How To Prevent Gnats In Houseplants? Plus Effective Tips!

Gnats, particularly fungus gnats in houseplants, are unpleasant. They tend to lay eggs in moist potting soil. The moist soil feels like heaven to them for their egg-laying process and the organic matter in the ground to feed their larvae. As a result, this behavior of gnats damages the houseplants. Therefore, the indoor infestations of fungus gnats are most frustrating and challenging to control. In this article let’s talk about how to prevent gnats in houseplants.

Healthy and happy houseplants

What Are Fungus Gnats?

Fungus gnat on an outdoor leaf

Fungus gnats are small insects of the family Sciaridae. Due to high humidity and moisture, they are the most common pests of indoor plants. These tiny pests have long, narrow legs and segmented antennae larger than their heads.

Fungus gnats are easy to identify due to their large antennae and narrow legs.

The adult fungus gnats appear dark gray or black with transparent wings. Other than houseplants, they gathered around light sources or windows. The adult gnats are 1/16 to 1/8 inches long. While the fungus gnat larvae are 1/4 inch long with dark blackheads and shiny transparent or pale bodies.

A group of fungus gnat larvae (half the size of their adult)

The fungus gnat larvae reside in the soil and are predaceous eaters of plant roots. Their eating exposes the plant roots to secondary pests such as root rot pathogens. The damage to their feeding appears so late that it becomes impossible to revive the health of the houseplant.

Important Tip: The first place to look for fungus gnat infestation is the base of potted plants because the female fungus gnats lay eggs in moist, damp soil rich in organic matter.

Note: Although they resemble fruit flies, they lay eggs in the damp soil of potted plants while the fruit flies lay their eggs on rotten fruits and vegetables.

Identifying the Damage of Fungus Gnats on Houseplants

The good news is that the adult gnats do not cause much harm to indoor plants. However, their presence is frustrating and noisy. On the other hand, the larvae of fungus gnats tend to cause severe damage. This is because the larvae feed on young plant roots and seedlings. Thus, the feeding impacts the plant’s ability to absorb nutrients from the soil and exposes them to secondary pathogens.

Damage caused by the feeding of fungus gnats

The root damage by larvae leads to sudden wilting of affected plants, loss of vigor, and yellowing and falling of plant leaves. The severe infestations cause extensive losses of plants.

Severely damaged by plant larvae, the young seedlings turn brown with distorted bark.

Host Plants of Fungus Gnats

The following plants are prone to fungus gnat infestations:

Poinsettia root damage due to the feeding of gnat larvae (it exposes the roots to fungal pathogens)

1. Poinsettia
2. Geraniums
3. African violets
4. Carnations

Life Cycle of Fungus Gnats

Adult fungus gnats on one side and the larvae of gnats on right 

The warm, humid weather of indoor environments attracts most insect pests— because interior spaces provide the ideal conditions for their growth and reproduction. Similarly, the fungus gnats prefer indoor spaces to grow and thrive.

The female fungus gnats live almost one week and lay up to 300 eggs in moist and nutrient-rich soil. The newly hatched larvae (within 4 to 6 days of hatching) feed on young roots and decaying plant material for their two-week period. Then, they undergo the pupation stage.

During the pupal stage, they remain sessile and do not eat. This stage lasts for 3 to 4 days before the adults emerge from the ground and are ready to start the next generation cycle.

The entire lifecycle from eggs to adults completes within three to four weeks depending upon temperature and damp soil surface. Therefore, potted plants can have overlapping generations per plant under the right conditions, including eggs, larvae, pupae, and adults. In addition to that, the fungus gnats also have a short generation cycle.

The complete life cycle of fungus gnats from eggs to adults

Important Tip: After careful monitoring, repeat spray of neem oil, insecticidal soap, and vegetable oil to completely kill the eggs and larvae on the potting soil surface.

How to Prevent Gnats in Houseplants?

Fungus gnat problems get indoors mainly due to the following reasons:

1. You buy a plant already contaminated with fungus gnats
2. You may receive contaminated plants as a gift
3. You get fungus gnat infestations due to shifting plants from outdoors (the adults lay eggs in soil) to indoors

Cultural Practices

To prevent fungus gnats infestations, follow the below-mentioned tips:

1. Quarantine the newly purchased plants outdoors for at least two weeks (according to their life cycle) to check for fungus gnats infestation
2. Isolate the plants within a room for 17 to 18 days to inspect for adult gnats infestation. Once the plant is clear, it does not show any damage and infestation; move the plants with other indoor plants.
3. Do not overwater the houseplants because of the female gnats’ excess moisture for egg-laying.
4. Keep the soil dry by watering. To check soil moisture levels, press the palm of your hand against potting soil, and if you do not feel any moisture, then the potting soil is okay for watering.
5. Do not overfeed the plant with nutrients because the excessive nutrient applications will encourage new growths and fungus gnat larvae are fond of tender developments.
6. If you notice any infestation of adult gnats, let the soil dry to the depth of one inch around the base of the houseplant. This approach is wiser because dry soil will repel the harmful pests and discourage their egg-laying sites (soil moist). 
7. Keep the indoor spaces around houseplants clean to avoid the fungus gnat problem. Remove dead, dried, and fallen leaves because these may provide the adults a hiding place or egg-laying site.
8. Use sterile potting mix. This benefit is that it will not have any fungus gnats eggs, larvae, and pupae. Avoid mixing organic materials such as peat moss because it will provide the female’s sites for egg-laying.

