← the journal/guide · 11 jun 2026
fungus gnats: the full eviction plan
the tiny flies — Sciaridae (unfortunately)
fungus gnats breed in the top few centimeters of constantly moist soil. you evict them by attacking both generations at once: yellow sticky traps catch the flying adults while letting the topsoil dry out kills the larvae. do both for three weeks straight and the cycle breaks — no chemicals needed.
- 1. symptom
tiny black flies lift off every time you water
they hover around your plants and occasionally your face. they're not fruit flies (those prefer the kitchen) — fungus gnats are smaller, darker, and live in your plant pots. the flies are annoying; their larvae in the soil are the actual infestation.
- 2. cause
permanently wet topsoil is a gnat nursery
gnats lay eggs in the top 3–5cm of moist soil, larvae feed on fungus and organic matter there, and a new generation flies up every couple of weeks. if you water a little and often, you're running a breeding program.
- 3. the fix
hit both generations for three weeks
adults: yellow sticky traps in every affected pot — they're drawn to the color, and trapped adults lay no eggs. larvae: let the top 5cm of soil dry out completely between waterings; switch to bottom-watering so the surface stays dry while roots still drink. stubborn cases: water once with a BTI (mosquito bites/dunks) solution — a bacteria that kills larvae and nothing else. keep all of it up for three weeks, one full life cycle.
why it always comes back (when it does)
people stop too early. the traps clear the air in days and it feels solved — but the next generation is still chewing through your topsoil. if you quit in week one, you'll meet their grandchildren in week three. the calendar matters more than the product.
prevention is one habit
the same habit that prevents overwatering prevents gnats: let the topsoil dry before watering again. gnats physically can't establish in soil that dries out regularly. new plants from the store are the usual reintroduction route — quarantine them near (not among) the others for two weeks.
people keep asking…
- are fungus gnats harmful to my plants?
- adults are harmless (just irritating). larvae mostly eat fungus and dead matter, but in heavy infestations they nibble fine roots — seedlings and cuttings are the only real casualties.
- how do i tell fungus gnats from fruit flies?
- location and look. fungus gnats are small, slim and black, hover around plant pots and walk on the soil. fruit flies are rounder, browner, and live where the bananas are.
- does cinnamon on the soil get rid of fungus gnats?
- it's a mild antifungal, so it reduces the larvae's food a little — but on its own it won't break the cycle. traps plus dry topsoil work; cinnamon is at best a garnish.
- how long does it take to get rid of fungus gnats?
- about three weeks if you run traps and let the topsoil dry from day one. you'll see fewer flies within days, but stop early and the next generation restarts the clock.
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