I use dish washing soap diluted with water to spray my flowers and bushes for insects and have good results. My daughter used an anti-bacterial dish washing liquid and killed everything in her garden. What went wrong?
Homemade soap sprays can be a good, easy way to control soft-bodied insects such as aphids and spider mites in the garden. After all, everyone has some dish washing liquid on hand, right? But there are some things to be aware of when applying them.
The soap kills soft-bodied insects by breaking down its protective cuticle or skin. You must make sure that the soapy water comes into contact with the bug for this to happen. You are also spraying your plants so they are affected by the ingredients in the soap spray as well. Depending on what those ingredients are, they can break down the cuticle on your plants as well as the bugs. The best thing to do is to test the spray you have made on a few leaves and wait for 24 hours to see if there is any damage. And make sure the dish washing liquid is pure soap. Nowadays many soaps have extra ingredients in them. Avoid products with degreasers and anti-bacterial agents as these could harm your plants.
Other considerations are not to spray in the full sun, when the temperature is above 90 degrees or the humidity is very high. Make sure your plants are not drought stressed and do not repeat the spray too often. If you’re not sure about conditions, you can always ‘wash’ your plants a couple of hours after by giving them a good rinse with clear water.
One recipe I like to use is to mix 2 teaspoons of dish washing soap with 1 quart of water. Or you can try 1 part rubbing alcohol with 3 parts of water. And remember to spot test!