What is the fastest way to get rid of fungus gnats?

Combine three things at once. Let the top 3 to 5 cm of soil dry before watering, put yellow sticky traps at soil level to catch adults, and water with a BTI product such as mosquito bits steeped in water to kill larvae. Repeat the BTI every five to seven days for three or four weeks to cover the whole life cycle.

Are fungus gnats harmful to plants?

Adults are harmless nuisances. The larvae live in the top layer of soil and mostly eat fungi and decaying matter, but in large numbers they also chew fine roots. That matters most for seedlings, cuttings and young plants, which can wilt or stall.

Why do I have fungus gnats in my house?

They breed in damp potting soil, especially soil rich in peat, compost or bark that stays wet near the surface. They often arrive in a new plant or a bag of compost, and an overwatered pot lets numbers explode within a few weeks.

Does hydrogen peroxide kill fungus gnat larvae?

A drench of 3 percent hydrogen peroxide diluted with about four parts water kills larvae it touches, and you may see fizzing. It is a short-term fix. It does not stop adults laying more eggs, so you still need to dry the soil and trap adults. BTI is the more targeted option.

How do I tell fungus gnats from fruit flies?

Fungus gnats are slim, dark grey to black, with long legs and long antennae, and they hover around plant pots and windows. Fruit flies are rounder, tan or brown, often with red eyes, and gather around fruit bowls, bins and drains.

Will fungus gnats go away on their own?

Rarely, as long as the soil stays damp. Each female can lay up to a couple of hundred eggs, and the cycle from egg to adult takes three to four weeks at room temperature. Changing how you water is what breaks the cycle.

Fungus Gnats in Houseplants: How to Get Rid of Them

To get rid of fungus gnats in houseplants, you need to tackle adults and larvae at the same time: let the top few centimetres of soil dry out between waterings, catch adults with yellow sticky traps, and kill larvae in the soil with a BTI drench repeated weekly for about a month. Then keep them away by watering less often, bottom watering and using fresh, well-draining mix.

Fungus gnats (mostly Bradysia species) are the little black flies that rise out of a pot when you water it or drift around your screen in the evening. They're annoying rather than dangerous, but a bad infestation can damage the roots of seedlings and cuttings. The good news is they are one of the easiest houseplant pests to beat once you understand their life cycle.

The fungus gnat life cycle and why it matters

Stage	Where it lives	How long (room temperature)	What kills it
Egg	Top 2–3 cm of moist soil	3–6 days	Dry soil surface
Larva	Top 5 cm of soil	10–14 days	BTI, dry soil, nematodes, hydrogen peroxide
Pupa	In the soil	3–7 days	Dry soil (partly)
Adult	Flying around plants and windows	About 1 week	Sticky traps

A whole generation takes three to four weeks. Adults only live for about a week, but each female lays her eggs in damp soil before she dies. That's why spraying adults alone never works: there's always another wave hatching underneath. Any plan needs to last at least four weeks.

Step-by-step: how to get rid of fungus gnats

1. Let the soil surface dry

This is the single most important step, according to extension services including Colorado State and the University of Minnesota. Eggs and young larvae need moisture to survive, and dry soil is less attractive to egg-laying females.

Wait until the top 3 to 5 cm of soil is dry before watering.
Empty saucers and cover pots after watering.
Move plants to a brighter or warmer spot if their soil takes more than a week to dry.

Some plants, such as ferns and calatheas, dislike drying out. For those, bottom watering (next step) is the better option.

2. Water from the bottom

Stand pots in a tray of water for 15 to 30 minutes so the roots get water but the surface stays drier. Pour away the leftover water. This alone cuts gnat numbers noticeably in a couple of weeks.

3. Trap the adults

Put yellow sticky traps on stakes just above the soil, or lay small squares flat on the soil surface. Replace them when they're covered. Traps don't solve the problem alone, but they reduce the number of females laying eggs, and they show you whether numbers are going down. Count the catch each week.

4. Kill the larvae with BTI

Bacillus thuringiensis subsp. israelensis (BTI) is a naturally occurring bacterium that kills the larvae of mosquitoes, black flies and fungus gnats. It doesn't harm plants, people or pets, which is why it's the first choice for indoor use.

