Make a 2% insecticidal soap by mixing 5 tablespoons of soap in 1 gallon of water. Spray as required. The fatty acids in the vegetable oil or animal fat contained in soap is responsible for the insecticidal properties. Use Castile or some other pure liquid soap for best results.
1 Mix warm water with liquid dish soap or castile soap, at a rate of 2 tablespoons of soap for every 1 gallon of water. Avoid antibacterial soaps and soaps with fragrance or moisturizers.
2 Add up to 2 tablespoons of cayenne pepper powder, depending on the severity of the infestation. For a smaller batch, use a teaspoon of dish soap and a pinch of cayenne pepper in a 1-quart spray bottle filled with water.
3 Test the spray on a few small leaves 24 to 48 hours before spraying an entire plant. Don’t spray the plants if the leaves look damaged or burned, as some plants are sensitive to soap.
4 Spray the plant thoroughly, coating the stems and tops and bottoms of the leaves. Allow the soap to work for about two hours, then rinse the plant with water to reduce the chance of injury. Spray when the plant is in the shade to prevent scorching the plant.
5 Reapply the insecticidal soap mixture every four to seven days. Soap sprays kill only on contact and have no residual effect once the spray is dry.
Dawn liquid dish detergent in approximately a 2 percent concentration is a fairly safe alternative to commercial insecticidal soaps formulated to kill insects such as aphids, mites and scale on plants and keep them away.
For a 1 percent solution of Dawn soap spray, mix 2 1/2 tablespoons of detergent in 1 gallon of water. Add another 2 1/2 tablespoons per gallon for each 1 percent you wish to strengthen the solution, up to a 4 percent mixture.
Homemade Insecticidal Soap Recipe Variations
Like any other home remedy, there are as many variations on this recipe as there are gardeners! You can also try:
- Diluted Solution: If the spray causes damage or burns your plant foliage, cut the amount of soap in half and try a 1% solution. This is the concentration usually found in commercial sprays. The lighter solution might be less effective but is gentler on plants.
- Cooking Oil: To help the solution stick a little longer, add two tablespoons of light cooking oil (such as corn, canola, olive, or safflower) per gallon of water to the mix.
- Vinegar: To make a spray that also targets powdery mildew, add a teaspoon of cider vinegar per gallon of water to the mix.
- Garlic or Pepper: To help repel chewing insects, add a teaspoon of ground red pepper and/or garlic per gallon of water to the mix.
- Bar Soap: For a less-exact recipe, drop a bar of pure soap (such as organic bar soap or Ivory) into a gallon of water and leave it overnight. Remove the bar and shake well before spraying.
- How To Use Insecticidal Soap on Plants (article)
- Control Houseplant Insect Pests Safely with Insecticidal Soap (Iowa State)
- Organic Pest Control (video)
- Organic Gardening 101 (article)
- Is Pyrethrum a Safe Organic Pesticide? (article)
- How to Use Neem Oil in Your Garden (article)
Safe Rose Spray Recipe That Really Works
More than 5,000 rose bushes grow at Hershey Gardens in Hershey, Pa., where the gardening staff works hard to keep them free of pests and diseases. They use a chemical spray in the main garden, applying it every week or so and just after a rainstorm. They did not want to use this spray in the dedicated Children’s Garden, so they came up with the following safe rose spray recipe, which they’ve found to be very effective:
Mix one tablespoon of vinegar with one cup of water. Add one and a half tablespoons of baking soda plus one tablespoon of dish soap and one tablespoon of vegetable oil (or any other cooking oil).
Stir this mixture into one gallon of water, and spray it on your roses’ foliage.