Plant Being Sprayed With Homemade Soap Spray
(Image credit: Leisan Rakhimova)

Today everyone wants to reduce their carbon footprint, live sustainably, and help take care of the environment. Gardeners are no different. Many of us are on the lookout for organic, non-toxic pest control. Homemade insecticidal soap is a great place to start.

Sure, you can always buy commercial insecticidal soap spray, but it's cheaper and really easy to make your own. Interested in safely removing pests from your garden? Read on to learn what insecticidal soap is, how it works, and how you can make your own at home.

What is Insecticidal Soap?

Insecticidal soap -- also known as horticultural soap -- is a non-toxic, environmentally healthy treatment for some types of soft bodied pests such as aphids, whiteflies, spider mites, and mealybugs. It can also help eliminate sooty mold, honeydew, and other leaf fungi.

Soap is made from the activity of an alkali substance like sodium or potassium hydroxide on fat. Soap is the general term for these salts of fatty acids which are then mixed with whale, fish, coconut, corn, veggie, soybean or linseed oil.

Typically insecticidal soaps contain potassium salts of fatty acids naturally found in fats and animal oils or plant derived oils. This means that insecticidal soaps differ from their more toxic counterparts -- modern soaps use potassium hydroxide, a traditional lye.

How Does Insecticidal Soap Work?

When insecticidal soap is sprayed onto a plant’s foliage, it comes into contact with the pest and kills it. Insecticidal soaps disrupt the cell membranes of soft-bodied insects, resulting in suffocation. To be most effective, insecticidal soaps must be applied vigilantly and thoroughly, and may need to be reapplied weekly until you attain the desired result.

Is Insecticidal Soap the Same as Dish Soap?

There are many sources that say insecticidal soap can be made from liquid dish soap at home. While the resulting DIY insecticidal soap may work, it very much depends on the type of dish soap you have.

Dish soaps are not true soaps, but rather detergents, which are made of synthetically produced chemicals made specifically to strip grease and oil from cookware.

Using detergent-based soap as insecticidal DIY soaps may remove the waxy layer from the surface of the foliage, opening it up to microbial, viral and fungal disease. The loss of this waxy cuticle also causes the plant to lose more water, effectively drying the plant out. Some plants with a thick waxy layer, such as succulents, are more susceptible than others.

DIY insecticidal soaps made from detergents can also affect beneficial insects, so while they clean dirty cutlery well, they are not organic and not suited for use in an organic gardening approach. Check the label of your dish soap to read the entire list of contents, or contact the company before using it as an insecticide.

How to Make Natural Insecticidal Soap

You can find many recipes for DIY insecticidal soap on the internet. Some work and some don’t. It really depends on whether you use detergent or pure soap. Many recipes call for the use of dish soap, which has many down sides, although some varieties work on specific pests.

Traditional Homemade Insecticidal Soap

Here's an environmentally friendly and proven DIY insecticidal soap. Mix together and pour into a spray bottle:

  • 2.5 tablespoons (37 ml) vegetable oil
  • 2.5 tablespoons (37 ml) pure liquid soap (not detergent)
  • 1 gallon (3.8 L) warm water (distilled or tap, but not hard)

Pest Repellent Insecticidal Soap

Mix together and pour into a spray bottle:

  • 1 tablespoon (15 ml) pure liquid soap (not detergent)
  • 1 quart (1 L) warm water (distilled or tap, but not hard)
  • 1 teaspoon (5 ml) ground red pepper or garlic
  • 1 teaspoon (5 ml) apple cider vinegar

Precautions for Using Insecticidal Soaps

There are few limitations to insecticidal soaps. Just be sure to thoroughly wet the insects, and be aware that effectiveness may be limited if the soap solution dries or washes away. Phytotoxicity may occur if applied during hot days, so avoid spraying if temperatures are over 90 F (32 C).

Even organic insecticidal soaps can harm beneficial insects or plants that are phototoxic. They are generally safe for humans and animals. However, some people can get a rash from them, so it's best to wear gloves when applying.

Since there is no residual activity left behind by insecticidal soaps, they rely on contact to kill pests. If an insect has not come into contact with the spray, it isn't affected. Also insecticidal soaps have no efficacy on insect eggs.

For example, insecticidal soaps work on azalea lace bug nymphs but not their eggs. Further, all stages of the lace bug live on the underside of the leaf, which is often not thoroughly sprayed with insecticidal soap.

BEFORE USING ANY HOMEMADE MIX: It should be noted that any time you use a home mix, you should always test it out on a small portion of the plant first to make sure that it will not harm the plant. Also, avoid using any bleach-based soaps or detergents on plants, since this can be harmful to them. It is important that a home mixture never be applied to any plant on a hot or brightly sunny day, as this will quickly lead to the burning of the plant and its ultimate demise.

Amy Grant

Amy Grant has been gardening for 30 years and writing for 15. A professional chef and caterer, Amy's area of expertise is culinary gardening.