As a budding grower, you have two ultimate goals: obtain the highest quality weed possible from a bountiful yield. 

The best way to reach this goal is by ensuring your plant’s overall health by maintaining a sufficient nutrient balance. 

When it comes to yield and flower quality, potassium reigns supreme. 

While you shouldn’t ignore any nutrient, potassium keeps your plants strong and disease-resistant. It also contributes to a high-quality, high-yield harvest. 

Join us as we learn how to spot potassium deficiency in your cannabis plants. We’ll also guide you in solving and preventing potassium deficiencies in your weed in the future.

Before getting into the weeds (excuse the pun) on this, you should understand the role of nutrients like potassium in healthy cannabis crops. 

Let’s get straight to it.


What does potassium do for cannabis plants?

Nutrient deficiencies in weed can be the bane of any grower’s life. They can cause your weed to become susceptible to disease and infection and seriously hinder the plant’s growth. 

It’s important to note that sourcing good seeds with a strong and tested genetic profile can help avoid these problems altogether

We’re going to look at potassium deficiency in weed today. 

Potassium takes its place alongside nitrogen and phosphorus as one of the “big three” nutrients essential for all growing plants. These three nutrients are found in all plant fertilizers in varying ratios referred to as “NPK.” 

Briefly speaking, these three nutrients confer the following benefits;

  • Nitrogen (N) is essential in making sure plants are healthy as they develop. That’s because nitrogen is essential in protein formation and makes up much of the tissues of most living things. 
  • Phosphorus (P) is linked to a plant’s ability to use and store energy, aiding photosynthesis. It also helps plants grow and develop normally.
  • Potassium (K) is the third key nutrient of growing crops—and our focus here today. Potassium in cannabis helps strengthen the plants’ ability to resist disease and increases your yield and quality. Potassium also improves the plants’ response to harsh or cold conditions and strengthens their root system.

While all three nutrients are crucial, we can see that potassium has a positive impact on both the yield and the quality of your harvest

Should your growing crop develop a cannabis potassium deficiency, you might see a reduction in yield and a drop in marijuana quality. 

Let’s move on and look at some general information on nutrient deficiency and then focus on cannabis potassium deficiency.


Potassium Deficiency in weed


General NPK deficiency information

Growing plants certain levels of NPK to thrive. Without access to these three nutrients, plants will display various signs and symptoms of a particular deficiency. 

These symptoms vary somewhat, but we have a general overview of what to watch out for to spot cannabis deficiencies;

  • Nitrogen (N) Cannabis Deficiency: Plants may begin to turn pale green, and older leaves begin to turn entirely yellow in a process called “chlorosis.” Plants become stunted, and new growth is spindly and weak.
  • Phosphorous (P) Cannabis Deficiency: Plants may begin to develop brownish or purplish spots on the underside of larger, older leaves. Growth is slowed dramatically.
  • Potassium (K) Cannabis Deficiency: Plants begin to display yellowing or scorched leaf edges and may begin to shed leaves as they experience necrosis. It’s essential to identify this deficiency early and keep it under control.


Symptoms of potassium deficiency in weed

Let’s take a closer look at the most common symptoms of marijuana potassium deficiency. It’s important to note that you’re most likely going to face a potassium deficiency during flowering, as opposed to the vegetative phase. 


Slow Growth

One of the main impacts of potassium deficiency in marijuana is a reduced growth rate. This can be difficult to spot as your plant may have already stretched in response to its deficiencies.

While stretching may give the impression of a healthy growing plant, it can weaken stems leading to further problems at a later stage. This stunted growth will, in turn, lead to our next symptom.


Small leaves

Once a plant is experiencing stunted growth because of a potassium deficiency, you may notice that new leaf growth is small and stringy

While the potassium deficiency in your weed is causing stunted new growth, it can also move through the plant and cause other problems.


Potassium Deficiency in weed


Yellow or brown leaves

The next most common symptom of potassium deficiency in weed usually occurs following the above-mentioned stretching and stunted growth. 

Fan leaves begin to show yellow or brown discoloration on the edges and tips of leaves, and brown spots appearing on the underside of fan leaves.


Burnt leaf tips

As the K deficient cannabis continues to deal with the problem, the browned or burned leaf edges and tips will begin to curl up and die

This can be very problematic, as with reduced growth and the loss of older, larger fan leaves, a plant can quickly find itself in a very bad spot.

A common, and understandable mistake made by many growers is to conclude that your plants are too close to your light setup. 

Indeed, the symptoms are so similar that it’s important to eliminate the possibility of light burn on your plants before you alter their nutritional intake.


