Potassium Soap: What is it? What ingredients does it have? How do we prepare it?

Potassium soap (also known as potash or potassium soap) is an excellent organic remedy against pests, since its soapy action attacks the cell membranes of the external tissues of insects, affecting their external permeability and influencing their life cycle.

It is also a great cleaning agent, which we can use, when diluted in water, to clean plants.

It is non-toxic, so it does not contaminate or cause problems for people and animals.

What is potassium soap?

Potassium soap is composed of three main elements:water, lipids and potassium hydroxide.

When the lipids come into contact with potassium hydroxide, a chemical reaction takes place, obtaining a water-soluble glycerin. This mixture has an alkaline pH and does not affect plant tissues.

In addition, it degrades quickly, so it does not require security periods to harvest the fruits.

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What is potassium soap made of?

Potassium soap consists of three main elements: water, fats and potassium hydroxide.

When fats meet potassium hydroxide, a chemical reaction takes place, the result is mixed with water and liquid potassium soap is obtained. The resulting mixture does not affect plant tissues and its rapid degradation makes it become a fertilizer for plants.

How can potassium soap be useful in your garden?

potassium soapis an excellent insecticide: it is ecological, it does not attack beneficial insects, such as bees, and it can also be reused as fertilizer, because when it decomposes it releases potash carbonate, which the roots can absorb.

It is also not harmful to pets or humans.

Potassium soap can also serve to prevent the appearance of fungi.

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When should we use it?

We can use them at any time, although it is advisable to apply potassium soap at dawn or dusk.

In addition, we must bear in mind that there is not too much sun because, by spraying the plant, it could burn the leaves. In the same way, we will have to be careful not to apply it on a rainy or windy day, since otherwise the rain will wash the application, or the wind will dry it, and the effort will not have been worth it.

How should potassium soap be applied?

Potassium soap acts by direct contact. As soon as an insect lands on the substance, its minutes are numbered.

For this reason, it is essential to apply the product along the most tender areas of the plant, since they are usually the main access areas for most pests.

The correct dose will depend on several factors, mainly the type of plant and the severity of the pest.

In general terms, it is advisable to dilute a quantity of potassium soap in a proportion of 1 or 2%, or what is the same, about 10 or 20 ml of soap per liter of water.

The application system will be by spraying, making sure to cover both the beam and the underside. Preferably, do it very early in the morning, or in the evening, when the sun’s rays are not so intense, since the high temperatures cause the soap to burn the plants.

The treatment will work immediately, but sometimes the application must be repeated. For this, it is recommended to apply potassium soap every 15 days, within a period of 3 or 4 months.

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What dose is correct when applying potassium soap?

Depending on the type of potassium soap, the dosage to use will vary.

Potassium soap is generally used in a proportion of 1 or 2% diluted in water, that is, about 10 to 20 ml of soap per liter of water.

In any case, being a vegetable, organic and harmless product, nothing will happen if at any time we exceed the dose.

This is something that we must take into account when using chemical pesticides that, in addition to negatively affecting the environment and ourselves, can also kill the plant in a sudden way.

How to prepare potassium soap?


  • 1 liter of water.
  • 4kg of wood.
  • Lemon juice.
  • 1 liter of olive oil.
  • 1 potato.


  • metal pot
  • Packaging containers.
  • Metal stirrer.
  • Instrument to measure pH.

Procedure for making potassium soap

  1. Burn the wood and wait for it to be completely consumed.
  2. Collect the ash and put it in the metal pot, later adding a liter of water. Shake until a homogeneous mixture is obtained.
  3. Let stand for 3 days.
  4. After that period, place the potato in the mixture. This will help us determine if the potassium carbonate concentration is valid. If the potato floats, it means that the concentration is acceptable. Otherwise, the process will have to be repeated, this time with a little more ash.
  5. If the concentration is good, add 1 liter of olive oil and stir until a homogeneous mixture is achieved. The texture should be thick and thick. This glycerin is already considered potassium soap.
  6. Now, we need to measure the pH of the mixture. For this, you can use a pH test strip. If the pH is between 8.0 or 9.0, it means that the result is alkaline, so you must add 5 drops of lemon to reduce the values.
  7. To apply, you only have to dilute in water, according to your specific needs.

What pests can we fight with it?

It works to eliminate soft-bodied insects and arthropods, such as mites, aphids, whitefly, mealybug, ribbed mealybug, thrips, among others.

It is also useful for removing caterpillars, leafminers, and grasshoppers, but these insects, due to their size, can be more difficult to control with this method alone.

As for pollinating insects, such as ladybugs, bees, bumblebees and hoverflies, they are not affected.

There are different ways in which potassium soap acts to eliminate insects:

  • Entering through the insect’s trachea, which causes an alteration of its cell membranes.
  • Soap can dissolve and attacks the cell membranes of external tissues, as well as the wax layer in the cuticle of insects, affecting their external permeability and influencing their life cycle.
  • It can also block the trachea or any other form of respiration, leading to suffocation of the insect.
  • Finally, it can interfere with growth hormones or affect the metabolism of insects.

Main advantages of potassium soap

Effective insecticide and repellent:Potassium soap can be used to prevent pests, how to combat them once they have manifested.

Cleaning agent: Diluted in water, it helps to clean the plants. It can be an excellent remedy to combat dust in our crops.

It integrates very well with other remedies, such as insecticides, fertilizers or fungicides, as long as they have a pH above 10. This ensures that we do not have any compatibility problems.

Potassium soap can be used at any stage of plant growth, it is even valid to apply at the beginning of the transition of the flowering stage.

Despite its cost, it is a fairly profitable solution, offering an excellent cost-benefit ratio.

Where to buy potassium soap?

We buy our bottles directly from Amazon (here) and it gives us good results.

However, it can be purchased at any specialty store.

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