How to Get Rid of Fungus Gnats: 7 Steps That Actually Work

Tiny black flies drifting up every time you water, crawling on the soil or bumping into your screen? Those are almost certainly fungus gnats, the most common houseplant pest. They are annoying, they multiply fast, and they love the same thing many indoor plants get too much of: wet soil.

The good news is that fungus gnats are easy to beat once you target the larvae living in the soil, not just the flies you can see. This guide shows you exactly how to get rid of fungus gnats in 7 simple steps, how long it takes, which home remedies actually work, and how to keep them from coming back.

What are fungus gnats?

Fungus gnats are tiny, dark grey to black flies, about 1/8 inch (3 mm) long, with long legs and see-through wings. They are weak fliers, so you usually see them walking on the soil or flying in short, zigzag hops near the pot.

The adults are harmless and only live about a week, but each female can lay 100 to 300 eggs in moist soil. The eggs hatch into tiny white larvae with shiny black heads that live in the top 1 to 2 inches of soil, feeding on fungi, decaying matter and sometimes fine roots. The whole life cycle takes about 3 to 4 weeks, which is why one treatment is never enough.

Stage	Where it lives	How long
Eggs	Top layer of moist soil	About 3 days
Larvae	Top 1 to 2 inches of soil	About 10 to 14 days
Pupae	In the soil	About 3 to 4 days
Adults	Flying around the plant, laying eggs	About 7 to 10 days

Fungus gnats vs fruit flies

Fruit flies are tan with red eyes and hang around the fruit bowl and trash. Fungus gnats are darker, slimmer, with long legs, and hang around your plants and soil. If the flies rise from the pot when you water, they are fungus gnats.

Do fungus gnats harm plants?

For most established houseplants, fungus gnats are more of a nuisance than a danger. But in large numbers the larvae can damage roots, especially on seedlings, cuttings and young plants, causing wilting, yellow leaves and slow growth. Their feeding wounds can also let root diseases in. And a fungus gnat problem is a warning sign: the soil is staying wet too long, which can lead to root rot.

How to get rid of fungus gnats in 7 steps

The secret is to attack both stages at once: trap the flying adults so they cannot lay more eggs, and kill the larvae in the soil. Work through these steps together for 3 to 4 weeks.

1. Let the soil dry out

This is the single most effective step. Fungus gnat eggs and larvae need moist soil to survive. Let the top 1 to 2 inches of soil dry completely before you water again. Push a finger into the soil, and only water when it feels dry at that depth. For plants that like to stay moist, dry just the top inch. Our watering guide explains how to tell when a plant really needs water.

2. Put up yellow sticky traps

Adult gnats are attracted to bright yellow. Stick yellow sticky traps into the soil or lay them flat just above it, one per pot or one for every couple of plants. They catch adults before they lay eggs and also show you how bad the problem is. Replace them when they are full. Traps alone will not solve the problem, because they do not touch the larvae.

3. Kill the larvae with BTi (best treatment)

BTi (Bacillus thuringiensis subsp. israelensis) is a natural soil bacterium that kills fungus gnat larvae but is safe for plants, people and pets. It is sold as mosquito bits or dunks for ponds.

1. Soak about 1 to 2 tablespoons of mosquito bits in a gallon of water for 30 minutes (or follow the label).
2. Strain or leave the bits in, and use this water for your normal watering.
3. Repeat every time you water for 3 to 4 weeks to catch every new batch of larvae.

4. Or use a hydrogen peroxide drench

A quick alternative is hydrogen peroxide. Mix 1 part 3% hydrogen peroxide with 4 parts water and water the plant when the top inch of soil is dry. It fizzes on contact and kills larvae, then breaks down into water and oxygen. Repeat once a week if needed. Test on one plant first, and avoid it on very delicate seedlings.

5. Top-dress the soil with sand or gravel

Cover the soil with a half-inch layer of coarse sand, fine gravel or decorative grit. The surface stays dry, so adults cannot lay eggs and new adults struggle to climb out. Do not use bark or moss as a top layer, because they hold moisture and attract gnats.

6. Try a vinegar trap for adults

Fill a small dish with apple cider vinegar and a drop of dish soap, and set it next to infested plants. Adults are drawn to the smell and drown. It is a helpful extra, but like sticky traps it does not reach the larvae.

7. Repot badly infested plants

If a pot is crawling with larvae, the soil is soggy, or the plant is small, repot into fresh, dry, well-draining mix. Gently remove as much old soil as possible, rinse the roots if needed and use a clean pot. See our repotting guide and potting soil guide for the best mix.

Home remedies: what works and what does not

Remedy	Does it work?	Notes
Letting soil dry out	Yes, very well	The foundation of every treatment.
Yellow sticky traps	Yes, for adults	Catch flies and show how bad it is; do not kill larvae.
BTi (mosquito bits)	Yes, very well	Best larvae killer; safe for plants and pets.
Hydrogen peroxide drench	Yes	1 part 3% peroxide to 4 parts water; repeat weekly.
Beneficial nematodes	Yes	Steinernema feltiae hunt larvae; great for large collections.
Sand or gravel top layer	Yes, as prevention	Keeps the surface dry so gnats cannot lay eggs.
Apple cider vinegar trap	Partly	Catches some adults only.
Cinnamon on soil	Little evidence	May slow fungus on the surface, but will not clear an infestation.
Neem oil soil drench	Partly	Can reduce larvae but less reliable than BTi.

How to prevent fungus gnats

• Do not overwater. Water only when the top of the soil is dry. Overwatering is the number one cause.
• Bottom water plants that allow it: set the pot in a tray of water for 15 to 30 minutes so the roots drink while the surface stays drier.
• Use a well-draining mix and pots with drainage holes; empty saucers after watering.
• Store potting mix sealed and dry. Opened bags are a common source of gnats.
• Check new plants before bringing them home, and keep them apart for a week or two.
• Remove dead leaves and debris from the soil surface.
• Water less in winter, when soil dries more slowly. See our winter care guide.

If a plant looks badly damaged, our guide on how to revive a dying houseplant can help. For other bugs like mealybugs, spider mites and scale, see our complete houseplant pests guide.

Are fungus gnat treatments safe for pets?

Most of the methods here are pet-friendly. BTi only affects the larvae of certain flies and mosquitoes and is considered safe around cats and dogs. Keep sticky traps out of reach, because fur and paws get stuck on them, and keep peroxide and vinegar dishes where pets cannot drink them. Looking for plants that are safe too? See our pet-friendly houseplants.

Quick action checklist

Fungus gnats FAQ

Sources and further reading

Want to go deeper? These university extension and expert resources cover the same topic:

• UC Statewide IPM Program: Pest Notes: Fungus gnats
• Oregon State University Extension: I have fungus gnats everywhere. Can you help?
• UC Statewide IPM Program: Pest Notes: Houseplant problems (PDF)