From the new card deck, Eco-Clean Deck, 50 Recipes for Nontoxic Household Cleaners, by Annie B. Bond

For most garden pests you don’t need much more than soap to kill pests, but make sure not to use more than directed or you can kill the plant. Soap works as an insecticide by dehydrating the insects. I particularly like this formula because it is straightforward, safe, and simple. You can make a bigger batch, but don’t add more than 2 tablespoons of soap to a gallon of water.

Peppermint Castile Soap Spray
Makes 2 cups
Self life: indefinite
Preparation time: a few minutes
Storage: leave in the spray bottle

2 teaspoons peppermint castile soap
2 cups water

Combine the ingredients in a spray bottle. Shake, and spray infested areas.

Variations
Eucalyptus and Pennyroyal Spray: Substitute 1 teaspoon each eucalyptus and pennyroyal for the soap (avoid pennyroyal if pregnant).
Rosemary Spray: Add 1 teaspoon essential oil of rosemary

–Annie Bond