How do I get rid of fungus gnats on houseplants?

Let the potting media dry between waterings, especially the top 1–2 inches — Colorado State notes this reduces egg and larval survival and makes the soil less attractive to egg-laying females. Apply Bti (Bacillus thuringiensis israelensis) as a soil drench (mosquito bits work) — it kills larvae. Bti doesn’t persist indoors, so UC IPM notes repeated applications at about five-day intervals may be needed. Use yellow sticky cards near the pot to trap adults and monitor population. For severe cases, repot in fresh, well-draining mix and dispose of the old soil.

How do I prevent fungus gnats?

Avoid bagged potting mix sitting open in a humid room — it can come pre-infested. Use a well-draining mix with chunky perlite or bark so the surface dries fast. Bottom-water plants prone to gnats so the surface stays dry.

Pest identification · Bradysia spp.

Fungus Gnats on Houseplants

Fungus gnats are small dark flies (about 1/8 inch long) whose larvae live in the top 2–3 inches of moist potting media, feeding on organic matter and fine roots. The adults are mostly a nuisance; the larvae can damage seedlings and stressed plants. They indicate consistently overwet soil.

Read the full fungus gnats treatment guide

How to identify fungus gnats

Adults: small dark flies that flit around the pot and the air just above it. Larvae: tiny translucent worms with shiny black heads, found in the top layer of wet potting mix.

Damage to look for

Slowed growth in seedlings and young plants, mushroom-like off smell from the soil, occasional yellowing of lower leaves on small plants. Mature plants tolerate gnats with little damage.

Life cycle (why they spread so fast)

Egg to adult takes three to four weeks at typical room temperatures (65–75°F). During their seven- to 10-day life span, females may lay up to 200 eggs. Larvae usually stay in the top 2–3 inches of media, which is why surface-drying breaks the cycle.

How to get rid of fungus gnats

1Let the potting media dry between waterings, especially the top 1–2 inches — Colorado State notes this reduces egg and larval survival and makes the soil less attractive to egg-laying females.
2Apply Bti (Bacillus thuringiensis israelensis) as a soil drench (mosquito bits work) — it kills larvae. Bti doesn’t persist indoors, so UC IPM notes repeated applications at about five-day intervals may be needed.
3Use yellow sticky cards near the pot to trap adults and monitor population.
4For severe cases, repot in fresh, well-draining mix and dispose of the old soil.

How to prevent fungus gnats

Avoid bagged potting mix sitting open in a humid room — it can come pre-infested.
Use a well-draining mix with chunky perlite or bark so the surface dries fast.
Bottom-water plants prone to gnats so the surface stays dry.

Per-species treatment guides

Treatment varies slightly by plant. Find your species below for a dedicated guide.

Source: Colorado State University Extension — Fungus Gnats. Other figures: UC IPM — Fungus Gnats, as named in the text.