Could your problem actually be light burn?

The symptoms of potassium deficiency in cannabis can easily be confused with those of light burn. 

Before you set about trying to remedy the situation by changing the plant’s nutrient intake, understand and eliminate the possibility of light burn.

With higher wattage light setups, LED and especially HPS lights, it’s important to keep them at a good distance from the top of your plants. This isn’t something you should get lazy with, as plants can show burn symptoms even if temperatures are not that high.

As a general rule of thumb for LED setups, you should have them 12 inches away from the plants during vegetative stage, and 18 inches during flowering

If you’re using a HID or HPS light setup, you should increase these distances.

If your plant still shows signs of leaf “burn” after ensuring a safe distance from the lights, it can only be a sign of potassium deficiency.


How to fix potassium deficiency in soil

Potassium deficiency in cannabis plants is most commonly found in grow set-ups using soil as a medium—they’re much less common in hydroponic setups.


Use good quality nutrients

This is probably the first and the best course of action to treat potassium deficiency in soil. Ensure you’re using a reputable and appropriate set of nutrients. 

By doing some research, you’ll understand that too much of a particular nutrient can prevent the efficient uptake of other nutrients. Ensure that you use a high-quality, balanced nutrient program for your crop.


Adjust the pH range

One of the main causes of potassium deficiency in marijuana is nutrient “lockout”. This happens when the pH levels of the soil become too acidic, leading to a difficulty in nutrient absorption for the plant. 

While you may be feeding the plant correctly, the plant will be unable to access the nutrients in the soil if it isn’t sufficiently pH balanced

To avoid this, it’s important to monitor and adjust your soil pH levels as needed. In soil, we’re looking for a pretty neutral pH of 6.0–7.0 to maximize potassium uptake.


Flush your plants

If you find that your pH levels are not balanced correctly, the first course of action is to flush your soil medium to remove excess nutrients. 

This can be done by watering your plants with neutral pH water and half your normal nutrient solution added to the water.

Flushing your medium is the nearest thing to a “reset” button and treating potassium deficiency in your weed.


Monitor leaves

The next step is to carefully monitor leaves for further signs of potassium deficiency. 

Remember, the telltale signs of this are progressively burnt or browned leaf edges and tips, which eventually begin to crisp and curl up.

Carefully monitor the leaves each day to help you identify and treat the problem early.


Potassium Deficiency in weed


How to fix potassium deficiency in hydroponic setups

While potassium deficiency in cannabis is uncommon in hydroponics, it isn’t impossible. Let’s look at the steps you should follow for this medium.


Use the best hydroponic nutrients

As with soil, the first step is to research high quality hydroponic nutrients. With so many reputable products on the market,it’s relatively easy to get a good balance of nutrients for your cannabis.

Try to stick to a complementary set of nutrients—mixing and matching brands may lead to overlapping nutrients and ultimately nutrient toxicity or reduced uptake in your plants.


Amend pH levels of water

Just as when using a soil medium, it’s crucial to monitor and adjust the pH levels of your hydroponic system.

You should still maintain a pretty neutral pH level in a hydro setup, just slightly more acidic. Ideal ranges are about 5.5–6.5 for a soil-less or hydro setup.


Use seaweed or other natural potassium sources

Further steps to supplement potassium uptake include using natural sources such as seaweed or kelp. You could also use a natural foliar spray instead of a medium.


Preventing potassium toxicity

Now that you know how to identify and treat potassium deficiency in marijuana, let’s look at how to prevent it. It’s essential that you avoid over-correcting in your approach as it may lead to potassium toxicity in cannabis.

Too much of any nutrient may be just as detrimental to a plant’s growth as too little. An overabundance of one nutrient may prevent the absorption and uptake of others. 

Telltale signs of potassium toxicity include leaves turning a dark brown color, instead of the pale yellowing of leaves in the case of deficiency.

The simplest way to prevent this situation is to carefully monitor nutrient levels, and incorporate regular flushing. This breaks down any nutrient build-up in your medium. 


Healthy plants mean hefty harvests!

You now know how to identify and treat potassium deficiency in weed. With some care, attention, and a little bit of luck you’ll be growing beautiful healthy cannabis plants without fail.

With the knowledge of how to fix potassium deficiency in plants, you’ll be on your way to happier, heavier harvests!

Also remember, growing strains with strong genetics will result in hardier, more disease-resistant plants. By choosing your seeds carefully, you can reduce many of these issues from the beginning.

Posted in: Grow TipsTips View all