Potassium Deficiency on Marijuana Plants

Hi there and welcome (back) to Free the Tree!
Today we decided to finally cover Potassium Deficiency on Cannabis. We decided to make this article since we just recently went through it on our 2 Big Buddha Cheese’s.
For once, Potassium Deficiency is pretty straight forward. The symptoms are pretty hard to confused with other nutrient deficits.
Let’s get into it!

Leaf half way through Potassium deficiency

What do plants use Potassium for?

Potassium is one of the 3 vital elements that all flowering plants need to thrive. It’s main purpose is helping the Marijuana plant uptake nutrients up from the roots and regulating the photosynthesis process.
Potassium is also used to regulate the opening and closing of the stomata meaning that it handles the CO2 uptake of the plant.

The final use is triggering the activation of enzymes and involved in the production of Adenosine Triphosphate (ATP).
This last involvement might actually be more important in the regulation of the rate of photosynthesis than its role in the activity of stomata’s.

This means that if your plant is suffering from of lack of potassium, she won’t be able to assimilate enough nutrients, regulate well the CO2 intake nor control her photosynthesis… Kind of brutal no?
This deficiency will show itself through the change in color of the leaves, but we’ll get into that in a second.

For more on the role of Potassium in the growth of plants check out this paper done by the International Plant Nutrition Institute, and for more info check out their website.

Here’s a recap of the usage of Potassium in the different stages of life of marijuana

Potassium during Vegetative and Flowering Stages

Stage of Life Potassium (k) Usage in Cannabis
Vegetative Stage
  • Encourages uptake of water
  • Increases resistance to diseases
  • Regulates the CO2 intake
  • Help plants regulate and make better use of light and air (photosynthesis and respiration)
Flowering Stage
  • Encourages uptake of water
  • Essential for the development of flowers
  • Regulates the CO2 intake
  • Increases resistance to diseases
  • Help plants regulate and make better use of light and air (photosynthesis and respiration)
Organic Nitrogen, Potassium and Phosphorus nutrient mixes

What Is Potassium Deficiency?

As the name indicates this deficiency is the plant showing that it doesn’t have enough Potassium in her system to successfully move nutrients around.
Meaning that you may have all the nutrients you need in your soil for her, she won’t be able to pass it from the roots to the upper levels well, creating issues.

How to spot Potassium Deficiency on Cannabis?

As most ways of spotting deficiencies with Cannabis the symptoms show on the leaves.
The most recognizable sign are brown spots appearing and spreading on the leaves. Let’s get into it.

What are the signs of Potassium deficiency?

Potassium deficiency in pretty simple to diagnose.
The signs are pretty straight forward and aren’t very similar to other deficiencies, making it easier to diagnose correctly.
Here’s the steps of evolution of this deficiency:

  • Brown spots start to appear on the leaves.
    Generally this occurs towards the center of the leaf.
  • The Brown spots spread on the leaf.
  • The leaf starts to turn yellow
  • Generally starting at the tips, the leaves will curl up.
  • By the end, the leaf will be brown, curled up and dead

Now, here’s the evolution in image, as always you can click on the picture in order to see the full view.

Evolution of Potassium Deficiency

First brown spots starting to show up in the middle of the leaf

Early Signs – Brown spots appearing on the leaf

Brown spots spreading from the center of the leaf outwards

Brown spots spreading on the leaf

Brown and yellow spreading on the leaf

Leaf starting to turn yellow and brown

Potassium deficiency totally killed the leaf

Leaf is basically dead (the brown sections will keep on spreading)

How to solve Potassium Deficiency on Weed?

As with most nutrient deficiencies the best fix is to gradually increase the levels of nutrients given to the plant.
It’s important not to spike up the levels too harshly right away, you don’t want to be giving her too much nutrients and get her into a Nutrient Burn situation.
This is why we say increase gradually and observe how your plant reacts in order to find her sweet spot.

To sum up:

  • When a plant has Potassium deficiency she cannot transfer nutrients from the roots to the upper levels of the plant.
  • Increase the levels of Potassium provided in you watering mix in order to solve the problem.
    You should do this gradually in order to find the right levels needed and avoid Nutrient Burn.
  • Leaves that have been affected will not recover.
  • Keep an eye on the spreading of the symptoms in order to see if you solved the deficiency or not.

Most Common Reasons for P Defiency

The source of Potassium Deficiency are pH issues. The roots will absorb Potassium if the pH is above 6.2, so make sure your water is above that.
If this is the case and the plant is still showing signs of deficiency then you simply don’t have enough in your watering mix; Increase the amounts and you should see the spreading stop within the next couple days.

That’s it for this one folks.
Until next time, be safe and grow easy!

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