Deficiency and excess of Potassium in cannabis plants

In the complex cocktail of essential elements for correct plant development, potassium stands out as a vital director that orchestrates numerous fundamental processes in plant cultivation. In today's article, we are going to see the main characteristics of potassium, exploring its crucial role in strengthening cellular structures, regulating water balance, and enhancing resistance to environmental factors.

In addition, we will also see the main symptoms of a deficiency or excess of this element, known for its impact on the health and vigor of plants, and which plays a transcendental role in numerous plant vital processes.

 Potassium is essential in various metabolic processes of cannabis plants (Image: Jeff W)
Potassium is essential in various metabolic processes of cannabis plants (Image: Jeff W)

The Potassium Cycle

Potassium is an element that we find on Earth in the form of a mineral. This mineral is more or less present depending on the type of land in which we grow. Soils composed of clay are by far the richest in potassium, which can contain up to 3%.

Through rain, aquifers, and rivers, this element goes to the oceans and seas where, by evaporation, it returns to the sky in the form of water vapor to pass again in the form of precipitation to the mother earth.

One of the ways that this element self-regenerates on Earth is through animal excrement. Potassium returns to dry land to be processed again by soil microbial life. The remains not used by the plants that have been washed away by the rain return through the aquifers to the sea and oceans to be returned to the earth again and close the potassium cycle.

In those regions where rainfall is constant, the substrate will not have good retention of this nutrient, and consequently, it will not be found in the substrate in the quantities that the plants demand. It is a very easy element to drag with large amounts of water. Thus, we must add potassium in the form of sulfate to add this element back to the substrate and make it available to the plants.

Products to enhance microbial soil life

Feeding the soil is crucial to achieve best results when growing organic cannabis. In this article we tell you how to do it and what are the best products to enhance the microbial soil life, which highly improves nutrient uptake and has a direct impact on the overall performance of your plants.

Functions of potassium in marijuana

Potassium is one of the most important nutritional elements for marijuana plants, present in all types of fertilizers and additives, such as PK boosters. Although they are not so present in plant tissues, they do perform important functions as a catalyst for many metabolic processes such as those we can see below:

  • It intervenes in photosynthesis, promoting the synthesis of carbohydrates.
  • It intervenes in synthesizing proteins and amino acids which come from nitrogen in the form of ammonium, so the interaction between the two nutrients is vital to carry out the different metabolic processes of plants.
  • Increases the plant's resistance in periods of drought.
  • Increases the consistency and hardness of plant tissues.
  • Together with phosphorus, it increases the hardness and resistance of the root system.
  • Frost resistance increases by acting as an antifreeze, acting within the plant sap.
  • Increases the weight, density, and volume of the flowers.

Potassium deficiency in cannabis, early stage
Potassium deficiency in cannabis, early stage

Potassium deficiency in marijuana plants

In the case of a Potassium deficiency, the plants will have visible symptoms that will help us detect said deficiency. This is a mobile element so that when the plant needs it, it will move from the oldest leaves to the youngest, always being the part of the plant with the most activity in its metabolism. We must ensure that this nutrient is not lacking in crops since a visible and advanced potassium deficiency means that the plant's production will already have been reduced.

In the case of potassium deficiencies, we must add more nitrogen fertilizer, whether of biological or mineral origin. Organic fertilizer is slower to absorb than mineral fertilizer, which in a short time will have been able to solve this deficiency and be able to harvest some decent buds. If the deficiency is premature we can simply increase the dose of fertilizer in organic or mineral format according to the preferences of each grower.

 Middle phase of potassium deficiency
Mid-phase of potassium deficiency

Symptoms of potassium deficiency:

  • The tips of the plants turn yellow and this spreads towards the center, ending at the base of the leaf.
  • The plants have no vigor and have little resistance to diseases.
  • The stems are weak and bend easily.
  • The final production of buds is seriously reduced.
  • An excess of calcium can reduce the plant's ability to absorb potassium, creating a deficiency.

 Advanced phase of potassium deficiency
Advanced phase of potassium deficiency

Excess potassium

Excess potassium in plants can manifest itself through various symptoms. Here are some common signs of too much potassium.

