How to Treat Fungus Gnats (Without Losing Your Mind)
If you’ve ever watered a houseplant and watched tiny bugs come flying out of the soil, chances are you’ve met the infamous fungus gnat. Don’t worry—they’re more annoying than harmful. But I know how frustrating they can be. Here’s how to get rid of them and keep them from coming back.
What Are Fungus Gnats?
Fungus gnats are tiny black flies (about the size of a fruit fly) that lay eggs in damp potting soil. Their larvae feed on fungi and organic matter in the soil—and sometimes fine root hairs, especially in seedlings. You’ll usually see the adults flying around the soil surface or near windows.
The good news: They don’t bite, and they rarely cause lasting damage to mature plants.
Why Do I Have Them?
Fungus gnats thrive in:
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Moist potting soil (especially when it stays damp too long)
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Organic-rich media like peat moss or compost
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Poor drainage or overwatering
Basically, they love what your plants love—but a little too much of it.
How to Treat Fungus Gnats
1. Let the Soil Dry Out
Most fungus gnat larvae live in the top 1–2 inches of soil.
Letting the top layer dry between watering interrupts their life cycle.
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Water less often or from the bottom if possible
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Remove decorative moss or rocks if they’re trapping moisture
2. Use Sticky Traps
Yellow sticky traps are your best friend here—they catch the flying adults and reduce the number of new eggs being laid.
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Stick one right into the soil of infested plants
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Replace every few days or as needed
3. Use Mosquito Bits
Mosquito bits are a biological control intended to kill mosquito larvae, but they work on fungus gnat larvae as well! What exactly are mosquito bits? Mosquito bits are corn covered in Bacillus thurengiensis (BT). To treat kill fungus gnat larvae, make a mosquito bit tea. Place mosquito bits in you watering can, let it "steep" overnight, then water as usual.
4. Top with Sand or Grit
A layer of coarse sand or horticultural grit on top of the soil can block adult gnats from laying eggs and help dry the surface faster.
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Aim for about 1/2 inch deep
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Works best when paired with reduced watering
5. Repot if Necessary
If the infestation is persistent, or the soil smells sour or stays wet too long, it may be best to repot entirely.
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Use fresh, sterile potting mix
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Clean the pot thoroughly before reusing
How to Prevent Fungus Gnats
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Don’t overwater—most indoor plants prefer to dry out a bit between watering
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Use well-draining potting mix and pots with drainage holes
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Keep new plants quarantined for a couple weeks to avoid bringing gnats in
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Use sticky traps regularly as an early warning system
In the Shop
At Rooted Living, we carry Fungus Gnat Treatment Kits, which include 5 yellow sticky traps and mosquito bits,—just enough o handle a small infestation. Plus we’re always happy to talk through your plant care questions when you're in the shop.
Want to learn more? Check out this article from the UW-Madison Extension.
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