If you're annoyed by tiny flying insects that appear every time you water your houseplants, you're probably dealing with gnats—more 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. Besides being annoying, this feeding behavior can damage your plants.
Often indoor plants get gnats when plants are being overwatered. To get rid of the infestation, a good place to start is to let the soil dry out between waterings to discourage gnats from making your plants their home.
If you want to get rid of gnats in your indoor potted plants, you can use common 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 tiny mosquitoes, fungus gnats are small flies of the Orfelia and Bradysia species. They are fairly 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. If you notice these gnats flitting about and your plants seem to wilt for no reason, larval root damage could be the cause.
Fungus gnats do not bite people or pets. The adult gnats don't do much damage to plants; instead, the larvae will munch on your plant's tiny feeder roots, limiting the plant's ability to take up nutrients and stunting its growth. Fungus gnats are primarily a problem in nurseries, where many susceptible young seedlings are grown in damp conditions. While you may not be growing your plants in a nursery or greenhouse setting with a large enough population, they can also pose a threat to common houseplants.
Natural Ways to Get Rid of Fungus Gnats
If you find a fungus gnat problem, try to quarantine the infected pots away from other houseplants so the problem does not get worse or spread. Since both the majority of the life of fungus gnats and the damage they do take place when they are in the soil, this is an excellent place to begin targeting them.
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 not as much organic matter for the young to feed on.
Hydrogen Peroxide As Larvacide
Mix one part of hydrogen peroxide and four parts of water. Use this solution to water your plants. Hydrogen peroxide will kill the gnat larvae and not injure your plant. Keep reapplying weekly until you notice the gnats are gone.
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. They'll be attracted by the scent, try to sip the solution, and drown.
Soap Acts as an Insecticide
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, killing bugs by suffocation and dehydration. The soaps break down the insect's protective body surface.
Cinnamon and Chamomile Kill Fungal Food Sources
Both ground cinnamon and chamomile tea are natural fungicides. Since fungus gnats snack on fungus, killing their food source sends them away.
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.
The adults 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 traps. These are exactly what they sound like: sheets of yellow paper with adhesive. Yellow sticky traps are sold in the pesticide section of your garden center. You can also find small versions that come with little stakes that you stab into the soil.
Fungus gnats are attracted to the color 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.
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 for watering 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?
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.
Since the larvae do the bulk of the damage, it helps to be aware of the fungus gnat's life cycle. The tiny eggs can hatch into larvae in a warm house in only three days. They remain in the larval stage for another 10 days before developing into pupae. Approximately four days later, the adults emerge and start the cycle again. They can produce a new generation of fungus gnats in less than three weeks, so catch them early to make it easier to eliminate them.
Preventing Fungus Gnats in Houseplants
Fungus gnats commonly get into a house either because the plants have been outdoors, where adult gnats can lay their eggs into the soil, or the plants came from their source with contaminated soil. The only way to prevent this migration is to avoid bringing the plants inside. Of course, houseplants, by definition, live indoors, so this is not a permanent solution.
The best answer is to quarantine new plants or those that have been outdoors for extended periods. Keep the plants in their own room for at least 17 days (a full life cycle), and inspect the plant carefully 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, be careful not to overwater your houseplants since soggy soil and a full runoff saucer are just what the gnats are looking for. 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.
Do worms eat fungus gnats?
Steinernema feltiae is a nematode that feeds on fungus gnat larvae and release a bacterium that kills them. The nematodes typically must be mail-ordered from a plant pest control company, so this solution can be more of a hassle than other, quicker remedies.
Can I spray fungus gnats?
Biological and synthetic insecticide sprays are effective for quick results against fungus gnats, but they are not a long-term solution and are seldom necessary. Common options include pyrethrins, permethrin, and bifenthrin. Sprays can harm beneficial insects, so use them carefully and judiciously. Typical application involves spraying the soil surface and the plant parts where adult gnats tend to land.
Do fungus gnats fly around the house?
Fungus gnats are relatively slow flyers that typically hang out on the soil of plants or nearby the plants, although they may venture out far enough to fly near your face if you're sitting close to a plant. Again, they are harmless to humans, and they do not bite. Think of them as fruit flies that hang around plants instead of fruit.
“Fungus Gnats as Houseplant and Indoor Pests - 5.584.” Colorado State Extension,