If you’ve seen little black flies dancing above your houseplants, you’re dealing with fungus gnats. Their larvae thrive in moist, moldy soil—so if you only swat the adults, they’ll be back in a week. Below is a three‑step plan that cuts off the gnats and the moldy buffet they feed on.
Break the Cycle in 3 Steps
Step 1 – Trap & Kill Adult Gnats
Stick a yellow sticky card in each affected pot. Replace when covered. No adults → no new eggs.
Step 2 – Dry & Treat the Soil Surface
- Scoop: Remove the top 1 cm of moldy soil.
- Dry: Let the mix reach the “finger‑test dry” stage.
- Treat: Dust with cinnamon or top‑dress with a thin layer of sand—larvae can’t wriggle through.
Step 3 – Water Smart + Boost Airflow
Water only when the top inch is dry, and aim a small fan past the foliage for at least part of the day. Consistent dryness breaks the gnat life‑cycle and starves mold spores.
When You Might Need to Repot
If larvae persist after two drying cycles, or roots appear brown and mushy, re-pot into fresh, better‑draining mix and toss the old soil outdoors.
Fungus Gnat FAQ
Are fungus gnats harmful to plants?
In small numbers, larvae mostly eat decaying matter. Huge populations can chew fine roots and stunt growth.
Will hydrogen peroxide kill larvae?
A one‑off 1 % H2O2 drench can kill larvae, but it also disrupts soil microbes. Use only if sticky traps + drying fail.
Can I use mosquito bits?
Yes: soak Bacillus thuringiensis israelensis (BTI) bits in water and drench the soil. BTI targets larvae without harming pets.
Still seeing white fuzz? Jump to our full mold causes guide or learn 10 habits that prevent mold for good.