How to Kill Gnat Larvae in House Plants
- 1). Allow the top 1 or 2 inches of soil to dry before watering houseplants. Dry potting soil is unattractive to egg-laying female fungus gnats, and their larvae can’t survive without moisture.
- 2). Re-pot plants that have been growing in the same soil for 1 or more years. Plant them in sterile potting soil or a soil-less potting medium. Over time, organic potting medium breaks down, providing food for fungus gnat larvae.
- 3). Apply a houseplant soil treatment containing Bacillus thuringiensis (Bt). Verify that the product is labeled for use against fungus gnats. Bt is a bacterium that kills fungus gnat larvae but is harmless to humans and other animals.