How to Get Rid of Fungus Gnats in Houseplants

This guide is for houseplant owners who keep seeing small dark flies around pots, windowsills, or lamps. It walks you through clearing them out without harming your plants, pets, or kids. It also helps you avoid the usual traps: overwatering a plant that is already struggling, or trapping adults while the larvae keep breeding in the soil. If your watering has been on autopilot, a schedule by plant type is worth a look alongside this guide.

Short answer

Fungus gnats breed in damp potting mix, so fix the moisture first. Let the top of the soil dry where the plant allows, clear out decaying debris, and hang yellow sticky cards to catch adults. If larvae are present, drench the soil with a Bti product (Bacillus thuringiensis israelensis) labeled for the job. Bti only kills larvae, so repeat it as the label directs. Plan on several weeks, because the egg-to-adult cycle takes about three to four weeks at normal room temperature (Colorado State University Extension).

Do you actually need to do this?

Not every stray fly needs a full campaign. Washington State University says light infestations may be controlled with sticky traps alone. Larvae can hurt roots, though, and seedlings are the most at risk (Oregon State University Extension).

Signs you should act:

• Adults keep showing up around the same pots week after week.
• You find pale, thin larvae with shiny black heads in the top inch of soil.
• Seedlings are failing, or a plant has yellowing and wilting leaves with no other cause.
• Soil stays wet for days, or water sits in saucers.

Signs you can go lighter:

• You see only a few flies, and the soil dries normally.
• The plant is growing well.

Checklist:

• Look at the soil surface and the top inch for larvae.
• Note which pots stay wet longest.
• Decide which plants tolerate drying and which don't.
• Treat seedlings and any declining plants first.

What you need

• Yellow sticky cards. Get plastic or laminated cards with adhesive, plus stakes or another way to mount them upright.
• A Bti soil-drench product labeled for indoor plants. Gnatrol and Vectobac are named by NC State Extension. Wisconsin Extension lists Gnatrol and Mosquito Bits as homeowner options. Availability varies by area. Colorado State says Bti products marketed for fungus gnat control are generally not sold through retail outlets there. If you can't find one locally, check nurseries or garden centers, and read the label of anything you buy.
• Water and a container for mixing the drench.
• Optional: coarse sand or fine gravel, enough for a ½ to 1 inch layer on each pot.
• Optional: fresh, well-draining potting mix if you need to repot a plant, and a soil moisture meter.
• Time: about 30–45 minutes for the first round, plus a short check every 5–7 days for the next several weeks.
• Cost: prices vary by product and pot count. Sticky cards and Bti are the main purchases, and sand or gravel is optional.

Step-by-step

Step 1: Check for larvae (10 min)

Scrape the top inch of soil in the wettest pots. Larvae live and pupate within about half an inch of the surface (Virginia Tech Extension). Look for whitish, nearly see-through larvae up to ¼ inch long with shiny black heads. Done right: you know which pots are breeding gnats and which are just visited by adults.

Step 2: Clear debris and empty saucers (5 min)

Remove dead leaves, rotting plant matter, and anything decaying on the soil, in trays, or around the pots. Tip out any water standing in saucers (Clemson Extension). Decaying material and standing water keep the soil damp and the fungi growing, and the larvae eat those fungi. Done right: surfaces are clean and no saucer holds water.

Step 3: Dry the top layer, plant by plant (ongoing)

For plants that tolerate it, let the top 1 to 2 inches of mix dry between waterings (Colorado State University Extension). Wisconsin's guide says to let the top inch dry. If you can't decide, start with the inch and go deeper on plants that clearly tolerate drying. Dry soil kills larvae and removes egg-laying sites. Done right: the surface is dry to the touch before you water again.

Step 4: Hang yellow sticky cards (5 min)

Mount cards vertically on stakes, close to the infested pots, so flying adults hit them (Washington State University). Cards catch adults and show you whether numbers are dropping. They don't touch larvae in the soil. Done right: cards are upright near the pots, and you count catches each week.

Step 5: Add a sand or gravel top layer if you want one (10 min)

Cover the soil with ½ to 1 inch of coarse sand or fine gravel. This keeps the surface drier and makes it less appealing for egg-laying (Wisconsin Extension). It is an extra measure, so skip it if the plant doesn't suit it. Done right: soil is fully covered and the plant's crown is not buried.

