Get Rid of Fungus Gnats on Houseplants

Fungus gnats look like fruit flies hovering around your fiddle leaf fig, and they signal one thing: your soil is staying too wet. These tiny black flies don't damage plants directly, but their larvae feed on organic matter and root hairs in consistently moist potting mix, and a heavy infestation can stress young plants or fresh cuttings. The adults are mostly annoying—they'll fly into your coffee and land on your laptop screen—but they breed fast, turning one or two flies into dozens within weeks. The good news is fungus gnats are easy to eliminate once you understand their lifecycle. Adults live about a week, but females lay up to 300 eggs in moist soil during that time. Those eggs hatch into tiny larvae that feed for two weeks before emerging as new adults, and the cycle continues as long as the soil stays damp. Break that cycle by drying out the soil and creating hostile surface conditions, and your gnat problem disappears in two to three weeks. No pesticides, no repotting, just adjustments to watering habits and a few physical barriers.

1. Cut Off Their Water Supply. Fungus gnat larvae need moisture to survive, so your first move is cutting off their water supply. Let the top two to three inches of soil dry completely before watering again—stick your finger in to check. For most houseplants, this means extending your watering schedule by several days or even a week. Plants in terracotta pots will dry faster than those in plastic or ceramic.
2. Catch the Adults First. Place small yellow sticky traps on stakes in the soil or hang them just above the pot. Adult fungus gnats are strongly attracted to yellow and will fly directly into the traps. This won't solve the problem alone since it doesn't kill larvae, but it reduces the breeding population and gives you a visual gauge of how bad the infestation is. Replace traps when they're covered in gnats or lose their stickiness.
3. Build a Dry Defense Layer. Pour a half-inch layer of coarse sand or food-grade diatomaceous earth across the top of the soil in each pot. This dry barrier prevents adult gnats from laying eggs in the soil and kills any larvae trying to emerge. Sand is cheaper and easier to find; diatomaceous earth has sharper edges that physically damage soft-bodied insects. Either works, but sand looks cleaner and won't blow around.
4. Switch to Bottom-Up Hydration. When you do water again, set pots in a tray of water and let the soil absorb moisture from the drainage holes. This keeps the top layer of soil dry, which discourages egg-laying and makes the environment inhospitable for larvae. Bottom watering also prevents you from accidentally rewetting the sand or diatomaceous earth barrier. Leave pots in the tray for 20 to 30 minutes, then remove and let excess water drain.
5. Eliminate the Larvae Remaining. Mix one part 3% hydrogen peroxide with four parts water and pour it through the soil until it drains from the bottom. The peroxide kills larvae and eggs on contact by releasing oxygen, then breaks down into water. It won't harm plant roots at this dilution. Use this as a one-time treatment after you've implemented the other steps—it's insurance, not a primary control method.
6. Eliminate All Water Reservoirs. Empty saucers and drip trays under your pots every time you water. Standing water keeps the bottom of the soil saturated and creates breeding sites for gnats. If you use decorative cache pots, pull the grow pot out after watering and dump any collected water. This is basic hygiene, but it's where most people slip up and reintroduce the problem.
7. Contain the Infestation Zone. If one plant has a severe infestation, move it away from your other houseplants while you treat it. Fungus gnats are weak fliers but they'll migrate to nearby pots with moist soil. Keep treated plants separate for two to three weeks—one full gnat lifecycle—and monitor sticky traps. When you see no new gnats for a week, it's safe to return the plant to your collection.
8. Reset Your Watering Rhythm. Once the gnats are gone, keep them gone by watering less frequently and more deeply. Let soil dry out between waterings instead of keeping it constantly moist. Most houseplants prefer this anyway—wet feet cause more problems than fungus gnats. If a plant truly needs consistent moisture, top-dress with sand permanently and stay vigilant with sticky traps.