What Is Insecticidal Soap? A Guide To Using Insecticidal Soap On Plants

Last Updated November 11, 2023 By Bella Zinti

Home » Plants » What Is Insecticidal Soap? A Guide To Using Insecticidal Soap On Plants

Whether you are a houseplant enthusiast, grow a vegetable garden, or have a landscape of beautiful outdoor plants, the time will come when you are faced with pests. These harmful insects can really do a number on plants! They can significantly reduce a fruit or vegetable harvest or even kill plants altogether. And once an infestation sets in, the battle can seem daunting.

Many gardeners used to choose a broad-spectrum pesticide to combat pests. However, they are increasingly looking at different options thanks to modern research. Too many chemicals from pesticides are making their way into our soil, water, and food. Additionally, beneficial insects are being killed alongside the harmful ones!

Insecticidal soaps are an effective solution to your pest problem! These homemade insecticidal soap sprays kill pests on contact using natural ingredients that do not harm the environment. And there's the added benefit that they are affordable and quick to make! Keep reading to learn more about insecticidal soaps - how to apply them, how to make them, and what downsides you should be aware of.

What Is Insecticidal Soap?

Insecticidal soap is an eco-friendly, natural pesticide employed for the management of a wide range of garden pests, with a primary focus on soft-bodied insects such as aphids, mealybugs, spider mites, and whiteflies. It is formulated by combining water with a mild soap or detergent and is designed to disrupt the protective outer layer of insects, ultimately leading to their demise.

Insecticidal soap is considered a safer alternative to synthetic chemical pesticides and is commonly used in organic gardening. It is generally considered safe for humans and pets when used as directed. It is less toxic than many synthetic chemical pesticides and does not leave harmful residues on plants or the environment. Insecticidal soap contains molecules with surfactant properties. Surfactants are compounds that reduce the surface tension of liquids, enabling the soap solution to uniformly coat the surfaces of both plants and pests.

Insecticidal soap, primarily known for its effectiveness against insect pests, is also valuable in combating plant fungal diseases. When diluted and applied to plant foliage, insecticidal soap disrupts the protective barriers of fungal spores and hyphae. This interference hinders fungal growth and prevents the spread of diseases like powdery mildew, black spots, and rust. Unlike synthetic chemical fungicides, insecticidal soap is gentle on the environment and poses minimal risk to good insects. Its versatility in targeting pests and some fungal pathogens makes it a valuable addition to organic gardening practices, promoting healthier plants and reducing disease pressures.

Why Use Insecticidal Soap Over Conventional Insecticides?

Using insecticidal soap instead of conventional insecticides offers several compelling reasons for both gardeners and environmentally conscious individuals. Insecticidal soap is biodegradable, has low toxicity, and presents minimal risks to humans, pets, and beneficial insects. Its primary focus is on soft-bodied pests, minimizing the chances of causing harm to non-target organisms. Moreover, it has a shorter residual effect, decreasing environmental contamination. It is a superb option for edible plants, guaranteeing the safety of homegrown produce. Additionally, insecticidal soap is less likely to lead to pesticide resistance, making it a sustainable and effective solution for pest management.

Conventional insecticides, on the other hand, often contain toxic chemicals that can persist in the environment, contaminating soil, water, and air. These substances harm non-target organisms like bees, birds, and aquatic life, disrupting ecosystems. Not to mention, these toxic substances can pose risks to human health and contaminate the food chain.

How Is Insecticidal Soap Different From Dish Soap?

Insecticidal and dish soap may appear similar, but they fulfill different roles. The primary distinction is that dish soap is not a genuine soap solution. Instead, they are detergents. Detergents are designed to strip grease. Using liquid dish soap to make DIY insecticidal soaps can damage plant surfaces by stripping away the waxy cuticle on the leaves and causing the plant to lose water rapidly. Certain plants are more prone to this damage than others, with susceptible plants such as succulents being most harmed by dish soap. In addition, dish soup can also be toxic to beneficial insects.

Insecticidal soap, on the other hand, is formulated to target garden pests, featuring a carefully balanced pH level that won't harm plants. It also lacks additives like fragrances and chemicals found in dish soaps. Insecticidal soap's surfactant properties break down insects' protective coatings, aiding in pest control without harming beneficial insects or plants.

