Those tiny black flies hovering around your pots are fungus gnats, and they are telling you one thing: your topsoil stays wet too long. Adults are harmless but annoying; the real damage comes from larvae chewing fine roots in soggy soil. Traps alone never work because they ignore the larvae. This 4-step method breaks the whole life cycle in 3–4 weeks.

Step 1: Dry the top (kills eggs)

Let the top 3–5 cm of soil dry completely between waterings — gnat eggs and larvae need constant moisture. Switch susceptible plants to bottom watering so the surface stays dry. Remove dead leaves from the soil surface. If you are a chronic overwaterer, read the overwatering signs first — gnats are often symptom #1.

Step 2: Trap the adults (stops new eggs)

Place yellow sticky traps just above the soil in every affected pot. One trap per pot, replaced weekly. This doesn't cure anything alone, but each trapped female lays ~200 fewer eggs, and trap counts tell you whether the population is falling.

Step 3: Kill the larvae (the actual cure)

Water once with Bti (Bacillus thuringiensis israelensis) — sold as mosquito bits/dunks — soaked per label directions. Bti is a bacteria toxic only to fly larvae: safe for plants, pets, and people. Repeat for 2–3 waterings to catch hatching eggs. Beneficial nematodes (Steinernema feltiae) are the premium alternative for severe cases.

Step 4: Prevent return

  • Top-dress with 1–2 cm of coarse sand or fine gravel — females can't reach damp soil to lay eggs.
  • Improve drainage: gritty mix, drainage holes, empty saucers. See DIY potting mixes and choosing pots.
  • Quarantine newcomers: inspect store plants with our 10-point checklist — gnats often hitchhike home.
  • Don't overpot: huge pots stay wet for weeks. Size up only 2–5 cm at a time.

What doesn't work

Cinnamon, hydrogen peroxide drenches, and pebble layers alone have weak evidence and can harm roots or soil life. Misting with neem annoys adults at best. Stick to the 4 steps — dry, trap, Bti, prevent — and the cycle collapses within one gnat generation (~4 weeks). For lookalikes (fruit flies, shore flies), confirm with our pest identification guide.

Frequently asked questions

How long does it take to get rid of fungus gnats?

About 3–4 weeks — one full life cycle. Adults live ~1 week but eggs keep hatching, so Bti treatments must repeat across 2–3 waterings while traps catch each adult wave.

Does cinnamon kill fungus gnats?

No reliable evidence. Cinnamon may mildly suppress surface mold (their food) but doesn't kill larvae or eggs. Bti plus drying the topsoil is the proven combination.

Are fungus gnats harmful to plants?

Adults are harmless; larvae in large numbers damage seedlings and fine roots, stunting growth. Mature plants usually survive, but heavy infestations plus overwatering can tip into root rot.