Small dark flies rising from potting mix are often fungus gnats. Identify them before treating: adults are usually a nuisance, while larvae live in the mix and can damage young roots. Start by reviewing moisture and hygiene, then monitor progress.
What are the small flies in your indoor plants?
Fungus gnats. They’re a few millimetres long, dark grey to black, weak and wandering in the air, and they drift up from the pot when you water or walk past. If you’ve been searching for little black flies in plant soil, this is almost certainly them.
Two quick checks separate them from fruit flies. Fungus gnats stay close to the pot and wander across the surface of the mix on foot; fruit flies are quicker, browner, and hang around the fruit bowl instead. If the cloud lives over your Monstera rather than your mangoes, it’s gnats.
Now the reassuring part. Adult fungus gnats are harmless. They don’t bite, they don’t sting, and they don’t chew leaves. They’re an annoyance, and a very honest report on your watering, which is what the rest of this post is about.
Why do fungus gnats keep coming back?
Because the flies you can see are the smallest part of the problem. Fungus gnats breed in potting mix that stays permanently wet at the surface, so while you’re swatting adults, the next generation is already in the pot, living in that top layer of damp mix.
That’s why swatting, sprays and open windows never seem to work for long. Nothing you do to the adults changes the wet layer they came from, and more emerge to take their place. The gnats are the symptom. The wet surface is the problem.
There’s a second reason to take the hint. Mix that never dries at the top is usually staying too wet further down as well, and that’s the road to root rot. Our guide to how often to water indoor plants can help you review moisture and drainage.
How do you get rid of fungus gnats?
Start by reducing suitable breeding conditions and monitoring adults. Check every pot nearby, because flies can move between plants. These four steps can help, but persistent infestations may need targeted larval control.
- Let the surface dry as far as the plant tolerates. Check the species care guide and moisture below the surface. Avoid keeping the mix constantly saturated, but do not drought-stress a moisture-loving plant to treat gnats.
- Water according to the plant’s needs. Bottom-watering may help in some pots, but it can still wet the surface and is not a guaranteed two-week cure. Drain thoroughly and avoid leaving roots standing in water.
- Remove decaying material and check the mix. Clear fallen leaves and use suitable potting mix. Decorative top-dressing can make moisture harder to judge, so do not rely on a layer of pebbles or bark to eliminate an infestation.
- Monitor with yellow sticky traps. Keep traps away from pets and use catches to track adults. Persistent infestations may need additional targeted control; seek advice from a local nursery about a suitable option.
When is fungus gnat season in Australia?
Spring and summer. Warmth speeds everything up for a fungus gnat, and Australian conditions hand them two peak seasons back to back.
Warmer conditions can increase activity, but drying rates also depend on light, pot size and heating. Check the pots themselves rather than changing watering by a fixed seasonal amount.
Warm indoor conditions can support fungus gnats for much of the year. Monitor damp pots and adjust care to the actual drying rate rather than assuming a fixed pest season.
How can you reduce the risk of fungus gnats?
Keep the watering honest, and make arrival difficult.
- Check moisture before watering. Follow the drying guidance for each species and empty excess water from cover pots and saucers.
- Empty the saucer within half an hour of watering, so the pot isn’t left sitting in its own bathwater.
- Quarantine new arrivals. Gnats usually hitch in on a new plant or an opened bag of mix, so give any newcomer a fortnight on its own before it joins the shelf, and keep opened bags of potting mix sealed and dry.
- Do a weekly once-over. Wiping the dust off leaves is when you’ll notice one stray fly rather than a cloud of them, and the same habit catches mealybugs, scale and spider mites in week one instead of week six.
Most indoor plants also prefer things drier than a nervous waterer allows. Our Ficus Umbellata card says it plainly:
“I’ll take medium light and prefer to dry out between sparing drinks.” (from our Ficus Umbellata care card)
For anything else going wrong on the same shelf, start at Plant First Aid, our index of symptoms and fixes.
What we keep on the shelf for this
Two things earn their spot here, and both are about prevention rather than rescue. A 4-in-1 smart sensor settles the wet-or-dry question below the surface, where the finger test runs out of finger. And a bottle of leaf shine with a soft cloth keeps the weekly once-over honest, because clean leaves are how the first sign of any pest gets spotted early.
Everything we send is dispatched from our Queensland nursery in low-waste, plastic-free packaging, typically 3–5 business days of courier transit to most metro areas after dispatch, plus packing time.
Fungus gnat FAQs
Do fungus gnats damage indoor plants?
Adults generally do not damage leaves, but larvae can feed on roots and are more concerning for seedlings, cuttings and stressed plants. Persistent numbers warrant checking the roots and growing conditions.
Where do fungus gnats come from in the first place?
Usually with something new: a new plant, or an opened bag of potting mix that’s been sitting damp in the shed. They can also drift in through an open window in the warmer months. Wherever the first few came from, damp organic growing media can provide suitable breeding conditions. Review moisture and hygiene without assuming that every infestation means the plant has been overwatered.
Will fungus gnats go away on their own?
Numbers may fall when breeding conditions become less suitable, but established infestations can persist. Adjust moisture within the plant’s needs, monitor adults and seek advice about targeted control if numbers remain high.
The Good Plant Co nursery team · our roots · Last updated 12 September 2026
For identification and control options, see the RHS fungus gnat guide. Let the surface dry only as far as your plant tolerates; avoid drought-stressing moisture-loving plants.