Step 6: Drench the soil with Bti (15 min plus soak)

Follow your product's label for amount and method. Some products are mixed with water, left to soak for 30 minutes, then poured onto the soil (Oregon State University Extension). Use enough water to carry the Bti down through the mix to where the larvae are. Bti doesn't affect eggs, pupae, or adults. Don't copy a dose from one product to another, because formulations differ. Done right: soil is evenly moist after the drench, with no water left in the saucer.

Step 7: Repeat every 5–7 days (about 3–4 weeks)

Wisconsin recommends several applications spaced five to seven days apart to catch newly hatched larvae, until the infestation is under control. Eggs hatch in roughly 3–6 days, so one treatment will miss later hatchers. As a practical plan, keep going through at least one full life cycle (three to four weeks) and keep the cards up. Done right: each week's card count is lower than the last.

Step 8: Repot badly infested plants and quarantine newcomers (30+ min)

If a plant is heavily infested and you can't discard it, repot into fresh, well-draining mix to knock down the larvae (Washington State University). The repotting guide covers the method. WSU also says plants with repeated heavy infestations should be discarded. Keep new or infested plants isolated and inspect them for about a month. Done right: infested plants sit apart from healthy ones until they stay clean.

Is it fungus gnats? Quick ID versus fruit flies and shore flies

Fungus gnats are tiny, dark, slender flies about ⅛ inch long. They hang around houseplant soil and rest on the soil surface. Fruit flies and shore flies can look similar at a glance, so the soil check is how you confirm. Scrape the top inch of a damp pot and look for the pale larvae with black heads described in Step 1. Sticky cards near the pots will also show you how many small flies are actually tied to your plants.

Larvae in the soil mean you have fungus gnats. If you see flies but never find larvae, your pots may not be the source. Look for other breeding spots, such as decaying material elsewhere in the room.

Treatment by plant type: dry-out tolerant versus moisture-loving

Dry-down advice only applies to plants that can take it. Clemson says to let soil dry between waterings "for plants that can tolerate it", which covers most houseplants, especially in winter. Let each plant's normal care needs decide how far you go.

Plants that tolerate drying:

• Let the top 1–2 inches dry between waterings.
• Use sticky cards and Bti if larvae are present.
• Add the sand or gravel layer if you like.

Moisture-loving plants:

• Don't impose a dry-out they can't handle. Instead, keep the surface drier without starving the roots.
• Water from the bottom to moisten the roots while the surface stays dry (Wisconsin Extension).
• Add a ½ to 1 inch layer of sand or gravel.
• Use Bti to treat larvae, and keep saucers empty after watering.
• If a plant is heavily infested, repot into fresh, well-draining mix.

Seedlings: larvae can damage seedlings directly, so treat these first. Use sticky cards and follow the Bti label.

What works, what doesn't: home remedies evaluated

Works, with limits:

• Drying the surface. Dry conditions kill larvae and remove egg-laying sites.
• Yellow sticky cards. They catch adults and are enough for light infestations, but they don't reach soil larvae.
• Bti drench. It targets larvae only.
• Coarse sand or fine gravel. A helpful extra layer, not a stand-alone cure.

Unproven, so don't rely on them: cinnamon, apple cider vinegar traps, neem, soap sprays, matchsticks, and hydrogen peroxide drenches. University extension guidance centers on dry-down, cards, Bti, and sand or gravel. Don't swap an unproven remedy in for larval control. If you try one anyway, keep the proven steps going alongside it.

Pet and child safety for each treatment

Don't assume a product is safe just because it is biological or common. Read the label for storage, application, and access restrictions on anything you use.

• Watering changes and clearing debris: no product involved.
• Sticky cards: mount them on stakes as directed. If a child or pet could reach one, move it or skip it.
• Sand or gravel layer: a physical layer rather than a chemical. Check that pets can't dig it out or swallow it.
• Bti: NC State Extension calls Bti products among the "less hazardous" consumer options. Less hazardous still isn't risk-free, so follow the label, keep the product stored as directed, and keep pets and kids away from mixed drench water.
• Other insecticides, peroxide, neem, or diatomaceous earth: follow each label exactly. Check with your vet or a poison-control service before using them around pets.
• Toxic plants: if a pet or child chews a plant or a product, call poison control or your vet right away.

