Symptoms
- Small dark gnats flying around or resting on plant soil
- Gnats more active when the plant is watered or disturbed
- Larvae sometimes visible as tiny clear worms in the top layer of soil
Likely causes
- CommonOverly moist potting soilFungus gnat larvae live in and feed on organic matter in consistently damp soil.
- CommonOverwatering habitsWatering before the top inch or two of soil dries out keeps conditions ideal for gnats to breed.
- PossibleNew plant or soil that already carried eggs or larvaeGnats can be introduced into the home through a newly purchased plant or bagged potting soil.
What to do
- Let the top inch or two of soil dry out fully between waterings, since gnat larvae can't survive in dry soil.
- Remove standing water from saucers under pots, which also supports breeding.
- Consider top-dressing the soil with a layer of sand or diatomaceous earth, which makes it harder for adults to lay eggs and larvae to survive near the surface.
- Use yellow sticky traps near affected plants to catch adult gnats and monitor how the population responds to changes.
- Repot in fresh, sterile potting mix if the infestation is heavy or soil is much older.
- Avoid overwatering going forward as the main long-term prevention step.
- Isolate a newly purchased plant for a couple of weeks before placing it near other houseplants if gnats appear soon after bringing it home.
Tools and parts
- Yellow sticky traps
Diatomaceous earthSearch: “food grade diatomaceous earth”
When to call a pro
Pest control professionals rarely need to be involved for fungus gnats; a nursery or garden center can advise on stubborn cases.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.