Fungus Gnat Control – How to Spot These Tiny Terrors and Get Rid of Them Once and for All

Fungus gnats (Sciaridae family), also known as soil gnats, don’t cause very much actual damage to established houseplants. It is true that the larvae of certain species can damage the delicate root hairs of some plants, especially seedlings and succulents.

More than anything, though, they’re annoying! I have had a fungus gnat infestation before, and I did not rest until my house was free of the things. Buckle up for info on how fungus gnats take hold, and how to get rid of this all-too-common houseplant pest.

Identifying Fungus Gnats

Fungus gnats are tiny, delicate flying insects. Up close they look like miniature mosquitoes. When they buzz by your face, though, they’re more reminiscent of the gnats or midges that will drive you to your wits’ end outdoors.

Fungus gnat infestations are most common in fall and winter, though they aren’t selective about when they lay their eggs, and can pop up at any time during the year. One female can produce several generations of larvae in a single season, depositing her eggs in the top 2-3 inches (5-8 cm) of houseplant potting soil. Each generation can consist of 200 eggs, which all hatch at once a few days after they’re laid, leading to your house being suddenly overrun.

Larvae live in the soil and are identifiable as translucent white worms with black heads that leave behind slime trails on the soil’s surface.

Adults are weak flyers and usually don’t stray too far from the potted plant they call home. They will, however, be happy to invade any nearby houseplants. They’re also attracted to light, meaning you may find them clustered around lightbulbs, windows, or computer screens.

How to Get Rid of Fungus Gnats

The best way I’ve found to control fungus gnats is to invest in those sticky yellow traps (available here on Amazon). Just remove the paper cover to expose the sticky surface and stick it into the soil of your houseplant. Not only does it work, you can watch it work as the gnats immediately start piling up on it. It’s incredibly satisfying, if a little grisly.

Bacillus thuringiensis israelensis (BTI) is a more targeted approach.A naturally occurring bacterium, it specifically targets gnat larvae without harming pets or humans. You can find BTI on Amazon.

If all else fails, try repotting the plant in new soil. Remove the plant from its pot and wash away all the soil from the roots. Wash the container with a diluted solution of bleach and water. (Don’t bleach the roots!) This should kill any remaining larvae or eggs.

Repot the plant in fresh soil, and let it dry out completely before watering again. And move it somewhere far from its last spot in your house. You don’t want any remaining gnats to land on it and start laying again straightaway.

How to Prevent Fungus Gnat Infestations

Fungus gnats thrive in wet conditions, so proper houseplant watering is the first defense against them. Most plants should be watered deeply, then allowed to drain thoroughly. Always allow the top two inches (5 cm) of potting mix to dry between waterings. Be sure every pot has a drainage hole in the bottom and always empty water that drains into the drainage saucer.

I like to soak mine thoroughly in the kitchen sink – that way they get a good drenching and drain completely before they go back to their saucers.