How to Get Rid of Fungus Gnats on Houseplants

If you have houseplants, you have probably met fungus gnats. They are the tiny black flies that buzz around your plants, hover near the compost and somehow always appear just when you sit down with a cup of tea.

The good news is that fungus gnats are usually more annoying than dangerous. The adults do very little damage, but they lay eggs in damp compost and the larvae can cause problems, especially for young plants, seedlings or plants that are already struggling.

Need help with fungus gnats?
Start with our Super Ninja Fungus Gnat Traps to catch adult flies, then adjust your watering routine to stop them coming back.

What are fungus gnats?

Fungus gnats, also known as sciarid flies, are small black flies that live around damp compost. They are often mistaken for fruit flies, but fungus gnats are usually found close to houseplants rather than fruit bowls or bins.

They lay their eggs in the top layer of moist compost. Once hatched, the larvae feed on organic matter in the soil and, in some cases, delicate young roots.

Good to know: fungus gnats are usually a sign that compost is staying too wet for too long.

How to spot fungus gnats

Common signs include:

Tiny black flies hovering around houseplants
Flies appearing when you water
Small flies sitting on the compost surface
Fine white larvae in the top layer of damp compost
Plants staying wet for longer than expected

If you are seeing lots of small flies around your houseplants, fungus gnats are probably the culprit.

Step 1: Let the compost dry slightly

The first and most important step is to adjust your watering. Fungus gnats love damp compost, so allowing the top layer to dry between waterings makes the environment less appealing.

This does not mean neglecting your plants. It simply means checking the compost properly before watering again.

For most houseplants, push your finger into the compost by around an inch. If it still feels damp, leave it a little longer.

If you are unsure, our guide on how to water houseplants is a good place to start.

Top tip: overwatering is the main reason fungus gnats keep coming back.

Step 2: Use yellow sticky traps

Yellow sticky traps are one of the easiest ways to reduce adult fungus gnats. The flies are attracted to the colour and become stuck to the trap.

Sticky traps will not kill the larvae in the compost, but they do reduce the number of adult flies and help you monitor whether the problem is improving.

Place the traps close to the compost surface and replace them when they become full.

Step 3: Remove or refresh the top layer of compost

Because fungus gnats lay their eggs in the top layer of compost, removing the top inch can help reduce larvae and eggs.

Carefully scrape away the top layer and replace it with fresh compost, grit or a suitable top dressing.

A drier, less organic surface makes it harder for fungus gnats to settle and lay more eggs.

Step 4: Try bottom watering

Bottom watering can be useful because it allows the roots to take up moisture while keeping the compost surface drier.

To bottom water, place the nursery pot in a shallow bowl of water for around 20 to 30 minutes, then allow it to drain fully before returning it to its decorative pot.

This works well for many houseplants, but it is still important not to leave plants sitting in water for long periods.

Step 5: Be careful with home remedies

You may see advice online suggesting apple cider vinegar traps, cinnamon or other household remedies. Some can help catch adult flies or discourage them temporarily, but they rarely solve the whole problem on their own.

The most reliable approach is usually a combination of:

Better watering habits
Sticky traps for adult flies
Drying the compost surface
Refreshing the top layer of compost if needed

Worth knowing: fungus gnats are rarely fixed overnight. You usually need to break the lifecycle over a few weeks.

Should you use pest sprays?

Fungus gnats are different from pests such as thrips, spider mites and mealybugs because the problem is mainly in the compost rather than on the leaves.

For other common houseplant pests, products such as SB Invigorator Spray and Pepin Neem Oil can be useful as part of a regular care routine.

For more help identifying pests, read our guide to common houseplant pests.

How to stop fungus gnats coming back

The best long-term prevention is better watering. Fungus gnats thrive when compost is kept constantly damp, especially in darker rooms or during winter when plants are growing more slowly.

To reduce the chance of them returning:

Check compost before watering
Avoid watering to a strict schedule
Let the top layer dry between waterings
Use pots with drainage holes
Empty decorative pots after watering
Keep an eye on new plants brought into your home

Frequently Asked Questions

Are fungus gnats harmful to houseplants?

Adult fungus gnats are mostly harmless, but the larvae can damage delicate young roots if the infestation is severe or the plant is already stressed.

Why do I keep getting fungus gnats?

Fungus gnats usually appear when compost stays too damp. Overwatering, poor drainage and cool darker rooms can all make the problem worse.

Do yellow sticky traps get rid of fungus gnats?

Sticky traps help catch adult flies, but they work best alongside improved watering and drying the compost surface.

Should I repot a plant with fungus gnats?

Not always. In many cases, adjusting watering and using sticky traps is enough. If the compost is very wet, compacted or sour-smelling, repotting may help.

Are fungus gnats the same as fruit flies?

No. Fungus gnats are usually found around damp houseplant compost, while fruit flies are more often found around fruit, bins or kitchen waste.

Your Fungus Gnat Checklist

Let the top layer of compost dry between waterings
Use yellow sticky traps to catch adult flies
Refresh the top layer of compost if needed
Try bottom watering to keep the surface drier
Avoid leaving plants sitting in water
Check new plants before placing them near your collection
Be patient and repeat the process for a few weeks

Get Rid of Fungus Gnats for Good

Fungus gnats are annoying, but they are very common and usually manageable. The key is to make the compost less inviting, catch the adult flies and avoid overwatering.

Start with our Super Ninja Fungus Gnat Traps, browse our Indoor Plant Care collection or read our full guide to common houseplant pests.