How to Get Rid of Fungus Gnats in Houseplants

If you've spotted tiny black flies hovering around your plant's soil or bumping into your window, you've probably got fungus gnats. They're one of the most common houseplant nuisances, and the good news is they're usually easier to deal with than they seem once you understand what's actually going on in the soil.

Quick Answer

Fungus gnats live and breed in damp potting soil. To get them under control: let the soil surface dry out appropriately between waterings, set out yellow sticky traps to catch the adults, and use Bti (a soil-safe biological larvicide) to target the larvae living in the soil. Most cases improve within a few weeks of consistent action — it's rarely an overnight fix, but it is manageable.

What Are Fungus Gnats (and Are They Harmful?)

Fungus gnats are small, dark, mosquito-like flies, usually about 1/8 inch long, that hover near the soil surface or fly up when the pot is disturbed. Their larvae live in the top layer of moist potting soil, where they feed on fungi, organic matter, and sometimes fine plant roots.

Fungus Gnats vs. Fruit Flies

Not every tiny fly around your plants is a fungus gnat — it's worth checking before you start treating for the wrong pest.

• Fungus gnats are slender, dark, and have long legs and a mosquito-like shape. You'll usually see them near the soil, not around your fruit bowl.
• Fruit flies are rounder, tan or brown, with reddish eyes, and are drawn to ripening fruit, drains, and trash — not soil.

If your "flies" are hanging around a fruit bowl or kitchen counter more than your plant pots, fruit flies (or drain flies) are the more likely culprit, and the fix is different.

Do Fungus Gnats Hurt Houseplants?

This is where it helps to separate adults from larvae. Adult fungus gnats are mostly a nuisance — they don't bite, and they generally don't feed on or damage the plant itself. The larvae are a different story: they live in the soil and can feed on fine roots and organic matter. In small numbers, this usually isn't a serious problem for an otherwise healthy, established plant. In larger numbers, or on seedlings, cuttings, or already-stressed plants, larval feeding can contribute to root damage and slower growth.

In short: seeing a few gnats doesn't mean your plant is dying. It's a signal to adjust your watering and get ahead of the population before it grows.

Why You Have Fungus Gnats (The Real Cause)

Fungus gnats need consistently moist soil to complete their life cycle. If the top layer of soil rarely dries out, you're giving them exactly what they need to keep breeding. This is why gnats show up so often after overwatering, using a pot without drainage, or keeping saucers full of standing water. If you're not sure whether your watering habits are part of the problem, our guide on overwatering vs. underwatering walks through how to tell.

Gnats can also hitchhike in on new potting soil or a newly purchased plant, which is why it's worth checking new arrivals before placing them next to your existing collection.

The 3-Step Plan to Get Fungus Gnats Under Control

This isn't a guaranteed one-week fix — but consistently doing these three things is the most effective, beginner-friendly approach, and most people see real improvement within a few weeks.

Step 1: Let the Soil Surface Dry Out Appropriately

This is the most important step, because it removes the environment gnats need to breed. Before watering, check the top inch or two of soil and only water once it's dried out to the level that plant actually needs (some plants want the whole pot to dry out; others don't — this step should follow your plant's normal watering needs, not force every plant into the same schedule). Adjust for pots without drainage holes, which tend to stay wet longer than necessary.

Step 2: Catch the Adults with Yellow Sticky Traps

Yellow sticky traps, placed just above the soil surface, attract and catch adult fungus gnats as they emerge and fly around. This won't reach the larvae already in the soil, but it does two useful things: it reduces the adult population that's laying new eggs, and it gives you a simple way to monitor whether your other steps are working — fewer gnats stuck to the trap over time is a good sign.

Step 3: Target the Larvae with Bti

Bti (Bacillus thuringiensis israelensis) is a naturally occurring bacteria sold in some houseplant pest-control products, typically as granules or a soil soak, that specifically targets fungus gnat larvae in the soil without harming the plant when used as directed. It's worth remembering that sticky traps and Bti do different jobs — traps reduce the adults you see flying around, while Bti addresses the larvae actually living in the soil. Using both together, alongside drier watering habits, covers the problem from both ends. Always follow the specific product's label instructions for application and timing.

