Houseplants are wonderful. They look lovely, bring a dose of nature indoors where you need it most, and they purify the air. However, you might notice some unwelcome visitors making your houseplants their home. I’m talking about fungus gnats—those annoying little flies that appear whenever you water your plants. Don’t worry, there are simple—and natural—ways to prevent and get rid of fungus gnats.
What Are They and Where Did They Come From?
Fungus gnats, also sometimes called soil gnats, are small dark insects that resemble fruit flies and infest houseplants. If you have them, you will notice them appear when you disturb the soil or water your plants. Fungus gnats can get into your houseplants when they are left outside, but usually they come straight from the nursery, where they hide in the soil until you bring them home unknowingly. Their larvae eat fungi and plant roots in the soil, which is why they suddenly appear in houseplants when the larvae hatch (after munching on the roots).
Although they don’t do much damage to strong, healthy plants, they can cause yellowing, stunted growth, and even death in seedlings and more fragile plants. Plus, nobody wants a swarm of gnats flying in your face every time you water your houseplants. Yuck.
How to Get Rid of Them
Start by drying out the soil. Fungus gnat larvae need moist soil, so if you let it dry out completely before your next watering, it will get rid of soil gnats that are already there and discourage new ones from laying their eggs.
Spray the top of the soil with a soap-and-water mixture. This will kill the larvae. Do it again in a few days to ensure that it gets all of the larvae.
Replace the top inch of soil with sand or gravel. Fungus gnats only lay their eggs in the top inch of soil, and replacing that top inch with sand or gravel creates a dry environment with no nutrient-rich fungus for them to munch on, so they won’t want to lay their eggs there. Be sure that you dispose of the top layer of soil outdoors somewhere, as the eggs can still hatch and you don’t want to just move your pests from one part of the house to another.
How to Prevent Them
Don’t overwater your houseplants. This is the most important thing for preventing fungus gnats. They love moist environments and the eggs can’t survive in dry soil, so let your soil dry out completely between watering as much as possible. When you do water, water from the bottom, as this will help the topsoil (where the gnats lay their eggs) stay dry while keeping your plant hydrated and happy.
Store extra potting soil in an airtight container. If you keep your potting soil in the bag it comes in, fungus gnats can easily get in and lay their eggs, but the eggs need air to survive so airtight containers like buckets with tight-fitting lids will keep gnat larvae at bay.