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.
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