How is Insecticidal soap Different From Horticultural Oil?

Insecticidal soap is primarily composed of mild liquid soap (e.g., castile soap, dish soap, or hand soap) mixed with water. It primarily works by disrupting soft-bodied insects' cell membranes and outer protective coatings, causing them to dehydrate and ultimately die. 

Horticultural oil, often called dormant oil or summer oil, is made from highly refined mineral oil or vegetable oil. Horticultural oil works by smothering and suffocating pests and their eggs. It forms a physical barrier over pests, blocking their spiracles (breathing tubes) and causing them to die from lack of oxygen. It's effective against a broader range of pests, including soft-bodied and hard-shelled insects and some mites.

How Does Insecticidal Soap Work?

Insects have a waxy, waterproof layer on their exoskeleton called the cuticle. This cuticle helps them retain moisture and protect themselves from the environment. Insecticidal soaps work upon direct contact with soft-bodied insects. When insecticidal soap comes into contact with the insect, it breaks down the cuticle's waxy layer. Potassium salts of fatty acids disrupt insects' cell membranes, leading to structural breakdown and increased permeability. The contents of the cells spill out, causing each cell to die and the insect to suffocate. Because of how insecticidal soap works, they can kill soft-bodied pests in both their larva and adult stage.

The specific insects that it is effective against include:

  • aphids

  • whiteflies

  • spider mites

  • mealybugs

  • azalea lace bug nymphs

  • earwigs

  • leafhoppers

  • thrips

  • plant bugs

  • Sawflies

  • Psyllids

  • Leafhoppers

  • Caterpillars

  • Scale insects

  • scale insects

  • sawfly larvae

  • squash bugs

What Are the Advantages Of Using Insecticidal Soap

Environmentally Friendly: Insecticidal soap's biodegradable nature ensures it breaks down rapidly in the environment, reducing the risk of soil and water contamination. This makes it a sustainable choice for gardeners who prioritize eco-conscious practices and aim to reduce their environmental impact.

Selective Pest Control: Insecticidal soap's ability to target soft-bodied pests while sparing the good insects is a crucial advantage. It allows natural predators like ladybugs and lacewings to thrive, creating a more balanced and healthy garden ecosystem.

Safe for Edible Plants: One of the most significant advantages is that insecticidal soap is safe for edible crops. This means you can effectively protect your fruits and vegetables from pests without worrying about chemical residues that might affect their safety for consumption.

Low Toxicity to Humans and Pets: When used correctly, insecticidal soap poses minimal risks to human health and pets. It is virtually non-toxic to animals and birds. Unlike some chemical pesticides, it doesn't release toxic fumes or leave harmful residues that could be ingested or inhaled, providing peace of mind for gardeners with families and pets.

No Residue Buildup: Insecticidal soap's shorter residual effect means there's less risk of chemical buildup in the soil and water over time. This encourages the long-term well-being of the soil and fosters a safer and more sustainable gardening environment.

Effective Against Multiple Life Stages: Insecticidal soap doesn't discriminate between pest life stages. It can target eggs, nymphs, and adult insects, ensuring comprehensive pest control throughout an infestation's life cycle.

Reduced Risk of Resistance: The physical action of insecticidal soap reduces the likelihood of pests developing resistance. This makes it a more dependable and sustainable long-term solution for pest control.

Ease of Use: Insecticidal soap is simple to mix and apply. It doesn't require specialized equipment or protective gear, making it accessible for gardeners of all experience levels. Its user-friendly nature makes it a convenient option for swift and efficient pest management.

Immediate Action: Insecticidal soap works on contact, providing swift results. When you notice a pest infestation, you can take action promptly, preventing further damage to your plants.

Effective Fungal Disease Treatment: Insecticidal soap can also be used to combat certain fungal diseases like powdery mildew, black spots, and rust. When applied to affected plant foliage, it disrupts the protective barriers of fungal spores and hyphae. This interference inhibits fungal growth and fungal growth and mitigates the further spread of diseases.

What Are Downside To Insecticidal Soap

Selective Pest Control: Insecticidal soaps primarily target soft-bodied pests like aphids, mealybugs, and spider mites. While this selectivity is an advantage, it also means that it may not be effective against hard-shelled insects like beetles, weevils, or caterpillars. You may need alternative treatments for these pests.

