What are fungus gnats?
Fungus gnats are small, dark flies that lay their eggs in moist soil. Their larvae feed on decaying organic matter and sometimes plant roots, which can cause yellowing leaves, wilting, and slow growth.
Fungus gnats thrive in damp conditions, so overwatered plants are especially vulnerable.
How to spot fungus gnats
If you see tiny black flies around your plants or windows, you may have fungus gnats. To check, tap the pot lightly; gnats will take flight if present. You may also see tiny, white worm-like larvae on the soil surface.
How to treat fungus gnats
- Dry out the soil. Fungus gnats love moisture, so let the top 1–2 inches of soil dry completely before watering again. This disrupts their life cycle, as larvae can’t survive in dry soil.
- Use sticky traps. Yellow sticky traps, available at garden centers or online, easily catch adult fungus gnats. Place them near the base of plants and replace as needed. This reduces the number of adult gnats laying eggs.
- Top the soil with a barrier. Cover the soil with a thin layer of sand, diatomaceous earth, or fine gravel. This barrier makes it harder for adult gnats to reach the soil and lay eggs. A layer at least half an inch thick is best.
- Water from the bottom. Bottom-watering lets the plant absorb only what it needs, keeping the soil’s surface dry and discouraging gnats. Set the pot in a tray of water for 15 to 30 minutes, then remove any excess water.
- Use biological insecticides. A natural bacterium called Bacillus thuringiensis var. israelensis (BTI), found in mosquito dunks, works against fungus gnat larvae. Add a piece of a dunk to your watering can. BTI is safe for plants and pets and targets only fungus gnat larvae.
Preventing fungus gnats
After treatment, use these steps to keep fungus gnats from returning:
- Avoid overwatering. Stick to a watering schedule and use pots with drainage holes.
- Remove dead leaves and debris. Clean up dead plant material, as decaying matter attracts gnats.
- Use well-draining soil. A well-draining mix helps prevent overly moist conditions that fungus gnats love.
Fungus gnats can be annoying, but a few simple changes to your plant care routine can get rid of them. Drying out soil, using sticky traps, and treating with BTI are all effective ways to protect your plants and keep your indoor garden pest-free.
With these tips, you can enjoy your houseplants without the constant buzz of unwelcome pests.