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Bug Series: How to Deal With Fungus Gnats

Talk about tiny! Fungas Gnats! These itty-bitty little black flies, love wet habitats. We don’t notice them often outside in the open environment, but they are common household pests for our house plants.

Why they’re good:

Fungus gnats actually serve an important purpose in the greater ecosystem. They don’t harm our plants but rather, live symbiotically with them. The feeding habits of gnats aid in the decomposition of different materials in the soil, creating readily available nutrients for microbes and plants. They also help to regulate nutrients among plant populations by transporting nutrients between plants. For the most part, these functions are useful in an outdoor, natural setting.

When they’re bad:

In an artificial setting, like your home, on the other hand, your houseplants don’t necessarily need ‘nutrient regulation.’ Instead, the presence of these little flies can become a significant nuisance (who wants little flies all over their house?), and they can even begin to feed on other available material, like fruit, in your home. In unique situations, fungus gnats can also inadvertently carry an existing (and contagious) plant disease from one plant to the next. For the most part, your plants might not be bothered by Fungus gnats, but we are willing to bet that you are.

Where & When you’ll find them:

Soil decomposition happens more readily in a moist environment, providing the perfect environment for gnats. They will lay their eggs in the wet soil, which hatch within about a week. After about a week as tiny (almost microscopic) larvae hiding in the soil, they mature into adult flies, which survive for approx. another week. Outdoors, we find these flies most readily during wet seasons in the spring and summer, but inside, fungus gnats can thrive any time of year.

These gnats are extremely common here, and most fungus gnats are introduced to a home through open doors, windows, new houseplants, or indoor/outdoor pets. It’s practically impossible to avoid ever having fungus gnats, but they are easier to control than most people realize! We’ll get to that in a minute.

How They Impact Your Plants:

For the most part, gnats don’t really affect your plants and they won’t cause damage or stress to your leafy friends. However, if you have a plant that is already battling a fungus or other spreadable disease, a subsequent fungus gnat infestation can mean that travelling gnats can inadvertently spread that disease to other plants.

Identifying Fungus Gnats

You might be able to see tiny clear or white eggs tucked into surface crevices in the soil (using a magnifier), but for the most part, you’ll notice fungus gnats once they are adults. Most of the population will hang out on the surface of the soil, quickly fluttering up into the air when the soil is disturbed or a plant pot is bumped. You might find them resting on the leaves of a plant, in sink drains, window sills, garbages, or fruit bowls around your house. If you’ve got gnats, they are likely laying eggs in the soil of a potted houseplant – but if the infestation has spread, they may also be finding other areas of decay to lay eggs (garbage receptacles are common as well).

How To Deal With Fungus Gnats

Sticky Sticks: Good ol’ fashioned insect traps! These are surprisingly effective for dealing with gnats. These sticky traps can be positioned in any houseplant pot (or hung in other problem areas), to attract and catch adult gnats. Since fungus gnats have about a 3-4 week lifecycle, these traps are most effective when they are used consistently for 4-6 weeks (change as needed) in order to catch all surviving generations as they hatch.

Let the Soil Dry Out: Since gnats thrive in a wet environment, the best thing you can do is let the soil dry out as much as possible without putting your plants in jeopardy. One great little hack for watering ‘from the bottom’ is to fill a tray with rocks and water, set your plant pot on top (if it has drainage holes), and let the soil wick up water as needed. Gnats that are living on the surface of the soil won’t be able to benefit as much from the moisture content.

Bacillus Thuringiensis: That mouthful of vowels is the name of a naturally-occurring, beneficial bacteria that kills many types of larvae, including fungus gnats (also mosquitos and thrips…). You can find this active ingredient in some organic gardening products, including Mosquito Dunks. This product is listed as a specific remedy for mosquito problems, but a lot of plant communities agree that, when added to your watering can, it’s useful tool for preventing household fungus gnat invasions.

What About Other Bugs?

Check out our full bug series here, and follow us on Facebook to get notified as we release new articles in the series!

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Andrea Heembrock
Andrea works as Anything Grows Head of Marketing and Team Builder, and like everyone else at the store, she loves plants! Though she has many years of experience with plants, she gains a great deal of knowledge from her husband, Ty, who has been in the gardening industry for over two decades.