By RQS Editorial Team

Browse Deficiencies
Browse Deficiencies
Browse Deficiencies


Just like you and I, all living things require a very specific set of conditions to survive. But survival is not the only factor to take into account when growing cannabis. In order for plants to yield the best buds they can, you’ll have to take extreme care to ensure a thriving crop. This includes noticing deficiencies in time to correct them. Today, we’ll be covering just one - potassium deficiency -, although the procedures are similar amongst many different deficiencies.

Potassium Deficiency In Cannabis Plant


In cannabis, potassium is essential for many important functions. It takes part in the photosynthesis process, which gives the plant its green colour, and is crucial to plant health and development. During a drought period, potassium is the nutrient that improves a plant’s resistance, not that you should go any period without watering your plant. This is more important for cannabis that grows freely in nature as it’s responsible for aiding the movement of water through the plant.

In conjunction with phosphorus, potassium increases the strength and resistance of the root system as well as the plant’s tissue. This will also help protect the plant from harsh, cold weather.

Considering all these factors, it’s clear to see how potassium is essential for your marijuana plants. However, your average grower will give more importance to how this nutrient affects the buds of the plant. Potassium is a nutrient that helps increase the weight, density, and volume of your delicious nugs. This is why being able to recognise and fix this deficiency is an important skill to have as a grower.


It’s important to note that if you are currently handling plants in a hydroponic system, you won’t have to worry about this. Potassium deficiencies are extremely rare in water-based systems. If you have similar visual symptoms, make sure you double check your system before treating it for this problem.

Deficiencies do happen in soil and other mediums every so often. The most common symptom you’ll notice is a brown or yellow colouring in the tips and edges of the leaves. With the passing of time, these will curl up, appearing burnt - much like an iron deficiency. Another thing that will raise suspicion is stretching. If one plant seems to be taller than the others around it, it’s not a good sign as this weakens the stems.

The appearance of spots on the leaves will be the symptom to follow. Firstly, you’ll see those necrotic spots characterised by their brown tonality. Left untreated, more spots will begin to show. This time with chlorotic ones, characterised by a white colour. The veins of the leaves will keep their green colour, unlike many deficiencies. What you’ll notice shifting colour are the petioles and stems, now showing red tones.

Although previously, you might’ve noticed the plant stretch out, it was not growing. This deficiency slows down plant growth. Leaves will grow small in size, and this is when the deficiency becomes most dangerous. Potassium shortages are very mobile. They move around the plant very fast, unlike most deficiencies. This one will spread to the larger fan leaves where it will most likely kill them.


Before implementing any changes to your grow medium or watering solution, take a look at your lights. With strong LED and HPS grow lights, you might be overheating the leaves. These will show burn symptoms even if the overall temperature is cool. Just make sure you check for this first. Move your plants further away from the lights for a couple of days to determine the root of the issue.

In case lights are not the problem, the deficiency might be caused by an excess of fertilizers and nutrients. Excess salt is especially common as it tends to build up in the growing medium.

Nutrient lockout is a very common cause of most deficiencies. When the pH of the soil is too low, it makes the medium too acidic. This causes stress in the root zone and prevents the uptake of potassium. How can you stop this?

Potassium Deficiency in Cannabis Leaves


When it comes to the pH issue, make sure you establish and maintain a healthy pH throughout the entire life cycle. In soil grows, the pH value should be fairly neutral, between 6.0-7.0 for the optimal potassium uptake. As for hydro systems or coco coir, a slightly more acidic pH would be recommended. Between 5.5-6.5 is ideal for this. To fix pH issues, make sure you flush your medium. Use neutral pH water to remove the excess nutrients in the soil. Only include half of your usual nutrient solution in the water.

You might also be overwatering your plant. Proper watering practices will go a long way in keeping a plant healthy. The method and frequency with which you water will impact your future buds massively. Don’t overlook this.

Make sure you read the labels of your supplements to see how these nutrients interact with each other. Too much of some will lock out others. Calcium and nitrogen will decrease the absorption of potassium, for example. Just be sure not to use too much of something without a full understanding of what it does.

You can always use a supplement rich in nitrogen, phosphorus, and potassium. Only do this after you’ve flushed the plant. Give the plant time to recover and be on the lookout for the newer leaves and how they grow.

When plants suffer from a nutrient deficiency, they are weak and have little resistance to disease. This is why it’s important to know how to detect and fix the deficiency in time. Potassium is essential for terpene production. If not enough is supplied, your buds will lack flavour and smell. The flowering stage is where you’ll most likely face a deficiency like this.


Hopefully, you’ve learned more about potassium deficiency and all deficiencies in general. Next time, you’ll be able to fix this problem comfortably and in a timely manner. Only through experience will you be able to obtain the best yields you can. Deficiencies are reversible and easy to solve if you know what you’re doing, and now you do. Best of luck with preventing and solving potassium deficiency!


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