Deficiency and excess of Potassium in cannabis plants

Potassium

There are many nutrients that influence in the development of marijuana plants; on this post, we are going to point out the most important functions of Potassium. We will tell you how to treat deficiencies and excesses of this element and the effect it has on the plant metabolism, especially in cannabis plants.

potasio 1

Potassium

Potassium is an element found in the land in mineral form. This mineral is more or less present according to the type of terrain. Soils composed of clay are by far the richest ones in potassium, containing up to a 3%.

The potassium cycle

This element arrives at the oceans and seas through rain, aquifers, rivers, etc, where it returns by evaporation to the sky in the form of water vapour. This vapour condensates and returns to Mother Earth in form of rainfall..

One of the ways that potassium has for its self-regeneration in the land is through animal droppings. Potassium returns to dry land to be processed again by micro-life. The remains not used by plants will be swept away by the rain and led through aquifers into the seas and oceans to return again to solid ground and close the potassium cycle.

In those regions with constant rainfalls, the substrate doesn’t properly retain this nutrient, so it isn’t found  in the substrate in sufficient quantity for plants. Potassium is easily carried away by water, so we should add potassium in the form of sulphates to out nutrient solution in order to make it available for plants.

Functions of potassium in cannabis plants

Onset of the deficiency

Early stage of potassium deficiency

Potassium is one of the most important nutrients for marijuana plants, and although it doesn’t have much presence in the plant tissues it performs important catalyzer functions in many metabolic processes as those we list below:

  • It takes part in the photosynthesis process improving the synthesis carbohydrates.
  • It participates in the synthesis of proteins and amino acids, which come from nitrogen in the form of ammonium, so the interaction between these two nutrients is vital to perform different metabolic processes of plants.
  • It improves the resistance of plants during drought periods.
  • It increases the consistency and strength of the plant tissues.
  • Together with Phosphorus, it improves  the strength and resistance of the root system.
  • The resistance against frost is also increased by acting in the sap of the plant.
  • It increases the weight, density and volume of the buds.
Intermediate stage of potassium deficiency

Intermediate stage of potassium deficiency

If there is a potassium deficiency, plants will have visible symptoms that will help us to detect it. Potassium is a mobile element so it moves from older to younger leaves when needed, since the top part of the plant has always more metabolic activity. We should make sure that our plants have enough Potassium during their life, since any lack of this nutrient will be translated into lower yields.

In the case of having potassium deficiencies, you should add more fertiliser (rich in this element) either from organic or mineral origin. Organic fertilisers are more slowly processed than mineral nutrients, which will correct this deficiency in no time and will allow you to harvest decent buds. If the deficiency is at an early stage you can simply increase the dose of your organic or mineral nutrient, what will probably solve the problem.

Advanced stage of Potassium shortage

Advanced stage of Potassium deficiency

Potassium deficiency in cannabis plants

Visible symptoms in cannabis plants:

  • The leaves turn yellow from the tips towards the centre, ending at the base of the leaf.
  • Plants are weak and have little resistance to diseases.
  • Stems are also weak and bend easily.
  • The final yield of buds is seriously reduced.
  • An excess of calcium can lessen the capacity of the plant to absorb potassium, leading it to a deficiency of this element.

Potassium excess

Symptoms of potassium excess:

  • Blocks the absorption of other elements such as calcium, magnesium, zinc and iron.
  • Given this situation, you should flush the roots with at least triple the amount of water than the capacity of the pot; you can also add any component that helps to flush the salts away and leach the substrate. Then, you should water with a light, complete and balanced nutrient solution.
Foto 1: Potassium deficiency

Foto 1: Potassium deficiency

The plant in the picture #1 presented a potassium  deficiency that has been treated on time, without losing much bud yield and quality.

This marijuana plant was grown in an inert medium – coco-coir – and suffered a deficiency during the flowering stage, when potassium is more needed, during the 6th and 7th weeks (This plant had a flowering period of 8-9 weeks)

In the picture #2 we can see how the plant has suffered a more serious potassium deficiency.

At medium height of the plant we can see how the tips of the larger leaves are burned. Moreover, you can see with ease a discoloration of the leaves to a more yellow colour.

Photo 2: Potassium lack

Photo 2: Potassium deficiency

At the top of the plant we can easily detect that the plant has been negatively affected by this deficiency. The buds couldn’t develop completely and have remained in a quite decayed condition..

The buds of this plant won’t have superior smell or flavor since potassium is essential in terpene production.

At this stage, if you didn’t provide the necessary nutrients the yield will be seriously decreased. The buds won’t be compact and the resin production will be minimal.

Photo 3: Potassium deficiency on intermediate phase

Potassium deficiency

These deficiencies are usually more evident and frequent in Indica strains, which are often grown without much knowledge since their flowering stage is much faster than Sativas, and the maximum demand for potassium is centralized in no more than 1-2 weeks, depending on the strain.

Since Sativa plants take much longer to flower, their nutritional needs are more progressive than in the case of Indica genetics. Still, it should be noted that Sativa strains are more susceptible to be over-fertilised than Indicas, so you should pay close attention to their needs to have a crop free of deficiencies and excesses.

In this way, choosing a balanced hybrid strain will help  to control any excess or deficiency of potassium and other minerals like nitrogen or phosphorus.

15 Comments


15 comments on “Deficiency and excess of Potassium in cannabis plants

  1. Papa Indica

    Very good articles on deficiencies, thank you!

  2. Robert Shackleferd

    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.

    1. Dani Alchimia

      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!

  3. KIrk Perry

    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!

    1. Dani Alchimia

      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!

  4. Brent

    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.

    1. Dani Alchimia

      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 dani@alchimiaweb.com

      Best!

  5. Allan Soler

    Can I fix a potassium deficiency with potassium silicate?

    1. Tim Alchimia

      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!

  6. Mark

    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!

    1. Tim Alchimia

      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!

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