How to Get Rid of Gnats on Houseplants and Kill Gnats in Plant Soil

By Jessica Nolan, Gardening Expert Houseplants

Fungus gnats, also called soil gnats, are small flying bugs that are the bugbear of anyone who has houseplants. The tiny flying pests lay their eggs in the potting soil where they hatch into larvae. The gnat larvae thrive in damp soil and can quickly harm the roots of young plants. You may notice these bugs in your houseplant soil or they may fly around your plants. When gnat larvae grow into flying insects, the gnats can quickly infest other plants in your home with fungal diseases.

How to get rid of gnats in houseplants: The best way to get rid of fungus gnats is to disrupt their lifecycle. Neem oil, hydrogen peroxide soil drenches, beneficial nematodes, and pyrethrins are all excellent for killing gnats, their eggs and larvae in plant pot soil. You can also use yellow sticky traps to catch and kill flying gnats.

Fungus gnats are from the superfamily Sciaroidea, and their larvae feed on the fungus growing in soil. Apart from fungus gnats infesting your plants, they are also annoying pests in your home. So, getting rid of gnats on houseplants helps keep your plants healthy and stops the infuriating flies from irritating you.

How to Eliminate Fungus Gnats on Houseplants and In the Soil

As soon as you spot tiny gnats flying around your plants, you need to act quickly. While some pesticides can quickly kill off gnats, you probably don’t want potentially dangerous chemicals in your home.

So, what are some of the natural solutions for eradicating gnats from houseplants?

Here is a list of helpful natural ways to get rid of fungus gnats and kill these bugs in houseplant soil:

Hydrogen peroxide to kill off fungus gnat larvae —Make a soil drench with hydrogen peroxide 3% to flush the soil and kill these bugs in the plant soil. This remedy helps kill off gnat larvae in the soil to break their lifecycle.

Neem oil to eliminate houseplant flies —This oil is a natural insecticide that disrupts the fungus gnats’ hormones. You can use neem oil as both a soil flush and an organic insecticidal homemade spray.

Yellow sticky traps to kill flying gnats—Gnats are attracted to yellow color and will die when they stick to the traps. These gnat solutions help reduce gnat numbers and break the breeding cycle.

Beneficial nematodes to kill fungus gnat larvae—Some types of microscopic roundworms (Nematoda) are useful because they feed on fungus gnat larvae. The benefits are that they don’t affect your plant but kill off tiny bugs in the houseplant soil.

Apple cider vinegar (ACV) fungus gnats trap—Mixing ACV with some sugar and dish soap attracts tiny flying pests and traps them.

Diatomaceous earth (DE) to kill plant flies—Another way to get rid of flying gnats is to put a layer of DE on your plant pot soil. Diatomaceous earth is a naturally occurring silica powder that should kill these bugs as they emerge from the potting soil.

Fungus Gnat Overview

Fungus gnats are common houseplant pests in the family Sciaridae. These tiny flying insects measure between 0.08” and 0.3” (2 – 8 mm) long. Gnat larvae feed on fungus in potting soil where they can affect the health of young plants or weak plants. Fungus gnats can carry fungal diseases to other plants. So, getting rid of these bugs from houseplants is a top priority.

Fungus Gnat or Fruit Flies?

Mexican fruit fly (Anastrepha ludens)

Identifying the difference between fruit flies and fungus gnats is essential if you want to get rid of them. Gnats are dark gray to black and look like tiny mosquitoes. In comparison, fruit flies have a rounded body and look more like the common housefly. You will also notice that fungus gnats only tend to be around plants—flying around them or crawling over the soil or leaves. Fruit flies usually hover around rotten fruit or near garbage cans.

What Are the Symptoms of Fungus Gnats on Plants?

How do you know that fungus gnats are affecting your houseplants? If your plants at home are generally healthy and there are only a few flies, it can be challenging to spot sight of houseplant gnats. Of course, seeing minuscule mosquito-like flies is a sign of a gnat problem.

If your potting mix is infected with gnat eggs and larvae, you may start to see evidence of their activity on your plant. Some common symptoms of gnats on houseplants include:

Weak plant growth
Leaves that begin to turn yellow
Plants that start to die

Life Cycle of Fungus Gnats

To successfully get rid of fungus gnats for good, you need to know something about their lifecycle. The gnats have a quick lifecycle and multiply prolifically. The breeding and reproduction patterns are reasons to eliminate gnats as soon as possible

Fungus Gnat Eggs

One adult gnat can lay up to three hundred eggs in its one-week lifespan. The females lay eggs at the base of plants. After about four to six days, larvae emerge, and the little grubs start feeding on organic matter.

Fungus Gnat Larvae

Gnat larvae live in soil, and these bugs munch their way through decaying plant matter. They quickly become larger and will grow to about 0.25” (6 mm) in two weeks. If there is little organic matter in the soil or plant roots have a fungal disease, the tiny white bugs will start eating their way through your plant. Once they reach full size, they enter the pupal stage. The first three stages—egg, larva, and pupa—all take place in houseplant soil.

Fungus Gnat Flies

After the pupal stage that lasts for three to four days, the tiny adult gnats emerge from the soil. Then the cycle starts all over again.

The key to getting rid of gnats for good is eliminating each stage of their life cycle. You not only need to kill the tiny flying pests—you need to eradicate the larvae and the eggs.

How To Get Rid Of Fungus Gnats

How can you combat a fungus gnat infestation? Let’s look at some of the best gnat control methods you can use. You probably need to use a combination of ways if you want to say goodbye to these bugs for good.

