Does Cinnamon Work Against Fungus Gnats? What Experts Recommend

Fungus gnats—pesky little insects that infest your houseplants—can be difficult to control once they’re established. To combat them, home gardeners have tried everything from bottom watering to sticky traps to home remedies that spread via social media. We wondered about one such viral remedy: Can you really get rid of fungus gnats with cinnamon?

We found out what the experts had to say about this too-good-to-be-true houseplant hack.

Where Do Fungus Gnats Come From?

Fungus gnats can hitch a ride into your home via a bag of potting mix or in the soil of a new houseplant. Once established, they multiply quickly and can spread throughout your houseplant collection.

“Gnats love our houseplants because the potting mix provides an ideal habitat for them to raise their young,” says Justin Hancock, horticulturist with plant nursery 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.”

Aside from the annoyance of adult fungus gnats buzzing around your space, a fungus gnat infestation can lead to problems with your plants, too. Their larvae can feed on roots, harming plant health and stunting growth in severe cases.

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Does Cinnamon Keep Fungus Gnats Away? 

No—but the idea that cinnamon could provide a natural method for controlling fungus gnats has some basis in reality.

The essential oils in cinnamon possess antimicrobial properties that could be used to control fungi in the soil or combat fungal diseases in plants.

“Unfortunately, you can’t count on cinnamon on or in the potting mix to help control fungus gnats,” Hancock says. “Many types of cinnamon, but not all, contain antifungal compounds, so while they may potentially help prevent the growth of fungi, there’s no reason or evidence to suggest cinnamon should affect this insect.”

Can Cinnamon Prevent Mold Growth on Soil?

Because fungus gnat larvae feed on, well, fungi, could controlling the growth of fungi or mold in or on your plants’ soil get rid of fungus gnats?

“You may find that using cinnamon can stop mold from growing further, but there’s no scientific evidence that antifungal compounds are released in a form that can affect soil-dwelling fungi,” Hancock says. “That said, their presence can potentially be a sign that the potting mix is staying too wet, which could lead to roots drowning, dying, and rotting.”

If you’re seeing molds or mushrooms growing among your houseplants, Hancock recommends avoiding overwatering or using a small fan to generate airflow.

Which Fungus Gnat Treatments Actually Work?

Hancock recommends these strategies for treating a fungus gnat problem in your home:

• Apply a layer of sand to the soil: “Since fungus gnat larvae, which look like small white worms, feed and grow in moist potting mix, creating a barrier that prevents the adults from laying eggs in the potting mix can be effective,” he says. “Spreading an inch or two of sand over the soil is one of the easiest ways to make this barrier.”
• Change your watering habits: “Depending on the plant variety, reducing your watering schedule and watering from the bottom so that the top layer of soil in your plant stays pretty dry can make it uninhabitable,” says Hancock. However, allowing the soil to fully dry out between waterings may not be the best choice for moisture-loving plants like ferns, peace lilies, and fittonia.
• Monitor progress with sticky traps: These bright, sticky cards you put in your plants’ soil can halt a small number of adult gnats from reproducing. However, for bigger infestations, Hancock recommends using them to measure fungus gnat populations and track your progress while using other strategies.
• Treat soil with Bti: “If you want to use nature to fight the gnats for you, you can turn to a naturally occurring bacterium called Bacillus thuringiensis israelensis, or Bti,” Hancock says. “Regularly using this in your water as you water your plants builds up a population of this bacterium in the soil that will kill larvae.”
• Use beneficial nematodes: “Another biological control that can be effective is S. feltiae nematodes. These nearly microscopic organisms also go after fungus gnat larvae and are applied by adding to the water you use on your plants,” he says.

How Can You Keep Fungus Gnats From Coming Back?

Once you’ve conquered your fungus gnat problem, take special care when bringing home new plants to prevent a recurrence.

“If you’ve eliminated fungus gnats in your home, you won’t see a return unless you introduce new fungus gnats into your home via a new plant,” Hancock says. “If you purchase a new plant, quarantine it so you can be sure there are no fungus gnats, or treat any existing fungus gnats before moving it with your other plants.”