How to Get Rid of Gnats on Houseplants—and Prevent Them From Coming Back

If you often see small insects flying around your houseplants, it's likely you have a fungus gnat issue. The insects are attracted to the moist soil of plants, which provides them with an ideal habitat for raising their young. While fungus gnats are a nuisance, the adults themselves aren't inherently harmful to your plants—but the larvae they produce are. The insects produce offspring quickly, so it doesn't take long for a population of the gnats to take over. Luckily, getting rid of fungus gnats (and preventing future infestations) is simple when you're armed with the right tips and techniques.

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What Are Fungus Gnats?

Fungus gnats are small, black flying insects that make their home in the moist soil of houseplants, as well as in greenhouse or nursery settings. "They are short-lived but can reproduce quickly, making them a bit of a challenge to eliminate quickly, says Darren Royer, integrated pest management technician at Longwood Gardens. "Their larvae feed widely on organic material in the soil as well as the roots and stems of many plants."

Signs of Fungus Gnats

The most obvious sign that your houseplants are infested with fungus gnats is the appearance of adult gnats. However, the larvae are the real concern. "As the larvae feed on the roots of your plants, they reduce the amount of nutrients that the plant is able to uptake into its foliage," says Royer. "You may notice that your plant has not been growing quite as well or that the leaves have started to yellow."

Where do Fungus Gnats Come From?

Fungus gnats love houseplants because the potting mix provides an ideal habitat for them to raise their young, says Justin Hancock, horticulturist for Costa Farms. "Adult fungus gnats lay their eggs in moist potting mix, the eggs hatch, and the larvae feed on the naturally occurring fungi and organic matter in the potting mix," he says. "The larvae may feed on plant roots if there's already a problem with the roots and they're decaying or the potting mix doesn't contain enough fungi."

Fungus gnats lay their eggs in the soil, which is how they're brought into the home. "Either you bring in a plant that has eggs or larvae in the soil already, or you repot with potting mix that has eggs or larvae in it," says Hancock. Any rip in a bag of potting mix leaves an opening for gnats to lay eggs.

How to Prevent Fungus Gnats

The easiest way to get rid of fungus gnats is by preventing an infestation from happening altogether.

Check for gnat activity when moving plants from outside back into your home for the colder months. "A treatment outdoors will keep the gnats from moving into other plants around your home or greenhouse," says Royer.
When repotting houseplants, check that the potting mix doesn't have larvae by carefully inspecting the bag for signs fungus gnats may have deposited eggs, says Hancock.
Tap the pot a few times when purchasing new plants. "The disturbance should send the adult gnats flying," says Royer. "If gnats are present, you may want to consider finding that plant at a different store."
Quarantine new plants before introducing them to the rest of your collection. "During the quarantine time, you can inspect for pests and diseases without the risk of infecting your existing plants."
Keep the soil from getting too moist by ensuring proper soil drainage and avoiding overwatering.

How to Get Rid of Fungus Gnats

If you have a fungus gnat infestation, there are a few ways you can get rid of the pests and restore your plants back to health.

Stop Overwatering

Fungus gnats love water, so it's important to monitor your watering. "Often times overwatering provides a perfect environment for pests and diseases," says Royer. "Many houseplants prefer to have a break between watering." If you notice fungus gnats buzzing around your plants, consider adjusting your watering schedule.

Use Sticky Traps

Sticky traps, which are available at most garden centers or online, are another effective way to get rid of fungus gnats. "Simply place the cards near your plants per the package's instructions," says Royer.

Make a Trap

Rather than buying traps, make one with apple cider vinegar. "Take a small cup with 1 inch of apple cider vinegar and cover it tightly with plastic wrap," says Royer. "Poke small holes around the top of the wrap. The gnats will be able to enter the holes, but will not be able to exit."

Apply Hydrogen Peroxide

While traps help control the adult population of fungus gnats, you still need to treat the eggs and larvae in the soil. Make a solution by mixing 1 part hydrogen peroxide and 4 parts water, then pour the mixture into the pot, making sure to completely saturate the soil, says Royer.

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