Fungus Gnats vs Fruit Flies

How to Identify These Annoying Little Gnats

By Ava Green

Do you have tiny flies buzzing around your home and have no idea where they came from? Before you can get rid of them, you need to know what you're dealing with. Most people assume they're fruit flies, but there's a good chance they're not.

There are three common culprits: 

• Drain flies breed in moist drains. Keep drains closed when not in use.
• Fruit flies hover around overripe produce.
• Fungus gnats, the most commonly misidentified of the three, love the damp soil in your houseplants, and they're the ones most likely buzzing around the house.

Fungus Gnats are Probably Already in Your Home

Every time you bring a plant indoors,  whether it's brand new or returning after a summer outside, there's a very good chance it's carrying fungus gnat eggs in its soil. When you purchase bagged soil, it will often contain fungus gnat eggs as well. They're small, they're sneaky, and here's the most important thing to know: they multiply fast. Left unmanaged, a handful of gnats can turn into hundreds within weeks.

What Makes Fungus Gnats Thrive?

Fungus gnats love warm, moist conditions and organic material, like your potting soil. Adult gnats lay eggs in damp soil, which gives their larvae everything they need to develop.

The good news? Once you understand what they need to survive, stopping them is very easy and straightforward.

7 Proven Ways to Get Rid of Fungus Gnats 

1. Quarantine any new or returning plants for 4 weeks. This single step prevents gnats from spreading to your other houseplants while you treat the soil.

2. Use yellow sticky traps. These inexpensive traps attract and catch adult gnats before they can lay more eggs. Place one directly into the soil near your plant. Putting a sticky trap in a planter, whether it’s a new plant or one you’ve had a while, is also a good way to monitor whether or not you have pests in your plants.

3. Let the top inch of soil dry out completely between waterings. Fungus gnats need moist soil to lay their eggs. Deny them that, and you deny them a future. To test whether the soil has dried out, poke one of your fingers in it about an inch to check for moisture.

4. Cover the soil surface with coarse sand or vermiculite. A layer of sharp, gritty material on top of the soil is uninviting to egg-laying adult gnats. Make sure to use coarse sand, fine sand won't do the trick.

5. Switch to bottom watering. This is the best watering method for a number of reasons, including discouraging fungus gnats. Fill a tub or sink one-quarter full and set your pot in it for about 30 minutes allowing water to be absorbed into the soil via the drainage hole in the pot. When the soil and roots absorb water from below, it keeps the top layer of soil, where gnats want to lay their eggs, dry and uninviting. Make sure the water level covers no more than one-third of the pot, not the entire pot.

6. Try Mosquito Dunks (the secret weapon most gardeners don't know about). These contain BTI, a naturally occurring bacterium that is harmless to humans, pets, and plants, but lethal to fungus gnat larvae. Simply follow the package instructions and water your plants as normal. Water activates mosquito dunks.

7. Water with diluted hydrogen peroxide once a week. Mix one part 3% hydrogen peroxide with four parts water (so ¼ cup peroxide to 1 cup water). Apply this solution once a week for three weeks, and let the soil surface dry out between each application. It kills larvae on contact. Don't overdo it though.  Too much, too often can damage roots.

Don’t Forget Your Fruit Bowl: Try This Banana Trick

Fungus gnats aren't just plant pests, they're also drawn to fruit, especially bananas. The stem end of a bunch of bananas is a prime spot for gnat eggs. The fix is simple: as soon as you get home from the grocery store, rinse your bananas under lukewarm running water and give the stem a gentle scrub with a soft brush. It takes about a minute and can prevent a whole new infestation before it starts.

The Bottom Line

Fungus gnats feel impossible to eliminate because most people only address the adults they can see and not the larvae multiplying in damp soil. Use these tips in combination for the best results, and remember: even a fresh bag of potting soil can carry eggs, so treat new soil with BTI or a hydrogen peroxide solution before use.

Stick with it for a few weeks and your home and your plants will be gnat-free.