Symptoms of excess potassium:

  • Marginal chlorosis: Leaves may develop chlorosis, a generalized yellowing, with a dark green edge.
  • Leaf necrosis: Brown spots or necrotic areas may appear on the leaves, especially on the edges.
  • Decreased absorption of other nutrients: Excess potassium can interfere with the absorption of other essential nutrients, such as magnesium, zinc, iron and calcium, leading to deficiencies of these elements.
  • Reduced growth: Although potassium is necessary for plant growth, too much can inhibit the absorption of other nutrients and negatively affect overall growth.
  • Reduced cold tolerance: Plants with excess potassium may become more susceptible to cold damage.
  • Nutritional imbalances: An excess of potassium can cause nutritional imbalances since it can displace other cations in the plant's absorption.

Please note that symptoms may vary depending on the variety and specific growing conditions. Carefully monitoring plant health and adjusting fertilization rates as needed is key to preventing problems associated with excess potassium.

To treat an excess of this element, a root wash must be carried out with a minimum of three times the water capacity of the pot, aided by enzymes, which will act as a salt breaker. Subsequently, we must water with a light, complete, and balanced fertilizer, always adjusting the pH according to the phase in which the plant is.

Happy harvest!

The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “Deficiency and excess of Potassium in cannabis plants” (13)


Frederiko 2023-10-24
Good afternoon. Some of my plants have red petioles and the stem of the plant. Maybe you can help with advice on what the plants are missing?


Plumsmooth 2022-04-11
believe it may be cumulative in that my use-age of heavy boost Calcium final weeks of Veg has led to an immediate deficiency when switching the lights to 12/12? lasting through he stretch. In other words the lockout is present in the meristem etc?


Smokestacks Is an Alchimia client 2021-03-13
Love the article! I run Michigan mix M3 soil. It's considered a super soil. I always seem to run out of potassium around the end of the stretch in flower. In five and 7 gallon felt pots too. I add beneficial microbes to the medium. I ph and all that when I water, reading the comments I realized that a lot of potassium gets flushed out basically when I water. Can I just add like a bloom dry amendment. Like roots organics bloom or should I localize the problem with something like kelp. I'm also seeing what looks like cal or mag defencie. Maybe because potash aids in the delivery of those micro nutrients. Can I over feed when using organic amendments?

Alchimia Staff

Tim Alchimia 2021-03-16
Hi and thanks for your comment. I think that top-dressing with a dry flowering amendment would be your best option. I tend to keep adding fertility to the soil surface throughout the flowering period, at least until around 3-4 weeks before I expect to harvest. It's definitely a balancing act though, as it is certainly possible to overfeed with organic amendments. I always work by the rule that we can always add more fertility if necessary but removing it once applied is almost impossible, so tread carefully! I hope that helps, best wishes and happy growing!


Teab ag 2021-02-11
Hey Just wondering can you over pot ash a plant? Have a few in the back yard and just want to crank them but nervous on over cranking. Also useing the worm tea from worm farm and a general slow release fertiliser was in the start mix up. Cheers heaps

Alchimia Staff

Tim Alchimia 2021-02-11
Hi, thanks for your comment and question. Like any nutrient, it's possible to overdo it with Potassium, although it's certainly much less of a problem than, for instance, Nitrogen, especially if all other factors, such as pH, are in order. Potassium is readily soluble in water so it's not difficult to flush from the substrate. Bear in mind that plants won't really need high doses of Potassium until the flowering period, and gradually increase the rate of application and keep an eye out for any signs of toxicity. I hope that helps, best wishes and happy growing!


whatnot 2020-07-10
Hi.. I have NL Autos in pots - currently flowering - and put some ( handful) of wood ashes in the pots and watered them.. A day later I see burn... Freaked out a bit and then did a flush with lots of water.. My questions are - did I ruin them by giving too much potassium during flower, and did I make it worse by soaking them with so much water

Alchimia Staff

Tim Alchimia 2020-07-13
Hi whatnot, thanks for the comment and question. Yes, it's probable that the excess of K has burnt the plants, one must be very careful with wood ash, and just use a little at a time. It's not a standardised product so the nutritional content can vary greatly from one source to another, meaning it can be very hard to dose. However, you did do the right thing by "flushing" with abundant water, as Potassium is highly water-soluble, so any excess will have been washed away. Of course, it's never ideal to use such large quantities of water on a plant, but given the alternative, it seems to be appropriate here. The plants may suffer a little from overwatering but they will recover. Best wishes and good luck for the rest of the season!


