Neem Oil and Potassium Soap: How to Fight Pests and Diseases in Your Garden

Combate plagas y enfermedades con aceite de neem y jabón potásico

Translated by Nick R

When a pest or disease appears in our plants, we often think that all is lost or that it’ll be too hard to solve it. However, 2 magical products are very efficient in fighting these problems in your garden, and what’s best is that they are inexpensive and plant-friendly.

Therefore, this time we’ll talk about the properties of neem oil and potassium soap to know what their benefits are. We’ll also tell you how to prepare them, how often to apply them and where you can buy them.

What is neem oil? 

It’s a vegetable oil extracted from the neem tree (Azadirachta indica) seeds and flowers, which is native to India, but due to its popularity, its cultivation has spread worldwide.

It has rather a strong smell, often described as a combination of peanuts and garlic, although it’s that smell that actually scares insects away. In addition, it contains an element called Azadirachtin that works as a natural insecticide by stopping pests or diseases from feeding and growing.

The seed pressing to obtain the oil can be done using a cold or hot process. We recommend using the cold-pressed method as none of its properties are lost in this way.

That said, neem oil acts in 3 ways:

  • It stops the insect from feeding on the plant, i.e, the insect loses its appetite.
  • It prevents the pest from reproducing or the disease from spreading.
  • It kills the insect or, at minimum, repels them.

Therefore, this pesticide acts from inside the plants, and its objective is to kill the annoying insects feeding on the sap.

Benefits of neem oil 

It can fight hundreds of pests. It’s so effective that it can kill up to 200 species of insects. The most common ones include aphids, mealybugs, whiteflies, spider mites, and caterpillars. It can even eradicate nematodes which are tiny worms that are often undetected as they live in the soil and feed on the roots.

Neem controls insects at any growth stage. That is, it’s a product that attacks both eggs and larvae, as well as adult insects. Also, as mentioned above, it keeps pests from reproducing.

It’s an excellent fungicide and bactericide. Neem oil application on plants creates a protective layer against diseases. Moreover, it’s able to control and even wipe out fungi and bacteria such as rust, anthracnose, fumagine, fire blight, and many more.

It’s safe for plants and beneficial insects. Clearly, it’s an organic product, but it also biodegrades rapidly. Likewise, since its function is to kill plant-feeding insects, bees and other pollinators won’t be harmed.

It has a good quality/price ratio. Later on, we’ll explain what approximate amount to use; however, the amount used to fumigate the plants is minimal. As a result, this oil lasts for a long time. Also, we’ve already told you why it’s a top-quality product.

Pests don’t become immune to the oil. Sometimes it happens that insects form pesticide resistance, which causes them to stop working. The neem oil, on the other hand, continues to be effective after repeated applications. What makes it special is that it acts from the inside, so when the pest tries to feed on it, it’ll be feeding on poison, actually.

How is neem oil used? 

Neem oil is not applied directly to plants but mixed with water and soap.

Theoretically, any type of liquid soap can be used since its function is to dilute the oil in the water. However, the combination preferred by experts is neem oil with potassium soap, which we’ll talk about shortly, and later we’ll tell you the exact dosage to use.

Of course, it’s good to use protection so that the product doesn’t come into contact with your skin; it can cause irritation. Also, if you’re sensitive to odors, you better wear a mask or cover your nose when uncovering the soap to use it.

What is potassium soap? 

As its name suggests, it’s a soap composed of potassium salts that have been long used to control and prevent the most common pests. It’s also a 100% ecological product as it is free of toxic compounds and, therefore, doesn’t contaminate.

So, it would be great for plants that are suffering from aphid, whitefly, mealybug, red spider mite, etc. Although it also works as a disease prevention method.

Therefore, potassium soap works in the following ways:

  • It removes the remnants of honeydew that certain pests excrete when they feed on the plant’s sap.
  • It causes the insects to suffocate and die instantly.
  • The fungicidal properties of this product work when the plant is wet. That is, once the liquid dries, it’s no longer effective.

