potassiumPotassium (K) is also one of those main elements that any cannabis plant needs.

It is the main element because cannabis plants require a large amount of potassium and it is only surpassed by Nitrogen in the quantities required by a cannabis plant.

Autoflowering plants take up Potassium in its iron form (K+) but in fertilizers this elements is usually in the K20 form.

Cannabis plants use potassium for a variety of different processes and functions and you need to supply an adequate amount of Potassium throughout the entire plant’s life cycle.

  • Potassium is directly linked to the cannabis plant’s resistance to pests and diseases.
  • It also plays a big role in the photosynthesis function as well as stomata development control and carbohydrate, sugar, starch movement, and production.
  • Potassium is found in the entire cannabis plant so it is responsible not only for green growth but also helps vigorous root development and it is also associated with all the processes that have anything to do with water transplantation and intake.

Potassium amount in different growth stages


In this delicate stage of autoflower plants growth you need to be very careful with the amount of fertilizer you use and it almost doesn’t matter if your N-P-K is 10-10-10 or 10-5-7 because you will be supplying the plant with 1/8 or 1/6 of the amount that is recommended.

Better stay safe with all-around fertilizer than induce some deficiencies of toxicities.

Potassium, as I mentioned before, is necessary for root growth and photosynthesis so you need to supply your cannabis plants with a fair amount of it. It is best to use a vegetative fertilizer (N-P-K 20-10-10 or anything close to that ratio) for the early and pre-flowering stages of the autoflowering plant’s life but be very gentle and don’t overdo anything.

A good rule of thumb is to start giving autos fertilizer only after two to three weeks of seedling, vegetative growth.


At this stage of growth you need to use the same fertilizer you used for the early stage but just start slowly increasing the dose.

Cannabis needs all of the macronutrients throughout its life but at the pre-flowering phase it needs Nitrogen the most, then comes Potassium which is closely followed by phosphorus.

When you reach the ½ amount of fertilized that is recommended then stop and stay at that mark because autoflowers don’t like too nutritious soil.


At the flowering stage, you need to use a fertilizer that has less Nitrogen and more Potassium and phosphorus.

Potassium is responsible for a healthy plant and if a plant is healthy it will produce big flowers and bigger amounts of THC giving you stronger smoke.

A good practice for flowering phase is to use a fertilizer with N-P-K ratios of something like (5-15-15) or anything close to that. When you change your fertilizer from vegetative to bloom (flowering) then you need to start slow again (1/6 or ¼ of the recommended dose) and rise the nutrient dose slowly not damaging the fragile autoflowering plant.

Potassium in chemical fertilizers

Potassium in chemical fertilizers usually is in the form of KCL (Potassium chloride) and if the label says that this fertilizer has 25% potassium the real amount of potassium that you get from that it is about 16% because potassium chloride is only 55 to 65% pure Potassium.

Potassium in organic materials

Organic Potassium is not hard to get and the most common material is ashes.

Plant ashes have in some cases up to 3% potassium, whereas wood ashes have about 2 to 5% potassium. These plant ashes if concentrated enough and separated from other materials are called potash, because it has about 80% potassium content!

You can get potassium from animal manure as it usually has about 2% potassium and seaweeds also have 2% to 3 % potassium content.

Potassium deficiency

Potassium deficiency usually is hard to diagnose and new growers usually confuse potassium deficiency symptoms with other nutrient deficiencies or other plant illnesses, stresses.

At first, Potassium starved autoflower plants appear to be normal and don’t give any clue that they are starving from potassium.

When the deficiency progresses autoflowering plants starts developing much more side branching than it usually does, so if your plant has countless side branches and they appear to be weak then maybe you have a potassium deficiency. If the deficiency is not treated it spreads rapidly and will start affecting older and newer leaves.

Cannabis needs potassium for heat control and water evaporation (potassium controls stomata opening and closing) so when it is deprived of potassium the inner temperature rises, because the stomata can’t open as often as it needs. When the inner temperature rises leaf tips (were the most evaporation happens) start to curl up because plant tries to lower the temperature.

If the inner temperature is not lowered then protein cells start to degrade and plant suffers from heat stress. So be on the lookout for a curled leaf tips in a normal growing temperature.

When deficiency progresses even more those curled dead tips start to change the color to brown and eventually necrotic (black). Usually, the color transformation happens from the edges of leaves and progresses inward in the veins

Potassium deficiency can be treated by changing the fertilizer to one where potassium is found in larger quantities.

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Potassium toxicity

Potassium overdose happens when the surrounding growing medium has too much potassium in it and it can cause some serious problems to your autoflower growth.

First of all, the plant will be stunned and the development of the roots will be slow. When Potassium is in a toxic amount other elements like Mg, Mn, Zn, Fe and even Ca will not be absorbed and you will see those deficiencies.

True Potassium overdose is hard to diagnose but if you see any of those other element deficiencies it might be potassium that is causing them to be locked out!

You can treat potassium toxicity as any other element overdose by flushing autoflower plants!


    • I haven’t used it myself, but have heard that it is quite good, because it has all the main plant growing chemicals and for the first 24 hours it is almost completely sterile. But be careful not to use older than a day or two urine as it will breakdown and release ammonia and other harmful chemicals that plants don’t like!

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