Insecticidal Soap

- An effective alternative for garden insecticides -

Summary: Insecticidal soap can be used as a safe and inexpensive alternative to garden insecticides in many pest management situations. Be cautious, however, because old, oxidized soap can damage your plants. A simple DIY test is available to protect plants from this damage.

Insecticidal soaps will not usually harm beneficial species such as predators and parasites and are generally very safe for the applicator. Soap concentrates are less expensive in the long run, and easier to store, than ready-to-use packaging. However, always do what I call a jar test to be certain that the concentrate has not spoiled.

DIY insecticidal soap "jar test"

As soap concentrate ages it oxidizes which causes it to turn dark brown. Old, oxidized soap has the potential to burn plant foliage. Solutions made from old soap concentrate often exhibit a white precipitate (see jar on right, above) when mixed with water and should be discarded. Old soap concentrate can be used as a cleaner like ordinary liquid soap just don't put it on your plants!

Using insecticidal soap in your garden

Insecticidal soap is generally used as a 1-2% solution (1-2 oz. per gallon). Mix soap concentrate in a clean 1 quart sprayer. Plan to treat in the morning of a warm day when the plants will be able to dry before evening. Spray plants with a coarse spray of plain water from the garden hose. Next, thoroughly spray plants with soap solution covering all surfaces. Finally, wait 30 minutes then wash soap off with water. The last step will prevent soap solution from damaging tender leaf tissue (see Using Insecticidal Soap To Control Aphids and Using Insecticidal Soap To Control Spider Mites for more information).