As we can see, this solution acts through external contact; that’s to say, the insect dies when it’s reached by the potassium soap.

Benefits of potassium soap 

Potassium soap is biodegradable and organic. When this product decomposes becomes potassium carbonate. Therefore, it turns into a fine fertilizer for your crops. So, it goes from a pesticide to a fertilizer.

Potassium soap bonuses the plants. Since the soap removes molasses, it helps keep the stems and leaves completely clean. In this way, the plant gets a break and continues growing more vigorously, free of that sticky substance.

Potassium soap has an excellent quality/price ratio. Like neem oil, it’ll last for a long since the amount used is little when diluted in water. So, investing in potassium soap is a spectacular idea to take care of your garden.

Potassium soap improves other products’ performance. Soap enhances the plant’s absorption of pesticides or fertilizers. Especially those with waxy water-repellent leaves, so they can absorb these products more easily.

How to use potassium soap? 

The exact dosage may vary by brand, but generally, you dilute between 10 and 20 milliliters of potassium soap per liter of water. The mixture should be sprayed over the entire plant, paying particular attention to the leaves’ backside, because that’s where the pests settle the most.

It’s advisable to apply it early in the morning or at dusk because, in intense sunlight, the product could burn the leaves. Also, you better avoid applying it on a rainy or windy day if the plants are outdoors.

Otherwise, the rain will wash the soap away, and the wind will dry it quickly.

We also recommend that the product doesn’t get in contact with the skin to avoid any possible irritation, especially on sensitive skin.

Ecological insecticide based on neem oil and potassium soap 

Now, we’ll show you how to mix these 2 products to create the most effective insecticide. Besides, you’ll learn where to find them.


You’ll need the following ingredients:

  • 5 milliliters cold-pressed neem oil.
  • 2 to 3 milliliters potassium soap
  • 1 liter water

All you have to do is mix all these components and put the liquid in a sprinkler or watering can, depending on the system you want to use. We recommend using a syringe to measure the quantities easily.

As you can see, although the product amount to use is diminute, its effectiveness is still the same. There is no need to oversaturate by applying extra oil or soap because that won’t make a difference.


Apply the product with a sprinkler, spraying only the leaves and stems, or include it in the irrigation water. The latter option helps the product to remain on the plant longer, is an excellent preventive method, and remember that it also becomes a fertilizer.

For combating pests or controlling disease the application frequency can be every 4 or 5 days for a few weeks until the ailment has disappeared. If you want to form a protective layer, every 15 days will be enough.

When spraying the insecticide to remove the pests that are attacking your garden, be sure to cover the stems and leaves thoroughly. Also, try to apply it the same day you prepare it so that it doesn’t lose its properties. The best thing is that, if you have enough of the preparation, you can use it on the nearby plants or on the whole crop to fertilize and protect it.

The best is to avoid using this kind of product that touches the leaves and stems directly, in high temperatures or during strong sunlight hours. That in order to prevent the risk of burning the plants.

It’s also preferable to spray your crops at least 15 days before harvest. This is to avoid any residue, especially of neem oil.

Final Recommendations 

You may be wondering if you can get a product on the market that already has combined neem oil and potassium soap: the answer is yes. However, it is not so widely offered or popular, as it usually incorporates other components that are believed to affect the properties of the 2 main components.

For that reason, every experienced gardener will tell you that it’s much better to invest in both products separately and prepare the mixture every time you need it and in the amount you require.

Although they may seem a bit expensive, these fungicides will last for years. That is because very few amounts are used, and thus you don’t need to apply the product extensively or over long periods for it to work.

We suggest you do your own research to find the products that most suit your quality requirements, budget, and your plant needs. Look for more info at local stores or online platforms such as Amazon or eBay. We’re sure you’ll find the best for you.   

In conclusion, as you can see, having neem oil and potassium soap in your gardening kit will get you out of lots of trouble with pests and will even help you fight diseases, which we both know are hard to deal with.

We hope, then, that this blog has been of great value for you to learn which organic and ecological insecticide you can implement in your garden, with the certainty that it'll be useful and pleasant for your plants.