Limited Residual Effect: Insecticidal soaps have a relatively short residual effect. It works on contact but doesn't provide long-term protection. Any pests that were not thoroughly sprayed with the insecticidal soap spray will not be affected by that application. This means you may need to reapply it more frequently, especially after rainfall or as new pests emerge.

Does Not Get Rid Of Eggs: Insecticidal soap primarily targets soft-bodied insects' active, crawling, or feeding stages. While it can effectively eliminate adult insects and nymphs (young insects), it may not always effectively eliminate insect eggs.

Potential Plant Sensitivity: Certain plant species or cultivars may exhibit varying sensitivity to insecticidal soap. Before applying it broadly, it's advisable to test it on a small section of your plants to ensure they don't show signs of leaf burning or other adverse reactions. Here is a list of particularly sensitive plants:

  • Japanese maple

  • sweet peas

  • horse chestnut

  • mountain ash

  • easter lilies

  • Ferns

  • Bleeding Heart

  • Gardenia, Jade

  • Lantana Sweet Peas

  • Crown of Thorns

  • Nasturtium

  • Easter Lily

  • Cherry Hawthorn

How To Make Homemade Insecticidal Soap

Many recipes for DIY insecticidal soap spray are available, and their effectiveness depends greatly on whether detergent or true soap is used. Below is a DIY insecticidal soap recipe that is proven to be both safe and effective.


1 tablespoon of mild liquid soap (e.g., castile soap, dish soap, or a gentle hand soap)

1 quart (4 cups) of water

A spray bottle

Optional: 1 teaspoon of neem oil or a few drops of essential oils like peppermint, rosemary, or garlic oil (for added repellent properties)


  1. Choose a mild, pure liquid soap that doesn't contain harsh chemicals or added fragrances. Suitable pure liquid soap options include castile soap, dish soap, or gentle hand soap.

  2. Measure one tablespoon of the chosen soap and place it in a quart-sized container, such as a mixing bowl or jug.

  3. Pour four cups (1 quart) of water into the container with the soap. Use room-temperature water.

  4. If you want to enhance the repellent properties of your DIY insecticidal soap, add one teaspoon of neem oil or a few drops of essential oils like peppermint, rosemary, or garlic oil. These oils can help deter pests.

  5. Stir or shake the container gently to ensure the soap and optional ingredients are fully dissolved in the water.

  6. Use a funnel to pour the DIY insecticidal soap mixture into a clean and empty spray bottle. Label the bottle clearly to identify its contents.

  7. Before applying the homemade solution to your plants, perform a patch test on a small area of one plant to ensure it doesn't cause any adverse reactions.

Tips For Using Insecticidal Soap Spray

Know your pest: Clearly identify the pests you're targeting. Insecticidal soaps are most effective against soft-bodied insects.

Avoid Using it on hot or sunny days: Insecticidal soaps are also frequently phototoxic. Avoid spraying on bright sunny days or days when the temperature will be hot ((90° F or above), as the soap will quickly cause plant damage. Spray only into the early morning or early evening.

Avoid Using it in humid conditions: You should avoid using insecticidal soap spray when relative humidity is 90% and above, as it can be less effective and harm the plants. Elevated humidity levels can impede the drying process of the soap spray on plant leaves. Insecticidal soap relies on drying out and suffocating pests on contact. When the air is saturated with moisture, the soap may take longer to dry, reducing its effectiveness in killing or deterring pests.

Perform a Patch Test: Before applying the solution to your entire plant, conduct a test on a small, inconspicuous area to assess any potential adverse reactions. Allow 24 hours to observe the plant's response.

Plant Condition: Avoid treating plants experiencing moisture or drought stress, as insecticidal soaps may cause leaf burn in such conditions.

Reapply as Needed: Monitor your plants regularly for signs of pest infestations and reapply the insecticidal soap as necessary. After rain or irrigation, consider reapplying, as these events can wash away the soap.

Be Thorough but Not Excessive: Coat the plant surfaces thoroughly with the soap spray, but avoid saturating the plants. Overly wet leaves can cause stress and increase the risk of fungal issues.

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About the author

Bella has a Bachelors degree in interior design, is a master gardener. She designs nourishing outdoor & indoor spaces guided by the practice of Feng Shui.