When gnats keep coming back

Look for what is keeping the soil damp or bringing new gnats in.

• Wet conditions: overwatering, water in saucers, and mix that stays soggy. Soil rich in organic matter holds moisture and fungi.
• Incoming plants: gnats can arrive on new plants, on plants moved indoors, or through screens. Quarantine new purchases and returning plants for about a month and inspect them.
• Untreated pots: one untreated infested pot can reseed the others. Treat every pot that has larvae.
• Heavy repeat infestations: discard plants that suffer them repeatedly.

If a plant yellows and wilts despite treatment, check the roots, and a rundown of why leaves turn yellow can help you rule out other causes. If the problem persists after several weeks of consistent treatment, bring a sample to your local extension office.

Common mistakes and why they cause harm

• Only using sticky cards on a heavy infestation. Cards catch adults, but larvae keep developing in the soil and new adults keep emerging.
• Treating once and stopping. Eggs hatch over several days and the life cycle runs three to four weeks, so later larvae survive a single drench.
• Drying out every plant the same way. Moisture-loving plants can suffer if pushed too dry. Match the dry-down to the plant.
• Using one product's dose for another. Formulations differ, and the label is the only reliable dose.
• Leaving water in saucers. Standing water keeps the root zone damp and feeds the fungi that larvae eat.
• Skipping quarantine for new plants. Gnats ride in on new purchases and plants brought in from outdoors.
• Treating adults only when seedlings are at risk. Larvae can damage seedlings, so these need soil treatment early.

What to expect afterward

You won't see instant results. Adults live only seven to ten days, but eggs and larvae keep producing new ones, so catches may stay up for a while. Expect card counts to fall week by week over about three to four weeks of consistent treatment. Keep cards up until the count stays near zero.

Keep watering on a plant-appropriate schedule, with saucers emptied, so the soil doesn't stay wet. Watch for yellowing or wilting leaves, which can signal root damage from larvae. If counts are not dropping after several rounds, check that you treated every infested pot and that nothing damp is breeding more gnats.

Frequently asked questions

How long does it take to get rid of fungus gnats? Plan on three to four weeks at least, because that is how long the egg-to-adult cycle takes at normal room temperature. Keep drying the soil, repeat Bti every 5–7 days, and leave cards up until catches stay near zero.

Do sticky cards alone solve the problem? For light infestations, they may. For heavier ones, they only catch adults. Add soil treatment so larvae don't keep turning into new adults.

Can I use Mosquito Bits or Gnatrol? Wisconsin Extension names both as Bti products homeowners can use against fungus gnat larvae in soil. Follow the label on whichever you choose, since doses differ between formulations.

Should I repot an infested plant? Repotting in fresh, well-draining mix can help when a plant is heavily infested and you can't discard it (Washington State University). For lighter problems, treating in place with drying, cards, and Bti is usually enough. WSU suggests discarding plants that repeatedly get heavy infestations.

How do I keep a moisture-loving plant healthy while cutting gnats? Keep the surface drier without drying the whole pot: water from the bottom and add a sand or gravel layer. Empty saucers after watering and treat larvae with Bti if present.

How far should the soil dry out? Colorado State says the top 1–2 inches, and Wisconsin says the top inch. Neither is a set number of days. Start with the top inch and go deeper only on plants that tolerate drying.

Related guides

• How Often Should You Water Houseplants? A Schedule by Plant Type: Fungus gnats breed in constantly damp soil, so a proper watering schedule is the key to preventing their return.
• How to Repot a Plant Without Killing It: Repotting into fresh, dry potting mix is a direct way to remove gnat larvae and eggs from heavily infested soil.
• Why Are Plant Leaves Turning Yellow? 9 Causes and How to Fix Them: Yellowing leaves often accompany overwatering and gnat larvae feeding on roots, helping readers diagnose plant damage.
• Best Low-Light Plants That Actually Survive: Low-light plants often stay wet longer, so this helps readers choose and care for plants less prone to gnat problems.

Next steps

This week, check the wettest pots for larvae, empty every saucer, and hang yellow sticky cards beside the infested plants. If you are also thinking about low-light plants that tolerate drier soil between waterings, keep them in mind for any replacements, then follow the Fungus Gnat Treatment Checklist as you work through each round.