Fungus Gnats: How to Get Rid of Them for Good

Those tiny black flies that buzz up when you move a plant are fungus gnats. They're annoying but not dangerous to a healthy plant. The key to eliminating them is understanding what they live on: moisture and organic matter on the soil surface.

Why they appear

Females lay eggs in the top inch of moist soil. The larvae feed on fungus and organic matter. That's why they almost always show up with overwatering or soil that never fully dries.

The main weapon: let the soil dry

Cut the surface moisture and you cut their cycle:

1. Space out watering and let the top 1-2 inches dry completely.
2. Water from below (via the saucer) when you can, to keep the surface dry.
3. Cover the soil with half an inch of coarse sand or grit: it stops them laying eggs.

Trap the adults

• Yellow sticky traps: fungus gnats are drawn to yellow and get stuck. They cut the population fast.
• DIY trap: a cup of apple cider vinegar with a drop of soap.

Kill the larvae

• Bacillus thuringiensis israelensis (BTI): a biological control (mosquito bits) you water in that kills larvae without harming the plant. Most effective.
• Diluted hydrogen peroxide (1 part 3% peroxide to 3-4 parts water) watered in once also kills larvae on contact.

How to prevent a comeback

• Don't overwater: it's the source of 90% of cases. See our watering guide.
• Quarantine new plants and check the nursery soil.
• Remove fallen leaves from the surface.

Combine letting the soil dry + yellow traps + BTI and they vanish in 2-3 weeks. Not sure which pest it is? Upload a photo to the AI diagnosis.