Fungus gnats are the tiny black flies that appear around houseplants and make your home feel like a badly managed produce aisle. The adults are annoying, but the larvae in moist soil are the real problem. They feed on fungus, organic matter, and sometimes tender roots.
Quick Answer
To get rid of fungus gnats, let the top 1 to 2 inches of soil dry out, use yellow sticky traps for adult gnats, and treat the soil larvae with BTI mosquito bits or another larval control. The key is treating adults and larvae at the same time.
How to Identify Fungus Gnats
Fungus gnats are small, dark flies, usually about 1/8 inch long. They look like tiny mosquitoes but are weaker fliers. You will often see them crawl on the soil surface, fly up when you water, or hover near windows.
They are different from fruit flies. Fruit flies usually gather around fruit, drains, or food waste. Fungus gnats stay close to damp potting soil because that is where they lay eggs.
Why Fungus Gnats Show Up
Fungus gnats love consistently moist soil. If you water often, use dense potting mix, keep plants in pots without drainage, or have decaying organic matter on the soil surface, you are basically running a small gnat resort.
They are also a clue that your watering routine may be too wet. If the plant has yellow leaves too, check [why plant leaves turn yellow](/journal/why-are-my-plant-leaves-turning-yellow).
Step 1: Let the Top Soil Dry
The simplest control is dryness. Fungus gnat larvae need moisture near the soil surface. Let the top 1 to 2 inches dry before watering again. For plants that can tolerate it, extend the dry period a little longer.
Do not dry out moisture-loving plants completely. The goal is to make the egg-laying zone less comfortable, not punish the roots.
Step 2: Use Yellow Sticky Traps
Yellow sticky traps catch adult gnats before they lay more eggs. Place them close to the soil surface, not across the room like decorative modern art. Replace them when they are covered or dusty.
Traps alone will not solve the problem because they do not kill larvae. They are a monitoring tool and an adult-control tool.
Step 3: Treat Larvae with BTI
BTI, commonly sold as mosquito bits or mosquito dunks, targets larvae and is widely used for fungus gnat control. Soak the bits in water according to the product directions, then water the affected plants with the treated water.
Repeat weekly for several weeks. Fungus gnats have a life cycle, so one treatment may not catch every generation.
Step 4: Improve Drainage
Dense, soggy soil keeps the problem alive. If the potting mix stays wet for a week or more, consider adding perlite, bark, or pumice. Make sure the pot has drainage holes and never let the plant sit in standing water.
Bottom watering can help because it keeps the top layer drier while still hydrating roots from below.
Step 5: Clean the Soil Surface
Remove dead leaves, fallen petals, and decaying debris from the pot. Fungus gnats feed on organic decay, so do not give them a buffet.
If the infestation is heavy, replace the top inch of potting mix with fresh, dry mix after treatment.
What Not to Do
Do not spray random insecticide into the air and call it plant care. Do not keep watering daily. Do not ignore the larvae. Do not cover every plant with sand unless the plant can tolerate the change in soil airflow and moisture behavior.
How Long Does It Take?
Most fungus gnat infestations improve within two to four weeks if you treat both adults and larvae. If they keep returning, the soil is staying too wet or untreated plants nearby are acting as a backup population.
Bottom Line
Fungus gnats are not a sign that you are cursed. They are usually a sign of wet soil. Dry the top layer, trap adults, treat larvae, and improve drainage. Do all four at once and the population should collapse.