Mmmp_nations_creations 2020-01-11
Helloooo tokers Love all the comments just buying some seeds and checking a few things out, ran crossed deficiencies. Any one has time i ran into this same problem on my YouTube channel. Mmmp_nations_creations


Guy 2019-08-22
Here is useful information about potassium in plants, which is also aplplicable for cannabis:


Mark 2019-06-22
Love those articles and the detailed info you provide to help educate properly, incredibly valuable information you pass along. Please continue to do so! My question concerns composition and various types available, bicarbonate, sulphate, oxide, etc.. I see muriate of potassium frequently when searching for supplies - is this useful for deficiencies? Not familiar with it, wondering if it will work for deficiencies and if it can be dissolved in water for foliar feeding? Thank you for this incredibly valuable service you provide!

Alchimia Staff

Tim Alchimia 2019-06-25
Hi Mark thanks for your question. Muriate of Potassium is another name for Potassium Chloride and it is one of the most widespread potassium fertilisers in use, and, from what I can tell, it is also soluble in water for application via irrigation or foliar spray. Glad to help, all the best and happy growing!


Allan Soler 2018-09-22
Can I fix a potassium deficiency with potassium silicate?

Alchimia Staff

Tim Alchimia 2018-09-24
Hi Allan, thanks for your question. In short, yes, potassium silicate can definitely help to resolve the issue of a K deficiency. However, you may need to look closer at the cause of the deficiency, which may be caused by an incorrect pH level (6-7 in soil and 5.5-6.5 in hydro) in which case you'll need to flush, or by an excess of either Nitrogen or Calcium, which can both impair potassium absorption. Other things that can be useful to resolve the issue are seaweed/kelp, potassium bicarbonate (foliar application) potassium sulphate or potassium oxide. I hope that helps, all the best solving this, and happy growing!


Brent 2017-11-20
I moved my plants indoors with a grow light, at first it grew new leaves and although they are still green the are crinkley and some turned downward at the tips, also my flowers seemed to stop in their tracks. Is my lighting too weak, temp too low, or nutrient deficiencies.

Alchimia Staff

Dani Alchimia 2017-11-21
Hi Brent, I should know what type of grow light you're using, also temperatures and RH levels inside your indoor grow. Many plants turn the tips of their leaves downwards when too much nutrients are being used. If you can, send me a picture of the plants to Best!


KIrk Perry 2016-10-26
I have the same problem with a Tokyo indica. I tested my root ph with an analog (sweep-needle) meter-stick, and after letting the metal shank sit in the day-old watered soil at root level, my ph in all (7) plants measured from 5.1 to 6. The indica affected was the one the measure a ph of 5.1. So, I've read that a better ph reading can be obtained by catching run-off water from the bottom of the 1-gal plastic container? Which is the best method for a true root ph reading? I wish there were a two-piece probe that would open-up once the probe was at root level, so root-soil can be extracted and made into a mud-pie to test, as the meter directions suggest. I need some "root dirt" and nothing else!

Alchimia Staff

Dani Alchimia 2016-10-31
Hi Kirk, Many growers just measure the pH level of the drainage water with a digital pH meter. If you're watering with a pH of, let's say 6, then the drainage water should also be 6. It is one of the best and easiest ways to check if the soil is getting acid or alkaline. Hope it helped!


Robert Shackleferd 2016-06-18
You forgot to mention how important ph is for potassium intake. As soon as i raised my ph above 5.5 i stopped having potassium problems. My leaves looked exactly like the pictures you provided.

Alchimia Staff

Dani Alchimia 2016-06-20
Hi Robert, That's correct, we must always use a certain pH range for proper development of our plants, mainly depending on the growth stage of the plant. Thanks for your comment!


Papa Indica 2015-09-24
Very good articles on deficiencies, thank you!

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