What Is Horticultural Soap: Information On Homemade Soap Spray For Plants

By Amy Grant

Taking care of pests in the garden doesn’t need to be expensive or toxic. Horticultural sprays are a great way to combat many issue in the garden without harming the environment or your pocketbook. Learning how to make insecticidal soap spray for plants is easy to do and the benefits are worth the extra effort.

What is Horticultural Soap?

What is horticultural soap? Horticultural soap is not a cleaning product for foliage, it is an environmentally friendly application used to eliminate small soft bodied insects such as aphids, whiteflies, spider mites and mealybugs.

Horticultural soaps may be used either on indoor houseplants or on outdoor plants, including vegetables. Insecticidal soaps have several advantages over pesticides in that they leave no nasty residue, are natural and, therefore, non-toxic to animals and birds and do not harm beneficial insects. They are often also less expensive solutions to pest problems.

Horticultural soaps are derived from petroleum or often plant oils. When horticultural soap is sprayed onto the plants’ foliage, it comes into contact with the pest and kills it. Horticultural soaps disrupt the cell membranes of the insect, resulting in suffocation. To be most effective, horticultural soaps must be applied vigilantly and thoroughly and may need to be reapplied weekly until you attain the desired result.

Insecticidal soaps also have a beneficial effect in the removal of sooty mold, honeydew and other leaf fungi.

Soap Spray for Plants

Insecticidal soap may be made at home using ingredients which are commonly used and found around the house. That said, most garden professionals recommend using a commercial soap spray for plants, which is specifically formulated for this purpose and is safer to use with more predictable results.

Commercially formulated horticultural soaps are readily available at most garden supply stores and are sold as either a concentrate or ready-to-use (RTU). Several soap sprays for plant varieties available to the home gardener include:

  • Bonide Multi-Purpose Insect Control Soap Concentrate
  • Safer Rose & Flower Insect Killer Concentrate
  • Schultz Garden Safe Insecticidal Soap Insect Killer RTU
  • Safer Insect Killing Soap RTU

How to Make Insecticidal Soap

There are several ways to make an insecticidal soap. The choice depends on the ingredients on hand and the extent to which one wants to use natural ingredients, i.e. those without perfumes or dyes.

To make insecticidal soap, simply mix the following horticultural soap recipe ingredients thoroughly:

  • Combine one cup of oil, any variety, such as vegetable, peanut, corn, soybean, etc. with one tablespoon of dishwashing liquid or other “pure” soap (Dawn, Ivory and Lemon Joy are mentioned on many internet sites). Be sure to avoid any dish washing liquids which contain degreaser, bleach, or those that are for an automatic dishwasher.
  • Mix two teaspoons of this “soap” mixture to every cup of warm water and put into a spray bottle. Mix only what is needed for a one-day application.

Alternate Horticultural Soap Recipe

Homemade horticultural sprays can also be made using a natural soap product such as Dr. Bronner’s Pure Castile Soap or other soap without synthetic additives or perfumes, which can be found in a local natural food store.

Combine one heavy tablespoon of liquid soap to one quart of warm water. Tap water is okay to use, but if you have hard water you may want to substitute bottled water to avoid any soap scum buildup on foliage.

To either of these soapy concoctions, a teaspoon of ground red pepper or garlic may be added to further repel chewing insects. Also, a teaspoon of cider vinegar may be added to assist in the removal of powdery mildew. Bar soap may also be used in a pinch by placing into a gallon of water and leaving to sit over night. Remove the bar and shake well before use.

There are few limitations to horticultural soaps but be sure to wet the insect and be aware 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 degrees F.

BEFORE USING ANY HOMEMADE MIX: It should be noted that anytime 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. In addition, 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 burning of the plant and its ultimate demise.

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