Excess or lack of potassium in marijuana

Reading Time 5 minutes


Chemical symbol for potassium with two cannabis leaves
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*
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
Image where you can see the evolution of a lack of Potassium in cannabis leaves


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🔥 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.



root cleaning
Root cleaning


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.



🎯 Why is Potassium so important in cannabis nutrition?



  1. It is responsible for the weight, density and hardness of the buds.
  2. Improves the resistance of plant tissues
  3. Promotes the synthesis of carbohydrates during the photosynthesis process
  4. Improves root system strength and development
  5. It is involved in the synthesis of proteins and amino acids.
  6. It favors the plants’ resistance to frost or drought


Potassium is a mineral that can be easily found on many external soil where we cultivate our marijuana plant, especially on clay, but the same in those lands where abundant rain not occur and therefore, the substrate can not retain good of all this nutrient, so if we cultivate marijuana plants there, even outdoor, you will not have a sufficient level of potassium is needed for our plant to develop properly.

The same goes, of course, in cultured interior where, in itself, there will be no trace of potassium, except you can carry the soil on which we cultivate our plant, but never be sufficient and, therefore, we add to fresh land we use, as one of the multiple supplements to be added to the fertiliser of the same.



Infographics on Potassium Excess and Deficiency in a Cannabis Plant
Infographics on Potassium Excess and Deficiency in a Cannabis Plant


Why? Because without this product, plant not make it to an end and, if so, the result would not be at all as expected, that is, it would be of very poor quality. That said, it should be noted that the main functions of potassium with respect to the marijuana plants, are: involved in plant photosynthesis, contribute to it getting carbohydrates that it needs; It acts at the time of synthesis of proteins and amino acids; It contributes to increased plant size, as well as the improvement in density and volume thereof; when the plant is facing periods of drought, it gets stronger and its growth is not altered by this inclement weather; strengthens the root system, while increasing the hardness of tissues.


Canna Potassium 20%


This liquid additive can be mixed with any fertilizer...

This liquid additive can be mixed with any fertilizer, we can use it in the growth and flowering phase, covering the potassium deficiencies of the cannabis plants…

Canna Potassium Characteristics 20%

1-2 ml per 1 litre of water.

-Care: The concentrated form of Potassium cannot be mixed with fertilizers containing calcium and potassium.

More information about
Canna Potassium 20%


Potassium is therefore one of the most important nutrients in developing plant seeds, especially in early culture, but also in the flowering period where proper use improve product quality to obtain, in addition to increase the resistance of the plant and the volume of the buds, as we mentioned above.



I’m sure that after reading this article you will improve the yield and quality of your crop, so we would appreciate it if you could share it in your social networks.😜 We thank you in advance.


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Fran Quesada Moya
Fran Quesada Moya

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