Fungus gnats in houseplant soil: why they appear and how to get rid of them

Fungus gnats are small dark flies that hover around houseplant soil; their larvae live in the top layer of damp potting mix. They mainly mean the soil stays wet, so letting the top few centimetres dry between waterings, with yellow sticky traps for the adults, is usually the first thing to try.

What does it look like?

Small dark flies around the pot, or rising when you water.
Tiny clear larvae with dark heads in the top layer of soil.
Seedlings or young plants wilting with no other cause.

Why does it happen?

Soil that stays wet near the surface.
Potting mix rich in organic matter, or new bags of soil.
Low light, so the soil dries slowly.

What can you do about it?

Let the top few centimetres of soil dry out between waterings; larvae need moist soil to survive.
Water from below for a few weeks so the surface stays drier.
Use yellow sticky traps near the soil to catch adults.
Remove standing water from saucers and cover pots.
If they persist, repot into fresh, well-draining mix.

When you photograph a plant with this problem, Leafsight gives an assessment that names the likely problem, how serious it looks and how sure it is. Your first assessment that finds a problem includes care steps like these; with Pro or a one-time unlock, every one does.

When should you look closer?

Gnats together with yellowing, drooping leaves: check for root rot.

Questions

Are fungus gnats harmful to plants?

Adult fungus gnats are a nuisance rather than a threat to the plant: they don't feed on leaves. Their larvae live in the top layer of wet soil and mostly feed on organic matter, but large numbers can damage the fine roots of seedlings and young plants. Above all, fungus gnats are a sign that the soil stays damp, which is worth fixing for the plant's sake.

How do I get rid of fungus gnats in houseplant soil?

Break the fungus gnat life cycle by letting the top few centimetres of soil dry out between waterings, since the larvae need moist soil. Water from below for a few weeks, empty standing water from saucers and cover pots, and place yellow sticky traps near the soil to catch adults. If they persist, repot into fresh, well-draining mix.

Why do I have fungus gnats in winter?

In winter, houseplants use water more slowly because there is less light, so the soil stays wet near the surface for longer. That damp top layer is where fungus gnats lay their eggs, and a new bag of potting mix can bring them in too. Water less often in the darker months and let the surface of the soil dry before watering again.

Are fungus gnats the same as fruit flies?

No. Fungus gnats are small, dark, slender flies that hover around houseplant pots and rise from the soil when you water. Fruit flies are a little stockier, often with red eyes, and gather around ripe fruit, bins and drains. If the flies stay close to your plants and you see tiny larvae in the top of the soil, fungus gnats are the likely cause.

Can fungus gnats spread to my other plants?

Yes. Adult fungus gnats fly between pots and lay their eggs in any soil that stays moist, so several plants in one room are often affected together. Letting the top few centimetres of soil dry out in every pot, emptying saucers and cover pots, and placing sticky traps near each plant helps stop them moving from one to the next.

Not sure? Check with a photo

Leafsight looks at a photo of the leaf, asks a few questions about light, watering and drainage, and gives an assessment of the likely problem with care steps. A photo assessment can be wrong: for a hands-on look, ask a local garden centre or plant clinic.

Sources

Updated 2026-11-04. All plant problems.

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