Houseplant gnats are small flies that jump and fly across the soil surface and often lay eggs in the top 2 to 3 inches of the potting soil. Houseplant gnats cause little or no injury to houseplants but they do create a serious nuisance problem, mostly during winter and early spring. Since these insects develop in potting soil, virtually any houseplant can be a host for gnats. You can rid your plants of gnats without damaging them by using hydrogen peroxide.
Check the plant for dryness by placing your finger about 2 inches into the soil. If the soil is damp, avoid watering it for a couple days.
Combine 1 oz. of hydrogen peroxide with 1 qt. of water in a water pitcher.
Water the infested houseplants with the hydrogen peroxide mixture as you would ordinarily with water. The hydrogen peroxide will kill the gnats on the top of the soil and it will kill the larvae as it soaks down into the soil.
Check the houseplants regularly for gnat activity. Continue to water the plants with the hydrogen peroxide mixture once each week.