How to Get Control of Fungus Gnats Outdoors

Mulch is a prime spot for fungus gnats to nest
Gnats tend to congregate in mulch and shrubbery.

While we frequently use the word “gnats” to refer to any number of tiny winged insects (such as biting midges and punkies), true fungus gnats are small non-biting insects that are drawn to wet, rotten organic matter where they lay their eggs and soon hatch into larvae.

In general, they are relatively harmless creatures, but their incessant swarming is annoying enough to drive even the toughest of gardeners indoors.

Like mosquitoes, fungus gnats can be difficult to control, because the problem may go beyond your property line.

It’s pretty hard to deal with any insect in your own yard if they’re flying in from a nearby lake or farm, and some parts of the world seem to be overrun during the warmer months.

Here are some tips to keep them away.


A little vanilla extract on the brim of your hat acts as a natural gnat repellent. (pixelshot)

How to Tend Your Yard to Avoid Fungus Gnats

Take these steps to make your yard less inviting to fungas gnats:

  • Keep your garden free of mold, fungus, and rotting plant debris. Pay particular attention to shady areas with poor air circulation. Put your compost pile as far from the house as you can, cover your trash cans, and keep fallen debris cleaned up.
  • Amend your garden soil to improve drainage.
  • Occasionally rake or turn your mulch to allow sodden, moldy layers to dry out.
  • Avoid overwatering, and allow enough time between waterings for the top layer of soil to dry out.
  • Water in the morning to avoid overnight fungal growth.
  • Make sure you have no standing water in gutters, drainage areas, or low spots.
  • Keep birdbaths and water features clean.
  • If your garden still has naturally damp areas, you can top dress the soil with an inch (or less) of sand, to discourage fungus gnats looking for moist soil.
  • Use sodium light bulbs in outdoor areas to reduce attraction at night.

Pinestraw
Mulch is great for holding in moisture, but it shouldn’t be moldy or soggy.

To address existing infestations, here are some other ideas:

  • BTi (Bacillus thuringiensis v israelensis), also known as Gnatrol, is a bacteria that effectively kills gnat larvae. It is most suitable if you can identify specific areas where gnat larvae are actively hatching and feeding.
  • Beneficial nematodes and predatory insects can provide long-term control of larvae once established in the garden.
  • Traps including liquid traps, sticky traps, and electronic insect devices can help control gnats in areas where the adult insects are swarming.

Gnat Trap
DIY your own gnat trap with pine oil, citronella and vanilla. (fotogal/Getty Images)

Repellents and Homemade Gnat Traps

  • Repellents: DEET, citronella, vanilla, pine oil, and dryer sheets are commonly used to repel gnats. You can also use fans on your porch to keep the air moving and discourage hovering swarms. There are also a number of repellent sprays, lanterns, and granules on the market that claim to repel gnats with varying degrees of effectiveness or toxicity.
  • Chemical controls: Foggers, sprays, and insecticides designed for flying insects will work with gnats, although they’re not particularly effective in preventing future infestations. Prevention is more effective, and less toxic, than chemical controls.

You can find a variety of organic fungus gnat control products, including repellents and predatory insects, at your local garden center or at online retailers such as Planet Natural and Golden Harvest Organics.

If you’re not sure what sort of insect you’re dealing with, or if you’re being bitten, contact your local agricultural extension service for advice specific to your region.

Further Reading