that issue at the root. 

Here are some ways you can address potassium deficiency in your cannabis plant.

1. Eliminate the Stressors 

The first step in addressing potassium deficiency is to eliminate other causes of stress for your plant that may be causing similar signs. This will further help you distinguish this deficiency from other problems.

Compare the symptoms of potassium deficiency with other problems using our cannabis problem-solving guides. Also, check whether it's heat stress or another deficiency

Then, check your light panels. High-wattage lights, especially HPS or HID lights, are notorious for causing light burns in plants. So, ensure you have placed your light panels at the proper distance from the canopy.

Ideally, LED panels must usually be at least 12 inches away from vegetative plants and 18 inches away from blooming plants, and HPS or HID lights must be placed even further. 

Or, better yet, follow the manufacturer's instructions and go through the light's user manual to know the right recommended distance and discuss with other growers to fix this issue.

You should also check the soil quality if you are growing in soil. Always use high-quality soil that is rich in potassium. If the soil is of low grade or lacks potassium, source some soil from a reputable vendor and transplant your plant. 

If such solutions don't fix your problem, you can be confident your plant suffers from potassium deficiency and not any other stressors. In that case, follow these tricks.

2. Check and Rebalance the pH in the Grow Medium

Soil pH

The right pH balance is crucial for a healthy plant. If the growing medium is too acidic or basic, it can hinder the root's ability to absorb nutrients properly, leading to various deficiencies. 

You can check the pH of the growing medium using a pH meter. First, measure the nutrient solution's pH. Then, measure the pH of the runoff drainage, and compare the two. This will give you an accurate measure of the growing medium's pH.

The pH for soil-based plants must be between 6.0 and 7.0.

Hydroponics ph

The pH for hydroponic plants must be between 5.5 and 6.5.

If the measurement is off, you need to rebalance the grow medium by flushing it. Follow these steps to flush your grow medium:

  1. Flush your grow medium with pH-neutral clean water. Use at least twice or thrice the size of the pot. For instance, if you're growing in a 10-gallon pot, flush it with 20 gallons to remove impurities. 
  2. Avoid giving nutrients to your plant for a few days, allowing the water to completely wash off the residual nutrients and salts.
  3. Then, rebalance the nutrient solution and feed it to the plant.

This should fix the pH issue for your plant, and the roots should be able to absorb potassium more freely henceforth.

3. Use Bloom Boosters

Bloom boosters are fertilizers explicitly formulated for flowering cannabis plants as they require more potassium and phosphorus for healthy bud development. So, using these fertilizers can give your plant a much-needed potassium boost. 

Plus, this is quite an easy and safe way to correct the problem. Most of these boosters are safe for flowering plants and are affordable to buy at your local nursery or gardening supply store. 

Cannabis, like any other plant, requires more or less the same nutrients, so you can use general bloom boosters if you find it challenging to find cannabis-specific boosters. 

However, before you choose the booster, you need to look out for some features, such as the following:

  • The booster must be rich in potassium and phosphorus.
  • The booster must have more potassium and phosphorus than nitrogen.

Additionally, you can choose between organic and chemical boosters. The organic ones are pretty beneficial for the soil but are slow to absorb. On the other hand, chemical boosters go directly to the roots, act quickly, and are more precise. 

Your goal must be to choose something safe for the plant and environment. But if you go with a chemical booster, ensure they are suitable for edible plants.

Regardless of the booster you use, read the ingredients label to check for compounds that may harm your cannabis plant. It's best to discuss with your local growers' community to explore your options. Or, ask questions here on Growdiaries. 

If you're in a hurry and need answers immediately, here are a few boosters meant for this purpose:

  • Botanicare Hydroplex Bloom (PK booster)
  • Humboldt Nutrients Ginormous (PK booster)
  • Canna PK 13/14 (PK booster)
  • Seaweed Bliss Premium Seaweed (K booster)
  • Humboldt Deuce Deuce (K booster)

To use them, follow the instructions on the packaging, but start with a slightly lower amount. Do a patch test first to ensure the compound does not harm your plant, and then work your way up to the correct quantity.

4. Make Homemade Banana Peel Tea


Banana is rich in potassium, so why not use it to give your plants a potassium boost? But this is not as simple as chucking a banana in your grow medium. Instead, you need to prepare a banana peel tea.

This tea will give your plant a potassium boost and help fatten the buds during bloom. 

Follow these steps to make your banana peel tea:

  1. Pour some water into a container. Let it sit for 24 hours if you're using tap water. If you're using filtered water, you can use it right away.  
  2. Place some pieces of banana peels in a jar, up to 5 cm.
  3. Then, pour the clean water into the jar. 
  4. Cover the jar with a rag and let it sit for 3 to 5 days to brew.
  5. Remember to stir the mixture a few times every day.

