How to Make Insecticidal Soap, a Natural Way to Remove Bugs From Your Houseplants

Insects are an inevitable aspect of owning houseplants, but major infestations can threaten the health of your plants. One way to remove these pests is with insecticidal soap. The product contains potassium salts of fatty acids that are effective at killing soft-bodied bugs, like aphids and spider mites. While insecticidal soap is available at most nurseries and online, the natural spray can easily be made from home with just two ingredients—distilled water and soap.

How Insecticidal Soap Works

Insecticidal soap can kill many soft-bodied insects that pose a threat to your plants. "The soap contains fatty acids that remove a protective layer from the outside of the insect and then damage the interior cells, causing a quick death," says Ryan McEnaney, garden designer and author of Field Guide to Outside Style: Design and Plant Your Perfect Outdoor Space. When their exoskeleton deteriorates, the insects become dehydrated and die.

Materials Needed

Make sure you have these materials on hand when making insecticidal soap.

• Spray bottle
• Distilled water
• Castile soap
• Vegetable oil (optional)
  

How to Make Insecticidal Soap

Insecticidal soap is made by combining distilled water, soap, and vegetable oil. Vegetable oil is completely optional and just helps the mixture stick to the leaf before drying. "The fatty acids in the soap are what actually kills the insect, so you can go without the oil if you don’t have it readily accessible," says McEnaney.

Always use distilled water when making insecticidal soap, as hard water can limit the benefits of the soap's fatty acids. Additionally, you should never use dishwashing detergent in place of soap, as it can harm your plants. Instead, use fragrance-free, pure Castile soap.

Only make enough insecticidal soap for one day's treatment using the following ratio. (Scale up if you have a lot of plants to treat.)

1. In a clean spray bottle, combine 1 tablespoon of fragrance-free soap per quart of water.
2. Optional: Add 1 tablespoon of vegetable oil to the soap and water mixture.
3. Shake the bottle so the mixture is well combined, and use immediately.
   

How to Use Insecticidal Soap

To use insecticidal soap, evenly spray the mixture on all surfaces that are infested with pests or harmful insects. "Be sure to hit the tops and bottom of affected leaves, as well as the supporting stems," says McEnaney. "You want to ensure there’s consistent coverage but not so much soap that it’s dripping off."

Monitor your plants for pest infestations and use the soap as needed. "You should use it as often as you see heavy infestations, which could occur possibly every two to three weeks," says Adrienne Roethling, the garden director for Paul J. Ciener Botanical Garden. "These small pests have short life cycles and can lay hundreds of eggs every other week." Avoid using insecticidal soap for just one or two bugs, as those can be picked off by hand.

Insects Insecticidal Soap Works On

Insecticidal soap is effective against soft-bodied insects. "It will help eradicate aphids, cotton scale, thrips, mealybugs, white flies, and more," says Roethling. "It will not kill pests in their egg stage or hard-shell insects." Also, keep in mind that insecticidal soap only works when these insects are present and cannot be applied as a preventative treatment.