Fungus gnats can be controlled by drying the soil, trapping adults, and killing larvae in the potting mix; the key is breaking their life cycle over several weeks.

What fungus gnats are

  • Fungus gnats are tiny dark flies that lay eggs in moist potting soil and whose larvae feed on fungi and decaying organic matter, sometimes nibbling on fine roots.
  • They are more of an annoyance for established plants but can stunt seedlings and delicate houseplants if the infestation is heavy.

Quick win steps (today and this week)

  • Let the top 1–2 inches of soil dry out before watering, since larvae cannot survive well in drier conditions and this slows their life cycle.
  • Move heavily infested plants away from others and add yellow sticky traps near the soil surface to catch swarming adults quickly.
  • Reduce bottom-watering and constantly soggy saucers, which create the consistently wet environment fungus gnats love.

Targeting adults (the flying gnats)

  • Use yellow sticky traps pushed into the soil or hung just above it; adults are attracted to the color and get stuck, preventing them from laying more eggs.
  • Simple vinegar traps (a small cup of apple cider vinegar with a drop of dish soap and plastic wrap with holes) can lure and drown some adults around plant shelves.
  • Avoid spraying harsh synthetic insecticides indoors just for adult gnats, since they are relatively harmless to humans and easier to manage with physical traps.

Killing larvae in the soil

  • Drench the soil with a mix of 1 part 3% hydrogen peroxide to 4 parts water to fizz through the potting mix and kill larvae, repeating when you water until activity drops.
  • Use products containing the bacterium Bacillus thuringiensis israelensis (BTI), sold as Mosquito Bits or similar; sprinkle on the soil or make a “tea” to water with, which kills larvae but is safe for plants and pets when used as directed.
  • Some growers also layer coarse sand or a gnat barrier material on top of the soil to create a dry, abrasive surface that larvae and emerging adults struggle to pass through.

Prevention and long‑term control

  • Switch to a well-draining potting mix and pots with drainage holes, and avoid overwatering, especially in low light or during winter when plants use less water.
  • Quarantine new plants for a couple of weeks, using sticky traps and lighter watering to catch any hidden fungus gnat populations before they spread.
  • Periodically use mild biological controls such as BTI drenches or natural fungicidal approaches like chamomile tea and cinnamon to keep soil less hospitable to gnats’ food sources.

TL;DR: Break the cycle: dry the top soil, trap adults with yellow sticky cards, and repeatedly treat the potting mix (hydrogen peroxide or BTI) over several waterings until no new gnats appear.

Information gathered from public forums or data available on the internet and portrayed here.