Gardening Plant Problems Garden Pests

What Is Insecticidal Soap? How to Make Your Own

Keep your favorite plants pest-free with simple ingredients

Person spraying insecticidal soap onto a rose bush

The Spruce / Jayme Burrows

Insecticidal soap is a mixture of water and the potassium salts of fatty acids and is commonly used to curb infestations of insects on indoor and outdoor plants. Soap sprays are effective for soft-bodied insects such as mealybugs and aphids. Insecticidal soap typically does not harm plants.

Soap sprays are some of the oldest insecticides used by gardeners in the old days; gardeners used to boil water with Fels-Naptha soap to create an effective soap insecticide. Over time, these "old-fashioned" remedies fell out of favor as they were replaced by much stronger and more toxic chemicals. Today, however, as the interest in organic and less chemical-intensive gardening continues to grow, insecticidal soap sprays have made a major comeback. There are some effective commercial products on the market labeled insecticidal soap, many including supplemental ingredients. But if you have the right ingredients, you can make your own.

How Do Insecticidal Soaps Work?

Insecticidal soap works through several mechanisms. The soap itself penetrates insects' cuticles, which causes cell collapse and desiccation. In other words, the spray eats away at the bug's exoskeleton, dries them out, and results in dehydration and death. The sprays also operate by suffocating insects such as scale.

How to Use Soap Sprays

Although soap sprays are less toxic to gardeners and non-pest animals, they can still be potentially damaging to some plants, especially if an oil has been added to the spray. Before the widespread use of any spray, test it on a small section of the plant first and wait at least 24 hours to see if there are any negative effects. Look for signs like spotting, wrinkling, and browning on leaves. If you see any negative signs, discontinue use of the product. Plants that are susceptible to damage from soap sprays include beans, cucumbers, ferns, gardenias, and peas.

When making a home DIY insecticidal soap spray, be careful of what ingredients you choose because there is a difference between detergents and soaps. Clear dishwashing detergents are not the same as soaps and should not be used in insecticidal soap sprays. Dishwashing liquid soap does not contain fatty acids and can also harm plants. Instead, use pure liquid castile soap. Do not use any product with fragrance, moisturizer, or other additives.

Warning

There is conflicting information about using certain liquid dish detergents to make DIY insecticidal soaps. These products are designed to strip grease and oil from surfaces and may harm beneficial pests while also severely drying out plants.

How to Make DIY Insecticidal Soap

You can make insecticidal soap with or without oil. There is some debate about whether or not you should use oil to enhance the effectiveness of your spray. Technically, oil is not necessary for the soap to work. However, adding oil will enhance the effectiveness of your spray and increase its shelf-life.

To make your insecticidal soap spray without oil, take these steps:

  1. Use a clean spray bottle for your mixture.
  2. Start with the weakest solution possible, mixing between 1 teaspoon and 3 or 4 tablespoons of soap per gallon of water and using it immediately.
  3. When you spray, soak both the tops and bottom of leaves and directly spray any visible insects. The spray needs to make direct contact with the pest insect to be effective.
Starting by using a clean, unused spray bottle

The Spruce / Jayme Burrows

Mixing together the insecticidal soap in a bowl

The Spruce / Jayme Burrows

Spraying insecticidal spray onto an infected rose bush

The Spruce / Jayme Burrows

To make an insecticidal soap spray base with oil, take these steps:

  1. Use a clean jar with an airtight lid.
  2. To make an easy at-home spray base with oil, mix 1 tablespoon of soap with 1 cup of cooking oil and emulsify by shaking the jar vigorously.
  3. When it comes time to spray, mix 1 to 2 1/2 teaspoons of this base to every 1 cup of water in a clean spray bottle and spray immediately.

Tip

Soap sprays can also be enhanced with additives to control fungus and chewing insects. You can safely add bacullus thuringiensis (BT), copper fungicide, or pyrethrin to the mix, depending on your needs.

Closeup of clean glass jars

The Spruce / Jayme Burrows

Pouring the insecticidal soap mixture into a glass jar

The Spruce / Jayme Burrows

Pouring insecticidal soap concentrate into a spray bottle

The Spruce / Jayme Burrows

Types of Insects to Control With Insecticidal Soap

To varying degrees, soap sprays are effective against the following insects. But note that sprays are not effective on chewing insects such as caterpillars and beetles.

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Insecticidal Soaps. University of Connecticut.

  2. Managing Plant Pests With Soaps. University of Florida IFAS Extension.

  3. Soap Sprays as Insecticides. Agriculture and Natural Resources, University of California.

  4. Chiggers. Entomology at the University of Kentucky.