How to use it:

Buy a BTI product sold as mosquito bits, dunks or a liquid such as Gnatrol.
For granules, steep a tablespoon in about 4 litres of water for 30 minutes, then use the water (strained or not) to water your plants normally.
Water enough to wet the top few centimetres where the larvae live.
Repeat every five to seven days for four weeks. BTI breaks down quickly and doesn't touch eggs or pupae, so repeat treatments catch each new hatch.

5. Cover or replace the top layer

A 1 to 2 cm layer of coarse sand, fine grit or aquarium gravel on the soil makes it harder for females to lay eggs and keeps the surface drier. For badly infested pots, scrape off the top 3 to 5 cm of soil, bin it outside, and replace with fresh mix before adding the grit layer.

6. Repot only if the soil is waterlogged

If the mix is old, dense and stays wet for days, repot into fresh, well-draining mix. Our houseplant soil mix guide explains what to use. Don't repot every plant in a panic; drying and BTI usually work without it.

Fungus gnat treatments compared

Treatment	Targets	How well it works	Notes
Letting soil dry	Eggs, larvae	Very well	Free; the foundation of any plan
Bottom watering	Eggs, larvae	Well	Keeps roots watered, surface dry
Yellow sticky traps	Adults	Moderately	Monitoring tool as much as control
BTI (mosquito bits, Gnatrol)	Larvae	Very well	Repeat every 5–7 days
Beneficial nematodes (Steinernema feltiae)	Larvae	Well	Live product; good for large collections
Predatory mites (Stratiolaelaps)	Larvae, pupae	Well	Used in greenhouses
3% hydrogen peroxide drench (1:4)	Larvae it touches	Short-term	No residual effect
Grit or sand top layer	Egg laying	Moderately	Helps with prevention
Cinnamon, vinegar traps	Adults	Weak	Apple cider vinegar traps catch fruit flies better
Insecticide sprays	Adults	Short-term	Labelled houseplant products only; rarely needed

Wisconsin Horticulture Extension notes that chemical controls are rarely justified for houseplants unless an infestation is severe, and should always be used alongside watering changes.

Fungus gnats vs fruit flies vs drain flies

Feature	Fungus gnat	Fruit fly	Drain fly
Look	Slim, dark, long legs, mosquito-like	Rounder, tan, red eyes	Fuzzy, moth-like wings
Where you see them	Around pots, windows, screens	Fruit bowl, bins	Bathroom and kitchen drains
How they fly	Weak, short hops	Fast, darting	Short, jerky hops
Breed in	Damp soil	Fermenting food	Gunk in drains

If the flies hang around your fruit bowl rather than your plants, they're fruit flies, and you need to clear ripe fruit and set a vinegar trap instead.

How to prevent fungus gnats coming back

Water by checking, not by schedule. The watering schedule tool gives a starting interval, but always feel the soil first.
Use a well-draining mix. Add perlite or bark so the surface dries faster. The soil mix calculator helps with ratios.
Don't oversize pots. A pot much larger than the root ball holds wet soil roots can't use. See the repotting pot size calculator.
Quarantine new plants for two weeks and put a sticky trap in each one.
Store compost bags sealed and outside if you can.
Clear fallen leaves from the soil surface.
Give plants more light so soil dries faster. Plants in very dim spots are the worst for gnats.

A four-week fungus gnat plan

Week	What to do
1	Place sticky traps. Scrape off the top layer in the worst pots. First BTI watering. Start bottom watering.
2	Second BTI watering. Count adults on traps. Replace full traps.
3	Third BTI watering. Numbers should be falling clearly. Add grit top layer.
4	Fourth BTI watering. Keep traps out for another two weeks to confirm they're gone.

If you're still catching plenty of adults after four weeks, look for a missed source: a plant in another room, a cover pot with standing water, or an open bag of compost.

When fungus gnats are a sign of something else

A pot full of gnats is often a sign the soil is staying too wet for the plant's health, not just a pest problem. If the plant also has yellow leaves, soft stems or a sour smell, check the roots. Our overwatered plant signs and root rot guide walk through what to look for. For other pests, see the houseplant pests guide.

Sources and further reading

University of Minnesota Extension: How to treat fungus gnats in houseplants, for drying soil, barriers and BTI.
Colorado State University Extension: Fungus gnats as houseplant pests, for life cycle and control options.
Wisconsin Horticulture: Fungus gnats on houseplants, for BTI timing and when chemicals are justified.
UC Statewide IPM Program: Fungus gnats, for biological controls including nematodes.