How to Treat Insects in Houseplant Soil

Let the soil dry out as much as possible, preferably until it is completely dry. Keeping the soil dry between waterings will kill fungus gnats, which feed on the fungus that grows in wet soil.

Mix Bacillus thuringiensis (BT) according to the label directions. Add 1 teaspoon of dish washing liquid per 1 gallon of the mixture. Perform a soil drench by pouring the solution through the container three times. BT is a bacterium that infects and kills fungus gnat larvae and eggs.

Mix insecticidal soap according to the label directions and drench the soil by pouring it through the container three times. This solution kills springtail larvae but not their eggs so repeat the application every 10 days until they are eradicated.

Make a solution of liquid systemic insecticide with acephate, according to the label directions. Add 1 teaspoon of dish washing liquid per 1 gallon of solution to help it stick to the soil. Drench the soil with the solution to control root aphids, silverfish and young cockroaches. This is a persistent pesticide that lasts a long time in the soil, so one application is sufficient.

Lay cockroach traps around large potted indoor plants to catch cockroaches that live in the soil. Hang sticky traps from the branches and lay them on the soil surface of indoor plants to catch adult fungus gnats.