potassium cannabis

Excess or lack of potassium in marijuana

Chemical symbol for potassium with two cannabis leaves

The symptoms of a deficiency or lack of Potassium in marijuana plants are easy to recognize, as long as you’ve read this article before of course… So, I’ll explain you how to identify this nutritional problem.

🚀 Lack of Potassium Symptoms

  1. Older leaves start yellowing from the tips inwards
  2. The stems and petioles of the leaves weaken and cease to be erected.
  3. Plants become more vulnerable to pests and diseases
  4. Development rate slows down, affecting final production

Image of a cannabis plant affected by a severe potassium deficiency*

Now we are going to take a closer look at each of these points, to facilitate the task of identifying a Potassium deficiency in cannabis.

1 Why do you see it earlier in the older leaves? This is because Potassium is a macro-element, and these are mobile within the plant, so when it lacks to form new shoots, it takes the stock from the lowest leaves.

2 The stems and petioles of the leaves lose strength for several reasons, the main one being malnutrition itself, but they are also weakened by the inability of the leaves to carry out photosynthesis properly.

3 Many times the lack of nutrients in weed is associated with other misfortunes, such as pests and fungi attacks. This is because when the plant is healthy it has a much stronger immune system, just as it happens to us humans.

4 When cannabis plants are healthy, it is almost as if their growth can be seen with the naked eye, it is the plant that develops fastest. But that speed slows down drastically when they lack some macronutrient, something that is easily perceived.

✅ What causes lack of Potassium?

  1. Poor substrate quality
  2. Inadequate PH
  3. Excess Calcium blockage in irrigation water or substrate
  4. Lack of Potassium in the nutrient solution
  5. Blockage by excess of salts in general

As a general rule, when we suffer a deficit of Potassium in cannabis crops is for one of those 5 reasons but, why does this happen?

1 We all have met a grower friend who, by trying to save some money on substrate, ends up buying a low quality one. This is a big mistake, you save a small amount and it will usually cause you problems, so we strongly recommend growing with quality soil.

If we cultivate with a quality substrate and detect that the plant lacks Potassium, it can only be for one of the other 4 points. What we usually do is discard until we find the problem, more or less like doctors do.

2 The pH of irrigation water is very important for the absorption of nutrients. Potassium has an optimal pH range between 6.1 and 7.1 approximately, so values above or below that range can cause a lack of K.

3 An excess of Calcium can cause a lack of both Potassium and Magnesium. The balance between the elements that nourish the cannabis plants is indispensable, because some are antagonists of others, and when there are excesses of ones they can provoke the blockage of others.

4 All the cannabis varieties do not eat the same, in nature the Landraces have been adapting to their environment over the years. But today most commercial genetics are hybrids and polyhybrids, with different nutritional needs. Sometimes it happens to us that because we are afraid to use too many composters, we give them less fertilizers than plants need at that moment, causing a deficit of Potassium among other disorders.

5 This usually happens in crops where the plants have been in the same pot for a long time. It is due to the accumulation of salts in the root system, since roots do not assimilate the whole fertilizer, and the excess remains in the substrate, which gradually interfere with the perfect absorption of nutrients. The use of Enzymas and root washing corrects this problem.

Image where you can see the evolution of a lack of Potassium in cannabis leaves

🔥 Too much potassium in the marijuana plant

Besides the lack of potassium, it can also be in a situation of excess thereof, therefore, blocks the absorption of other minerals, such as calcium, magnesium, manganese, zinc or iron..

This excess, visually, causes the plant has a much darker color. If in the case of lack plant was becoming yellowish, in this case it turns dark brown. In addition, it will give way to other multiple deficiencies caused precisely by this overfertilization.

If this is your case, but still time to save your plant because this is not dead or has not been greatly affected, you must take charge and give you a solution. Is there any perfect? The word would not be perfect, but simply a quick and effective response to the problem that your plant right now.

Thus, in these cases, the solutions to follow are the following: firstly, a wash of roots, so that they can return to absorb all the nutrients. They are getting your plant develops as expected it. Some may even improve many of the processes that follow the plant until we collect the fruits expected during harvest. Returning to the subject of washing, it is recommended to do so with at least triple water capacity of the container.

During this root cleaning, we can also add an enzyme solution to the water with which we water our plant, helping to break down the salts and thus leach the substrate. Once this step has been carried out, it is recommended to water with a light and complete fertilizer.

Do you recognize with the naked eye a lack of potassium in cannabis crops? ⚠️ In this article we easily show it to you ✨ It will never affect you again.

Potassium Deficiency In Cannabis Plants – A How-To Guide

With potentially deadly consequences and a higher chance of appearing in the flowering stage, a potassium deficiency can be dangerous. Make sure you’re prepared to prevent and even solve it if a deficiency arises.


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.


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?


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!

Nutrient deficiencies are a very common problem amongst growers. This one, however, might have dangerous consequences if not taken care of in a timely manner.