Troubleshooting
Fungus gnats won't go away?
Written by Mustafa Ayan Fact-checked against university extension/IPM sources Last reviewed: September 19, 2026
Most "this doesn't work" reports trace back to one of a handful of causes. Run the self-check below, or scan the situations underneath it.
Quick self-check
Check what's true for you right now
Select anything that applies. Most stalled infestations trace back to one or two of these at once.
Or find your exact situation
Why do fungus gnats keep coming back after I've treated them?
Almost always one of three things: the soil surface is still staying damp between waterings, larvae already pupating when you treated have finished emerging as adults, or a second pot nearby is still infested and reseeding the room. Treat every pot in the area at once. Keep monitoring after adult numbers fall, and continue moisture management and any labeled treatment long enough to account for remaining immature stages still developing in the soil — not just until things look better.
Why aren't my sticky traps working?
Sticky traps only catch flying adults — they do nothing to eggs or larvae in the soil, which is where most of the population actually lives at any given time. A trap that stays clean can also mean the card isn't at soil level, is dusty or full, or is simply overwhelmed by egg-laying happening faster than adults are trapped. Traps are a monitoring and knock-down tool, not a standalone fix.
How long should full elimination realistically take?
You may see fewer adults within days once the mix stays dry and adults are being trapped, but complete control often takes several weeks — longer for a heavier, multi-plant infestation — because eggs and larvae already in the soil keep completing their life cycle even after you start treating. These timelines are approximate and depend on temperature and consistency of treatment; don't assume a method has failed before giving it that full window.
How do I know if larvae are still in the soil?
The classic check is the potato test: bury a half-inch cube of raw potato just under the soil surface, then check the underside after 1–2 days. Larvae are drawn to it and should be visible if present. Repeatedly finding none is a useful sign the population may be declining, but it doesn't prove the pot is pest-free — treat it as one data point, not a final verdict.
What should I do during a severe, multi-plant infestation?
Treat the whole collection at once rather than one pot at a time — gnats move freely between nearby plants. Stop watering anything that isn't visibly wilting, run sticky traps everywhere, and use a Bti product labeled for fungus gnats across every affected pot, following the current label for amount and retreatment interval rather than a fixed weekly schedule. Isolating a badly infested plant while you work on it can also slow how fast it reseeds the rest of the room. Hydrogen peroxide is an optional, cautious add-on some people use — not a required or equally-weighted step.
Is it normal to still see a few gnats for a while after treatment starts?
Yes. Adults that were already pupae when you started treating will still emerge — that's expected and not a sign the plan isn't working. What matters is the trend on your sticky cards over days, not whether the count hits zero immediately.
Still stuck despite consistent treatment? Re-check the basics with the full elimination guide — a wrong diagnosis or a missed second pot is behind most infestations that won't quit. Not sure if it's actually working or genuinely stalled? See how to know treatment is working, or confirm what's in the soil with the larvae identification guide.
Restart with the 7-day plan