Quick Reference: Problem → What to Do

What You're Seeing	What It Means	What to Do
Adult gnats flying near soil or plant	Adults have already emerged and are laying eggs	Set out yellow sticky traps
Soil stays wet for several days	Ideal breeding conditions for gnats	Adjust your watering routine
Larvae visible in top soil layer	Active breeding in the pot	Consider a labeled Bti product
Gnats persist after several weeks	Breeding cycle hasn't been fully interrupted	Recheck watering, repeat treatment, consider fresh soil

If They Won't Go Away

If you've been consistent with drying soil, traps, and Bti for a few weeks and still have an active population, a few things are worth checking:

• Recheck every pot, not just the one you first noticed gnats on — they can spread between nearby plants if soil stays damp in more than one pot.
• Check for a saucer holding standing water underneath the pot, which can keep soil wet even if you're watering correctly from the top.
• Consider repotting into fresh, well-draining potting mix, especially if the current soil has been damp for a long time or is dense and slow to dry. Fresh soil also removes any gnat eggs or larvae already established in the old mix.

Common Mistakes That Keep Gnats Coming Back

• Watering on a fixed schedule instead of checking the actual soil moisture first
• Using a decorative pot with no drainage hole, which traps water at the bottom
• Leaving standing water in a saucer after watering
• Only using sticky traps (which catch adults) without also addressing the larvae or the underlying moisture

Does Cinnamon Actually Work?

Cinnamon on the soil surface is a popular home remedy you'll see recommended online, and it does have some natural anti-fungal properties. However, it isn't a reliably proven fungus gnat treatment the way Bti or drying out the soil are, and it's not something extension or horticultural guidance points to as an effective control method on its own. Don't rely on cinnamon as your main treatment; focus on drying the soil appropriately, trapping adults, and targeting larvae.

How to Prevent Fungus Gnats From Coming Back

• Water based on what the soil actually needs, not a fixed calendar
• Use pots with drainage holes and empty saucers after watering
• Choose a well-draining potting mix, especially for moisture-sensitive plants
• Inspect new plants and new bags of soil before bringing them near your existing collection
• Keep an eye on plants that naturally prefer to dry out more, like snake plants — our guide on how often to water a snake plant is a useful example of matching watering to what a specific plant actually needs

It's also worth knowing that root stress from a gnat larvae population, combined with other watering issues, can sometimes show up as yellowing leaves — if you're seeing that alongside gnats, our article on why Monstera leaves turn yellow can help you rule in or out what's actually going on.

FAQ

Do fungus gnats mean my plant is dying?
No. A few fungus gnats around a healthy, established plant is common and rarely a sign of serious trouble. It's a cue to adjust watering, not a reason to panic.

How long does it take to get rid of fungus gnats?
It varies, but plan on several weeks of consistent effort rather than an overnight fix, since you're interrupting an ongoing breeding cycle rather than a one-time problem.

Can fungus gnats spread to my other plants?
Yes, if those plants also have consistently damp soil. They don't damage plants directly by "spreading" like a disease, but they will lay eggs in any pot that offers the same moist conditions.

Is hydrogen peroxide safe to use on all houseplants?
Hydrogen peroxide soil drenches are a home remedy some people use for gnat larvae, but concentration and plant sensitivity matter, and it isn't a universally safe or standardized treatment. If you're considering it, research the specific dilution carefully or stick to a labeled Bti product instead, which is made for this exact purpose.

Does cinnamon really get rid of fungus gnats?
It has mild anti-fungal properties but isn't a proven or reliable standalone treatment. It's fine as a minor addition to your routine, not a replacement for drying out the soil or using Bti.

Final Takeaway

Fungus gnats are common, usually manageable, and rarely a sign your plant is in serious danger. The fix isn't complicated: let the soil dry out appropriately, trap the adults, target the larvae with Bti, and stay consistent for a few weeks. Get the watering habit right, and you'll likely reduce how often they come back.