Q: I saw in your email garden newsletter that you recommend commercial insecticidal soap, not home-made. Why can’t I make my own stuff?

A: I usually hear of people using dish detergent in their insecticide concoctions, which can burn plant leaves. There is a considerable difference between dish detergent, bar soap and insecticidal soap.

Despite advice from amateur sources, commercial insecticidal soaps are far superior.

What we call “soap” is a substance made by combining fat with an alkali, like sodium hydroxide, which will yield a hard soap, or potassium hydroxide, which yields a liquid soap that can be sprayed. Only a few of the many fats available have the insecticidal properties you want.

Most household soaps and detergents are mildly harmful to leaves. They are herbicides instead of insecticides. Buy brand-named insecticidal soap and be safe.

Understanding Insecticidal Soaps and Detergents