Insecticidal soaps, made from organic ingredients, are effective on a number of garden pests and safe to use on vegetables. They can be purchased at gardening centers or made at home. Many common vegetable garden insects have a protective covering on their surface that is washed away by insecticidal soaps. When used on aphids, the soap actually clogs their breathing holes, according to Farm Advisers with Washington State University. When spraying vegetable plants, spray directly on the infested surfaces. Repeated applications may be necessary.
Mix 2 tablespoons of liquid detergent in one gallon of water. Scientists at New Mexico State University suggest using Ivory Liquid dishwashing detergent. If you prefer using a certified organic soap, try Dr. Bronner's peppermint or Castile liquid soap at the same dilution rate.
Add the mixture to the spray bottle and shake it until it is completely combined.
Spray the plant with the soap completely. In order for the insecticide to be effective, all infested parts of the vegetable plant must be hit with it.
Wait three hours and then wash the insect spray off the plants with a garden hose.