As people who adore plants, we never want to see them suffer at the hand of pests. But we especially don’t want to see pests in our houseplants, because that brings the problem inside our homes—gross! Fungus gnats are little winged critters that resemble tiny mosquitoes (don’t worry, they don’t sting!) and are similar in size to fruit flies. The good news is that these plant flies are much less harmful than many other pests, and better yet, they’re pretty easy to get rid of. 

What are Fungus Gnats?

If you see a small winged insect that looks like a fruit fly hovering around the soil of your houseplant, chances are it’s a fungus gnat. They have long legs (for a super tiny fly), transparent wings, and affinity for nutrient-rich, moist soils. Fungus gnats have very little interest in the leaves of your plants, instead, they focus on the moist soil below the plant canopy. They lay their eggs in the top layer of damp soil and eat the hair roots of your plants. While their damage can be minor, nothing is ruder than an uninvited guest laying eggs in your favourite plant and eating its roots! If left untreated, these bugs can eventually lead to wilting, poor growth, and discoloured leaves.

Signs of Fungus Gnats

fungus gnat larvae

If you have a gnat problem, you’ll know—they’re easy to spot! These flies aren’t actually great at flying, so they tend to stay pretty close to the plant. You’ll notice them whizzing about in zig-zag movements. If you gently stir around the soil, you might notice their tiny, transparent larvae. Using yellow sticky cards is a great way to monitor their activity AND is a good control option too. More on that below.

The Number One Way to Get Rid of Gnats

A fungus gnat infestation usually happens when there’s too much moisture in the soil. When plant parents give their plants the same care 12 months of the year, problems can occur. Think about it, our homes are usually brighter and more humid in the summer than during the winter. Most plants don’t grow as actively in the winter, they sense the seasonal change and go more dormant. By cutting back on watering, you can prevent fungus gnats from camping out in your plant pots.

Gnats lay their eggs in the top layer of soil, and for their eggs to survive, the soil needs to stay moist. Letting it dry out can kill the eggs and break the gnats’ life cycle! If your pot allows, soaking your houseplants from below is an ideal watering method. The soil surface stays dry while the soil soaks up water near the root ball. To do this, place the pot in a dish of water and let the water soak up through the drainage holes.

What If That Doesn’t Work?

 If you’ve changed up your watering schedule and the gnats are still hanging on, OR you want to kill those gnats FAST, you can step up your treatment plan. Here are a few easy ways to control gnats in your houseplants:

fungus gnat quote

Use sticky cards. You’ve likely seen the yellow cards on sticks in our greenhouse, but you may have wondered what they were for! Gnats love yellow and the cards are placed directly above the surface of the soil. Not only can you monitor what you have by checking what you’ve caught, but all the gnats that land on your card are eliminated! Be sure to replace your sticky card about every 4-6 weeks (or sooner if it’s covered in gnats).

Introduce beneficial nematodes. When we want to kill grubs in our lawn, we use beneficial nematodes. When we need to control fungus gnat eggs, we can add a different strain of nematodes to our watering can and unleash them on the gnats! Nematodes are microscopic bugs that attack gnats in their larval stage. Here at Heeman’s, we sell beneficial nematodes in a teabag-like sack you can add to your watering can. Easy! Fungus gnat nematodes are sold most of the year.

Hydrogen peroxide solution is a quick, cheap, and effective way to kill larvae on contact. Mix four parts water with one part hydrogen peroxide and spray down your soil. 

fungus gnat prevention houseplant watering soil

Fungus gnats are annoying, but they’re no match for a plant parent with a plan. Switch to less frequent watering during the winter and get in the habit of bottom-watering to avoid these icky pests—you will “gnat” be sorry!