Getting Rid of Fungus Gnats in Houseplants

What Are Fungus Gnats?

Tiny (1/8″) dark flies that hover around moist potting soil. They don’t bite but are annoying. Larvae (¼″, shiny black head, translucent body) feed on fungi and organic matter in soil, sometimes damaging roots. A slime trail on soil surface is a telltale sign.

Root Cause: Overwatering

Gnats thrive in constantly moist soil. The key to control is drying out the top layer between waterings.

Control Steps

1. Reduce moisture: Water only when the top inch of soil is dry. Ensure pots drain well; empty saucers.
2. Yellow sticky traps: Place horizontally over pot rims to catch adults. Replace when covered.
3. Repot in sterile mix: If infestation persists, wash roots and repot in fresh, sterile potting soil.
4. Beneficial nematodes: Products like Scanmask or Nemasys contain microscopic worms that kill larvae without harming plants, pets, or people. Apply when soil isn’t frozen; effective for months.

Prevention

• Inspect new plants before bringing indoors.
• Use sterile potting mix when repotting.
• Avoid standing water and hose leaks in growing areas.
• Store extra potting soil dry in sealed containers.

Gnats often appear in fall when plants come inside. A dry‑soil regimen usually solves the problem.