Create a DIY Gnat Trap Using Vinegar

1. Take one tablespoon of sugar in a bowl.
2. Take 2 to 3 drops of liquid dish soap and one tablespoon of white vinegar in a bowl. Mix all the ingredients in a bowl and cover it with a foil or plastic paper.
3. Poke several small holes in the foil and place the bowl near houseplants to capture flying fungus gnats
4. This DIY remedy has similar benefits as the yellow sticky traps.

White vinegar near houseplants

How to Get Rid of Gnats on Indoor Plants?

The adult gnats do not cause much harm to plants, but if their occurrence goes uncontrolled, they can be an absolute disaster. They will annoy you and fly around your home spaces and lay eggs in the base of the houseplants. So, to get rid of gnats, employ the following practices:

Use Yellow Sticky Fly Traps

Yellow sticky fly traps for the trapping of adult fungus gnats

Flying sticky trap with captured fungus gnats

The best way to reduce the population of adult fungus gnats in indoor spaces is to use sticky traps. These traps will capture the adults, thus reducing the chances of further new generations of houseplants.

The yellow sticky fly traps comprise yellow paper with a sticky material. These sticky traps are also present in orchards or more extensive garden sections to trap various pests. Unfortunately, the fungus gnats are attracted to the bright yellow color and get stuck on it.

Sticky traps are a non-toxic way of eliminating the adult fungus gnats. It is also the best option to monitor the pests in indoor environments to determine whether the pest population has become a problem.

Use Potato Slices to Trap and Kill Fungus Gnat Larvae

Raw potato slices to determine the intensity of larvae of fungus gnats

Gnat larvae love raw potato slices. Therefore, these potato chunks can be used as a trap against them. Place two or three raw potato chunks near your houseplant’s base or soil surface and look for three to four hours.

If the potato slice is overcrowded with gnats larvae, re-pot the plant in a new pot with a unique and sterilized potting mix. Also, change the soil around the plant roots to destroy the eggs of gnats.

Spray Fungus Gnats With Liquid Dish Soap

1. Mix one tablespoon of mild liquid dish soap and apple cider vinegar in a bowl.
2. Take one teaspoon of baking soda per cup of water.
3. Mix all the ingredients and pour them into a spray bottle.
4. Spray the mixture on the plants to repel the gnats that lay eggs in the soil of potted plants

Liquid dish soap spray to repel gnats on houseplants

Use Hydrogen Peroxide Mix to Get Rid of Gnats

Hydrogen peroxide spray to kill gnats larvae and their eggs

1. Take 1/2 cup of 3% hydrogen peroxide.
2. Take two cups of water in a bowl and mix it with hydrogen peroxide.
3. Apply this mixture onto the foliage and soil to repel adults and kill larvae and eggs.
4. This hydrogen peroxide dilution can be used as a drench before putting the soil in the pot.

Note: Like neem oil spray, hydrogen peroxide effectively controls fungal pathogens, mites, and insect pests.

Apply Beneficial Insects

There are numerous enemies of fungus gnats, such as predatory mite (Hypoaspis miles), many nematode species, and rove beetle. These natural enemies feed on all stages of gnats and help get rid of fungus gnats.

Hypoaspis miles eat the first stage larvae of gnats and can help early control pests. 

Hypoaspis miles play an essential role in the larvae control of gnats, aphids, thrips, and springtails. It predates the pests and prevents plants from their infestations. However, the early release of this mite in the growing season contains the invasive pest and maintains the cosmetic value of plants.

FAQs

What Is the Best Trap for Gnats?

A white vinegar trap is the best one for gnats. It determines the population intensity of adult gnats and helps develop the strategy to control the gnat problem on houseplants.

What Causes Fungus Gnats?

The warm, dry, and humid conditions of indoor spaces attract the gnats in homes. However, once the gnats are inside the house, they remain close to their food sources: organic matter and fungus in the soil. 

The adult females lay their eggs in the soil, and the newly hatched larvae feed on the organic matter present in the ground and the roots of young seedlings. Most of the time, their infestation goes unnoticed until a houseplant owner observes their feeding trails, similar to slugs and snails.

The larvae cause much damage to plants, and they remain in this stage for ten days. Then, they undergo the pupal stage.

 The life cycle of gnats is completed in three weeks, with more than 6 to 8 generations per growing season. So to get rid of gnats, early detection and management are critical.

How Do You Make Homemade Bug Spray for Plants?

1. Mix one tablespoon of baking soda with one tablespoon of sugar and three drops of mild dish soap in a bowl
2. Add four cups of water to it and mix it well.
3. Pour the solution into a spray bottle and use it as a repellent and larvae killer.

What Is a Good Gnat Repellent?

The apple cider vinegar and baking soda are good gnat repellent. It also prevents foliage damage by other houseplant pests. To keep the problems away, reapply them every three to four days and ensure it is uniformly distributed on plant foliage.

Sources for Further Reading

1. Planet Natural. (2019a, November 11). How to Get Rid of Fungus Gnats. Retrieved April 3, 2022, from https://www.planetnatural.com/pest-problem-solver/houseplant-pests/fungus-gnat-control/
2. Dampier, J. (2021, September 2). Fungus Gnats on Houseplants. Wisconsin Horticulture. Retrieved April 3, 2022, from https://hort.extension.wisc.edu/articles/fungus-gnats-on-houseplants/
3. Fungus Gnats | New York State Integrated Pest Management. (n.d.). Cornell University. Retrieved April 3, 2022, from https://nysipm.cornell.edu/whats-bugging-you/flies-non-biting/fungus-gnats/

Now that you know how to prevent gnats in houseplants, read our other articles about plant pests:

Aphids on Indoor Houseplants: 10+ Smart Ways to Get Rid of Them!

Root Maggots: How to Get Rid of Root Eating Insect Pest Naturally?

How to Get Rid of Wireworms Effectively?