How to Get Rid of Gnats in Plants and Houseplants

  • Written By Dan Edwards on February 2, 2021
    Last Updated: February 2, 2021

Gnats can make your once beautiful houseplants look unsightly, be an incredible nuisance in the home, and possibly terminally harm your flora-babies.

With a little attention and care, you can eliminate the problem, often without the use of harsh chemicals. Allow us to reveal the secrets of removing these unwanted pests.


You can get rid of gnats in plants and houseplants with these methods:

  • Don’t overwater
  • Sprinkle the soil with cinnamon
  • Ensnare gnats with yellow sticky traps
  • Check your soil
  • Surround the plant with sand

What Gnats Affect Houseplants and Plants?

Often, people refer to the tiny gnats around their plants as fruit flies; however, this is usually incorrect. Fruit flies, known scientifically as drosophila, are only interested in three things — fruit, vinegar, and wine. Hence, if they’re loitering around your bowl of oranges, they’re fruit flies. They have little to no interest in plants or houseplants. This isn’t their food source, and so they steer clear.

Fungus gnats, however, love indoor and outdoor plants. They lay their eggs in the earth, which then hatch into larvae — and that’s bad news.

These maggot-like wrigglers eat the small fungi growths in moist soil, but they don’t stop there. They can munch through the thin roots of young plants and attack the stem, which may cause bacterial infection.

Do I Have Fungus Gnats?

Knowing the symptoms of a gnat infestation in your plants means you can act quickly, addressing the issue before it becomes an epidemic.

Signs to look out for include:

  • Small gnats flying around, or sitting on, your plant
  • Slender, white larvae in the topsoil
  • A plant that’s yellowing or wilts suddenly
  • Damage to the stem where it meets the topsoil

The larvae can sometimes be hard to spot, especially if they’ve only just hatched. However, you can draw them out with some advice from the University of Ohio.

  1. Place chunks of potato — without peel — around the base of your plant
  2. The larvae are attracted by the moisture and starch in the vegetable and will begin to assemble underneath
  3. Leave for 48 hours
  4. Turn the potato pieces over and check for signs of infestation

How to Get Rid of Fungus Gnats in Plants

Solving your fungus gnat issue means a two-pronged approach — treatment and prevention.

There’s little point eliminating these annoying pests only to allow them to return. Here are our top tips in keeping your plants gnat-free.

Treatment

Eliminating adult gnats and destroying their larvae are the best ways to treat gnats in plants and houseplants.

Eliminate the Adults

We always recommend first eradicating the adult flying fungus gnats. This means that there are no creatures to lay any further eggs.

You can purchase chemical-based sprays that contain the pesticide cyfluthrin. We’d consider this a little extreme, as the adult gnats aren’t that resilient to require such drastic treatment — and this compound is toxic to humans and animals.

Instead, consider one of the many ecologically friendly sprays which contain essential oils — proven to deter these tiny critters.

One of our favorite treatments, due to being harmless — well, not to gnats— are yellow sticky traps. You place them horizontally around the base of plants — the gnats land on them and become stuck. Scientists explain that fungus gnats adore the color yellow and are unable to resist these environmentally friendly treatments.

Destroy the Larvae

With the flying gnats taken care of, it’s time to address the larvae before they pupate and become adults.

A rather pleasant-smelling method is to reach into your spice cupboard and pull out the cinnamon. Sprinkle on the surface of the soil around your plants and wait. The larvae will eat this spice and then die. 

While it may sound like an old wives’ tale, studies show that both powdered cinnamon and oil are effective methods to control both gnat and mosquito problems. 

If the infestation is severe, you may have to revert to slightly more powerful treatments:

  • Bacillus thuringiensis — a selective pesticide that kills fungus gnat larvae, yet will not damage you, your houseplants or your pets
  • Azadirachtin — destroys wriggling gnats when they come into contact with the compound
  • Nematodes — microscopic worms that eat the larvae from the inside out, but won’t harm your flora

Listen up.

Eradicating the adult flying insects is a relatively quick procedure. Destroying the larvae will take longer.

Both the natural and synthetic compounds require a few days for the effects to become noticeable. Furthermore, while you may be destroying the already existent larvae, a new batch may be emerging from eggs in the soil.

Continue to address the larvae issue for around 21 days, reapplying treatments every five to six days. This should ensure you destroy all generations.

Prevention

Go Steady on the Water

Extremely wet topsoil is like a neon advertising hoarding to a fungus gnat. Allow the top inch of your houseplants’ potting earth to dry out entirely before rewatering — taking away the gnats’ temptation.

Research from the University of Vermont explains that this is sensible plant housekeeping advice in general, promoting a healthy plant that won’t rot.

Alternatively, if you’re not bothered by its gritty and yellow appearance, make a half-inch layer of sand around the base of your plants. This will both enable the water to quickly drain beneath and prevent the gnats from laying eggs in the soil.

Be Selective With Potting Compost

Only purchase good quality potting earth from reliable sources. It’s possible that lower-quality compost may already contain eggs or larvae from the fungus gnat. When you’ve bought a new supply, first tip it out onto a newspaper or other medium and look through the soil for signs of infestation.

Check Your Plants

You see a beautiful, glossy and healthy-looking plant in your local garden center, and you know it will look amazing in your living room. Before you whip out your credit card, check it for signs of fungus gnats. Just because no flying insects are circling the plant, it doesn’t mean the eggs and larvae aren’t there.

Gently turn over the top half-inch of soil and look for the white/transparent black-headed larvae. If you see any evidence, don’t buy. Once in your home, this plant could begin to infect your other established favorites.

Conclusion

Gnats on your houseplants and plants are unsightly and may lead to a pathetic and sick looking flower or shrub. By following the measures we’ve outlined above, these tiny terrors can be easily eradicated.

Always act fast — it only takes one flying adult to glide from one plant to another, and the problem will exacerbate. Check those prized begonias, now!