How to Get Rid of Fungus Gnats in Houseplants Naturally

If you notice tiny flying insects that appear every time you water your houseplants, you're probably dealing with gnats—specifically fungus gnats. These pests are attracted to the damp soil of potted houseplants. They need moist soil to lay their eggs, and the organic matter in the dirt feeds their larvae.

Fungus gnats do not bite people or pets. Adult gnats don't do much damage to plants; instead, larvae munch on your plant's tiny feeder roots, limiting the plant's ability to take up nutrients and stunting its growth. Larval root damage commonly causes wilting, among other problems.

Often, overwatered indoor plants attract gnats. Let the soil dry out between waterings to discourage gnats from making your plants their home. Try easy home remedies like hydrogen peroxide, vinegar, and cinnamon—without killing your plants. Read on to find more ways to get rid of gnats in plants naturally.

What Are Fungus Gnats?

Although they look like mini mosquitoes, fungus gnats are small flies of the Orfelia and Bradysia species. They are tiny insects. They can be identified by their narrow legs, light gray or clear wings, and segmented antennae larger than their heads. The adults grow to be about 1/16 to 1/8 inch long.

Fungus gnats tend to remain near their source of food—the organic matter and fungus in the soil. The adults lay their eggs in the soil, and the emerging larvae feed on the soil's organic material and the plant's root hairs.

The larvae are 1/4 inch-long, translucent white or gray worms with shiny black heads. They may go unnoticed at this stage unless you have a crop of them; then, you could see slime trails similar to those of snails and slugs.

A fungus gnat's life cycle is fast. Tiny eggs in a warm house hatch in three days after being laid. They remain as larvae for 10 days before pupating. The pupa stage is four days, emerging as flying adults that immediately start the cycle again. The flying gnats naturally end their life cycle in two to three weeks and can lay up to 200 eggs.

Signs of Fungus Gnats in Houseplants

Any plant can develop a fungus gnat infestation, but certain plants are more predisposed, such as African violets, geraniums, carnations, cyclamens, and poinsettias.

Plants show these signs when there's a fungus gnat presence:

• Appearance of tiny flying insects that emerge after watering
• Noticing 1/4-inch-long worms or their slime trails in the soil
• Sudden, unexplained wilting
  
• Appears limp or no longer vigorous
• Stops growing or growth is stunted
• Leaves start yellowing

Natural Ways to Get Rid of Fungus Gnats

If you find a fungus gnat problem, quarantine the infected pots away from other houseplants so the problem does not get worse or spread. Since the fungus gnats' life cycle and main damage primarily occur in the soil, start with the soil.

Let the Soil Dry

The easiest first step is to allow the soil to remain dry for several days before watering again. Both the eggs and the larvae will eventually die off in dry soil. Also, remove any standing water from runoff saucers. Another easy tip is to use a sterile potting mix because there is less organic matter for the young to feed on.

Use Hydrogen Peroxide as Larvacide

Mix one part hydrogen peroxide and four parts water. Use this solution to water your plants. Hydrogen peroxide will kill the gnat larvae without injuring your plant. Keep reapplying weekly until you notice the gnats are gone.

Try Vinegar for a Gnat Trap

Pour apple cider vinegar into a cup or glass and mix in a few drops of dish soap. Cover it with tape or cheesecloth, leaving holes large enough for the bugs to get to it. The scent will attract the bugs and they sip the solution and drown.

Suffocate Bugs With Soap

You can use dish soap or Castile soap to kill any soft-body insects. Both are considered effective insecticidal soaps, particularly Castile, which has plant-based oils. The soap kills bugs by suffocating and dehydrating them, breaking down the insect's protective body surface.

Kill Fungal Food Sources With Cinnamon and Chamomile

Both ground cinnamon and chamomile tea are natural fungicides. Since fungus gnats snack on fungus, killing their food source sends them away.

Trap Them With Potatoes

Existing fungus gnat larvae can be trapped using pieces of raw potato. Place the potato pieces flesh side down on the soil and check under them every couple of days. Remove any feeding larvae, and replace the potato with fresh pieces. Do not let the potatoes dry out.

Catch Them With Sticky Traps

Adult gnats have short lives, but reducing their population will also reduce the number of new eggs being laid. To control adult fungus gnats, use yellow sticky fly traps. These traps are precisely what they sound like—sheets of paper with adhesive.

Fungus gnats are attracted to yellow and get stuck in the traps. When the trap is full, throw it away and place another one. It's not a pretty sight, but it is an easy, nontoxic way to eliminate large quantities of adult fungus gnats. It is also a great way to monitor fungus gnats' presence and see if their population has become a problem.

Yellow sticky traps are sold in the pesticide section of your garden center. You can also find small versions with little stakes to stab into the soil.

Apply Biological Controls

There are a handful of biological controls for fungus gnats, but they are mainly used in greenhouses where plants are being propagated. If a gnat problem gets so out of hand with houseplants that you are considering biological controls, you are probably better off sacrificing your houseplants and starting over.

However, if you want to try botanical controls, the best choice is Bacillus thuringiensis subspecies israelensis (Bti), the same bacteria used for mosquito control in ponds. These bacteria control gnats but pose no risk to people or pets. Look for "Bt" in the form of mosquito dunks or granules (in the pest control section or near pond supplies in a home or garden center).

Mosquito dunks are dissolved in water, and the solution is used to water the plants. You will probably need more than one application, but follow the label instructions. Granules are sprinkled over the soil, introducing some bacteria with each watering.

What Causes Fungus Gnats?

Contaminated soil is the main culprit. A fungus gnat problem often starts in nurseries, where many susceptible young seedlings are grown in damp conditions. You may be bringing home a problem without even knowing it.

Plants brought inside from your outdoor space with hidden fungus gnat larvae in the soil are often the other cause.

Preventing Fungus Gnats in Houseplants

The only surefire way to prevent fungus gnats from migrating into the home is to avoid bringing plants inside. Before bringing a houseplant indoors, quarantine new plants or those living outdoors for extended periods.

Keep the plants apart for at least 17 days (to account for the gnat's life cycle), scrutinizing them for the presence of adult gnats. Once the plant has been cleared with no insect activity, you can move it in with your other plants.

As an ongoing prevention method, avoid overwatering your houseplants. Soggy soil and a full runoff saucer attract gnats. Let the soil dry between waterings, but only as much as the plant will tolerate; this is no reason to threaten your plant's vitality.