Skip to content
Anchor Pest Services logo
(603) 785-0118
Fungus Gnat — species photo
Daniel Brady · NH-Licensed Pesticide Applicator · License #782664

How to Get Rid of Fungus Gnats

DIY-friendly
To get rid of fungus gnats, let the top one to two inches of houseplant soil dry out between waterings — this is the root cause, since gnats breed in consistently moist soil, not in the air. For a persistent infestation, apply a Bti (Bacillus thuringiensis israelensis) soil drench: it's a naturally occurring bacterium that, once ingested by fungus gnat larvae, kills them specifically without harming people, pets, or beneficial insects, and it's sold as "mosquito bits/dunks" steeped in water to make a soil-drench "tea." Yellow sticky cards catch and help monitor the adults while the soil treatment works on the larvae. Spraying the adults you see does nothing about the larvae still developing in the soil — you have to treat where they're actually breeding.

At a glance

  • Difficulty: Beginner
  • Time: Ongoing watering-habit change; a Bti drench cycle takes 1-2 weeks
  • Cost: Low — yellow sticky cards and a Bti product
  • Success: High with consistent watering changes and, if needed, a Bti drench
The honest answer

Can you DIY Fungus Gnat?

The verdict on Fungus Gnat DIY

DIY-friendlyBeginner

A beginner-friendly DIY — the fix is a soil drench, not a surface spray.

Fungus gnats breed in the moist top layer of overwatered houseplant soil, not in the air around your plants. That means the fix targets the soil, not the visible adults: let the top inch or two of soil dry between waterings, and for persistent cases, apply a Bti (Bacillus thuringiensis israelensis) soil drench that kills larvae with high efficacy and no toxicity to people or pets. This is the cluster's best example of a biological control that genuinely works — no pest license needed.

The playbook

The 5 DIY methods — honestly graded

Every approach graded for this species, in IPM order — prevention first, chemistry late. Pick a method to see how it works, the steps, and what it actually takes.

Prevention / Exclusion

Works well

Drying the soil surface is the root-cause fix — most cases resolve with this alone.

Fungus gnat larvae need consistently moist soil to survive. Letting the top layer dry between waterings removes the conditions they depend on.

Best for: Every case — this alone resolves most mild infestations

  1. Let the top 1-2 inches dry between waterings

    Check soil moisture with a finger or a moisture meter before watering, and wait until the top layer is dry.

    Tip
    Bottom-watering (setting the pot in a water tray) keeps the surface drier than top-watering.

  2. Improve drainage

    Make sure pots have drainage holes and aren't sitting in standing water in a saucer.

  3. Top-dress with coarse sand or grit

    A layer of coarse sand or grit on top of the soil deters adult gnats from laying eggs there.

Tools & materials

Moisture meter (optional)Coarse sand or grit
Before you start
Continuing to overwater re-invites egg-laying even after you treat an active infestation.
Reality check

Why DIY falls short here

Not scare tactics — the specific, proportionate reasons a home attempt can stall for this species.

Killing adults only

Larvae in the soil keep developing and emerging as new adults regardless of how many flying gnats you catch or spray — you have to treat the soil.

Overwatering continues

Moist soil re-invites egg-laying even after a successful Bti treatment, so the watering habit change has to stick, not just the one-time treatment.

Straight talk

How risky is it, really?

An honest read — most nuisance species are genuinely low risk, and we say so.

Low risk

Fungus gnats are a houseplant nuisance. Adults don't bite and pose negligible human disease risk; the main concern is cosmetic or, in heavy infestations, some root damage to seedlings.

  • Seedling or plant root damage in heavy infestationsOccasional

    Larvae can feed on fine roots when populations are large, mostly affecting seedlings and cuttings

    EPA / Summit Chemical

  • Human bites or diseaseRare

    None documented — fungus gnats pose no meaningful human health risk

    EPA / Summit Chemical

When to call a pro

Fungus Gnats Everywhere in Winter?

If soil-drying and a Bti drench aren't enough, there may be a broader moisture issue. Anchor Pest Services offers full inspections across southern and central New Hampshire. Family-owned since 2017, NH license #782664.

Call a pro when…

  • Gnats persist despite soil-drying and a Bti drench across all affected plants
  • You suspect a source outside your houseplants, like a damp crawlspace
  • A large plant collection makes tracking down every source impractical alone

General Pest Control

Fungus gnats are almost always a DIY-solvable houseplant problem. A pro is rarely needed, but general pest control can help if gnats seem to be coming from somewhere beyond your houseplants, like a crawlspace with persistent moisture.

Get a Free inspection(603) 785-0118

Keep them out

  • Let soil dry between waterings — the single most important habit change
  • Use well-draining soil and pots with drainage holes
  • Quarantine and inspect new plants before adding them to your collection
New Hampshire context

Fungus gnats in New Hampshire homes

Fungus gnats are a year-round indoor houseplant issue in NH, but they often become more noticeable in winter, when homes are sealed up, humidity drops, and residents tend to overwater plants trying to compensate. Adjusting watering frequency for the season is often enough to prevent a recurring problem.

Peak season

Winter, tied to indoor heating season and overwatering habits

Before you treat

Make sure it's a Fungus Gnat

Two quick detours worth taking — confirm the ID, then learn what drew it in so it doesn't come back.

Not sure it's this?

Identify Fungus Gnat in the Pest Library

Why is it here?

What actually attracts Fungus Gnat

Common questions

Frequently asked

Sources & further reading(3)
  1. [1]
    EPA — Bti for Mosquito Control

    Bti mechanism, safety profile, registration status

    govverified 2026-07-13
  2. [2]
    Summit Chemical — Kill Fungus Gnats on Houseplants with Bti

    Bti soil-drench application, reapplication schedule

    industryverified 2026-07-13
  3. [3]
    CDC — Mosquito Control: Larvicides

    Bti larvicide mechanism confirmation

    govverified 2026-07-13

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

Verify license

Last updated July 2026

More in Flies & Gnats

Other species you can tackle

Same category — the dot shows each one's DIY verdict at a glance (green = friendly, amber = doable with care, red = call a pro).

Professional Pest Control

Fungus Gnats Everywhere in Winter?

If soil-drying and a Bti drench aren't enough, there may be a broader moisture issue. Anchor Pest Services offers full inspections across southern and central New Hampshire. Family-owned since 2017, NH license #782664.

Get a Free inspection(603) 785-0118
  • NH-licensed applicators (#782664)
  • Free inspection — same-day service across southern NH

NH License #782664 · No obligation · We answer in person

Keep Exploring

Your next step

Call (603) 785-0118Get an Inspection