How to Use Potassium Soap for Plants

By Mary Smith. July 22, 2021
How to Use Potassium Soap for Plants

Potassium soap is a special type of soap which has two functions. Firstly, as a soap, it is used to clean. Secondly, it is an insecticidal agent. This means it has the power to kill insects. This makes it very useful for plants. It can kill aphids and other pests, but it does not contain chemicals which will be harmful for plants. You can purchase other insecticides, but many can cause damage to the plant or plants around it.

At oneHOWTO, we show you how to use potassium soap for plants. Specifically, we look at how you can clean the plant using this soap and kill aphids by using it as an insecticide.

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What is potassium soap used for?

Potassium soap (also called potash soap) is a natural pesticide for plants. The reason why potassium soap is so good for plants is due to the following properties:

  • It is a natural product it is a product that is composed of fats (or lipids), potassium hydroxide and water. This composition is non-toxic, something which can be difficult to find in commercial soaps.
  • Pest control: its natural composition gives it enough capacity to kill the aphid, which dies from suffocation. However, it is true that it is most effective when used early in the insect infestation.
  • Eliminates honeydew residue: potassium soap also has the peculiarity that it can kill both this pest, as well as the honeydew residue which aphids produce and leave on plants. This helps prevent future infestations.
  • Provides potassium to plants: apart from the insecticidal properties against aphids, potassium soap has a number of other advantages, such as providing potassium to plants.

If aphids aren't your problem, it is possible you are dealing with a different pest problem. If so, our article on how to get rid of ants naturally might be of help to you.

How to Use Potassium Soap for Plants - What is potassium soap used for?

Preparation of potassium soap as an insecticide

In many gardening stores and nurseries they sell products to kill aphids. Among them is potassium soap, although it can also be prepared at home. Instead of applying potash to your plants directly, it is best to prepare it so you can increase its effectiveness. This means you should use it with other ingredients and apply it in a specific way. Fortunately, we have both to show you how it's done:


  • A tablespoon of potassium soap
  • A tablespoon of vinegar
  • One tablespoon of 96-proof alcohol
  • A liter of water


The method of application is very simple and you just have to follow this series of steps, which are easy and fast:

  1. Warm the water and place in your container (the heat helps to dilute the soap).
  2. Add the spoonful of soap and stir.
  3. Then, pour in the mixture the tablespoon of vinegar and the 96-proof alcohol.
  4. Mix well again so that the result is homogeneous.
  5. Let it rest for an hour to cool.

After this time, it can be poured into a bottle. It is best to use a spray diffuser bottle so you can apply it all over the plant more easily.

If you have other pest problems with you indoor or outdoor plants, we have related articles to help. Check out our guides to getting rid of spider mites on plants and how to get rid of mealybugs on outdoor plants.

How to use potassium soap on plants

When talking about how to use potassium soap for plants, we should know they are both used to clean the plant and to get rid of aphids. Firstly, check out our article on how to clean the leaves of plants to learn the basics. However, you can use potassium soap on plants which don't have an aphid infestation, as long as you do so minimally. Here is how to clean a plant with potassium soap:

  • The best time to apply potassium soap on plants with aphids is at sunrise or sunset.
  • It is important to choose days that are not windy so that the product remains on the plant as long as possible (if you are applying to outdoor plants).
  • You should never apply potassium soap to kill aphids on rainy days because the rain will remove the product from the plant and, consequently, the insects will remain.
  • Spraying is the best way to apply the product, focusing especially on the areas with the highest concentration of aphids and putting the potassium soap directly on them.
  • It is essential not to over-moisten the plant with potassium soap, even if there is a lot of aphids. The pest infestation does not end at once and, by putting more product, the aphid will not die sooner.
  • It is important to check the entire plant well, paying special attention to the back of the leaves and the areas that are more hidden.

Applications should be carried out approximately every five days, repeating the entire process until all the insects have been killed or moved on.

Getting rid of aphids on plants with potassium soap is a great natural way to eliminate this pest. However, it is not the only option available to you. We have a helpful article on how to get rid of aphid naturally if you don't have access to potassium soap.

If you want to read similar articles to How to Use Potassium Soap for Plants, we recommend you visit our Gardening & plants category.

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