Many growers believe that one can make good banana tea by boiling a banana in water. But this is a bad idea. The banana may lose nutrients entirely due to high temperatures.

Instead, choose to always cold brew your banana tea, which lets the peels pass on the nutrients to the water due to bacteria growth.

Also, when the tea is brewing in the jar, you may notice some gas in it — this is normal. However, if the gas smells acidic or rancid, you must discard it and start again; the tea should smell like a banana.

Once the tea is ready, follow these steps to feed it to your plant:

  1. Strain the tea to remove any pieces of the peel.
  2. Dilute the tea in water in a 1:10 ratio.
  3. Once a week, water your plant with the tea.

The banana peel tea contains enough potassium and phosphorus to give your plant a boost for some time. Plus, it has various microbes that are good for your growing medium.

5. Wood Ash

You can even use wood ash to give your grow medium a potassium boost. We know wood ash is a touchy subject — it produces a lot of salt and lime that can alter the medium's pH balance and burn the roots.

So, only use wood ash if you grow an outdoor cannabis plant on the ground. Wood ash can significantly damage the root zone of hydroponic plants.

Here is how you can use wood ash to fix potassium deficiency in your outdoor plant:

  1. Collect the finest wood ash you can find — you can get this at your local horticultural store.
  2. Sprinkle some wood ash on the soil to do a patch test.
  3. If all goes well, increase the dose and sprinkle more of it around the plant.
  4. Do not sprinkle the ash on the plant, especially the flowers, and avoid covering the entire soil.
  5. Then, water the plant like you would.

Wood ash contains high potassium levels, and it tends to stay in the soil for long. So, sprinkling some on the earth will keep distributing potassium for many days. 

Even if your plant recovers, you can still sprinkle little wood ash on the medium during the first week of bloom to get bigger, bushier buds!

6. Use Bone Meal

You can even use bone meal to fix potassium deficiency in your cannabis plant. Bone meal is nothing but finely ground animal bones, usually beef bones, and has been used as a fertilizer for many decades.

This meal is rich in phosphorus and potassium, and since it's natural, it is also relatively safe for cannabis plants.

The best thing is that a decent amount of bone meal can last for the entire growth cycle since it does not dissolve in water but keeps dissipating nutrients for a few months.  

You can buy bone meal from your nearest gardening supply store, but the directions for use may vary from brand to brand. Usually, the bone meal is supposed to be either mixed with the growing medium or sprinkled over it.

The best time to use bone meal is before switching the plants to the flowering stage.

If you are a vegan, you may not like the idea of supporting this product. In that case, you can use kelp meal.

Also, bone meal is dangerous for pets, so avoid using it if you have a pet that likes hanging out in your grow room.

Prevent Potassium Toxicity or Burn

In the process of fixing potassium deficiency, many growers overcorrect their approach to cultivation, which can lead to potassium toxicity. Too much potassium isn't good for the plant as it can cause various problems like:

  • Manganese, calcium, or other trace element deficiency as too much potassium inhibits micronutrient absorption in the roots.
  • The root zone may turn acidic.
  • The leaves may develop burns, brown spots, or have thin blades. 

So, do not be hasty in fixing the problem. Instead, always work your way up to the solution to ensure your plant gets a healthy dose of potassium boost and nothing more. 

Recovery Time

Your plant's recovery from potassium deficiency depends on your method of solution. Typically, you can resolve the issue within a week. 

However, the damaged parts of your plant may not recover. If the leaves are extensively damaged, trim them off.

Remember to check your plant even after the plant has recovered for any signs of potassium deficiency. 

Summary: What is Potassium Deficiency? And How Do You Fix It?

Potassium deficiency is a fairly common problem that many growers face with their plants, and it can potentially affect your harvest's quality and yield. But thankfully, it is pretty easy to fix.

First, you must learn the symptoms of potassium deficiency and compare them to other deficiency symptoms. 

Second, try to figure out the cause of the deficiency and fix it so the problem does not get worse.

Third, choose a way to give your plant a potassium boost by using bloom boosters, wood ash, or bone meal. 

Also, the most important thing you can do while growing cannabis is to inspect the plant daily. Look at the underside of the leaves, measure the EC, PPM, and pH levels, and collect as much data as you can about your plant's health.

Doing so would give you a deeper understanding of your plant's health and spot problems even before they become visible. 

Keeping a close eye on your plant's health is the first step in avoiding problems like potassium deficiency that take some time to show up on the plant and cause irreversible damage.




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Excelente información como la que brindan todas las semanas! Me gustaría leer algo sobre las enzimas! No encontré nada en el blog.
@JuanHaze_Arg, will defo create one for enzymes. Thanks for the idea!
Nice write up, thank you 😀