Water Houseplants Sparingly to Prevent Gnat Bugs in Soil

The first step to eliminating fungus gnats is to make sure and water houseplants properly. Gnat eggs and larvae need moist, damp soil to thrive. So, allow the top 2” (5 cm) of soil to dry out before watering your houseplant. This means you should avoid watering on a set schedule. Always check that the plant soil is partly dry before adding water.

Soggy soil only creates an environment where fungus gnats thrive. There are two reasons for this:

Fungus gnats and larvae need moisture to survive. Without moisture, they die off.
Egg-laying female gnats are attracted to damp soil to lay eggs. So, dry plant pot soil is not attractive to these pesky gnats.

Remember that in winter, you need to water less frequently than during summer.

Yellow Sticky Stakes to Trap Gnat Flies

Sticky yellow strips are essential to winning your battle against these tiny flying bugs. These traps help to capture a large number of adult gnats and prevent them from laying more eggs. Place the yellow fungus gnat traps horizontally at the soil surface. The more traps you use, the more flies you will catch.

Of course, yellow sticky traps only kill adult gnats. In addition to the traps, you need to address the issue of gnat eggs and larvae growing in your houseplant soil.

Hydrogen Peroxide to Kill Fungus Gnat Bugs in Houseplant Soil

Hydrogen peroxide 3% is an easy way to kill soil gnats when they’re in the egg, larval, or pupal stage. Hydrogen peroxide destroys gnat larvae and eggs on contact. Getting rid of the gnat eggs and larvae stops more bugs growing in the soil and helps break the life cycle.

To get rid of gnats in houseplants, you can make a hydrogen peroxide soil drench.

This is what you should do to kill bugs in potting soil:

Allow the top two inches (5 cm) of potting soil in your houseplant to dry out.
Mix one-part hydrogen peroxide (3%) with four parts of water.
Thoroughly water plants with the hydrogen peroxide solution to kill bugs in soil and allow all the liquid to drain.

The antifungal and sterilizing effect of hydrogen peroxide helps to sterilize potting soil and kill off gnat larvae in the soil.

Other Ways to Sterilize the Potting Soil and Get Rid of Bugs in Houseplant Soil

There are different methods—albeit time-consuming methods—of sterilizing potting soil. For these methods to work, you should remove the plant from the container, rinse all soil from the roots, and submerge the entire plant in soapy water. After sterilizing the soil, rinse your plant and repot.

Once you have prepped your plant, you can sterilize potting soil.

Here are a few methods to kill bugs in plant soil:

Microwave method—Put moistened potting mix in a microwave and heat for 90 seconds to get rid of bugs in plant soil. The temperature needs to reach between 160°F and 180°F (71°C – 82°) to kill off any soil bugs.
Sun method—You can remove the potting soil and place it outdoors in the hot sun for four to six weeks to get rid of tiny bugs in plant soil.

Most houseplant owners don’t bother with these time-consuming methods. In many cases, it is best to discard the infested soil and replace it with a new, fresh sterile potting mix.

Neem oil for Fungus Gnat Larvae Control

Neem oil has many uses when it comes to natural, organic pest control. A neem oil spray is useful for getting rid of many types of houseplant pests and bugs—including gnats—from leaves. You can also create a neem oil soil drench. Neem oil is highly toxic to gnats and fruit flies but won’t harm you or your plants.

According to scientific research, neem oil is an effective, safe alternative to pesticides. The oil disrupts the development of eggs, larvae, and pupae. Also, neem oil acts as a deterrent and helps prevent female gnats from laying eggs in the soil. In the end, neem oil poisons many houseplant pests to kill them off naturally. (1)

Neem oil soil drench to kill off gnats

You can create an organic, natural neem oil soil drench to eradicate soil bugs. Before drenching your soil with the bug-destroying liquid, wait until the top part of the soil is dry.

This is what you should do to destroy the fungus gnat life cycle:

Mix four teaspoons of neem oil and one teaspoon of liquid soap with one gallon (3.7 l) of water.
Thoroughly mix the oil and water.
Water your plants with the neem oil and allow it to drain.
Continue using the neem oil drench until you no longer have signs of gnats.

Neem oil natural insecticidal spray for gnats

To make a homemade gnat spray with neem oil, this is what you should do:

Put one tablespoon neem oil and one teaspoon of liquid dish soap in one-quart (1-liter) spray bottle.
Fill with water and shake well.
Spray your plant leaves and stems once a week and leave to dry.
The residual effect of neem oil should eventually kill flying gnats.

Food Grade Diatomaceous Earth (DE) To Kill Gnats

Diatomaceous earth is mineralized fossil dust that acts as a non-toxic pesticide. You can sprinkle a layer of DE on potting soil to kill plant flies as they emerge from the soil. The microscopic silica cuts through the outer skin of gnats when they come into contact with it. The good news is that DE won’t affect your houseplants, pets, or humans.

How to use diatomaceous earth to kill gnats:

As a precaution, put on a mask to avoid breathing in the dust.
Sprinkle the powdered DE on top of a dry potting soil in your planter and leave for two weeks.
Re apply DE after watering the plant until the little black flying bugs are gone.

When using DE, the soil must always be dry. So, allow the top part of the soil to dry out before applying.

Pyrethrin Sprays to Get Rid Off the Small Flying Bugs

You can eliminate gnats, their eggs and larvae by using pyrethrin sprays. Pyrethrins are natural organic compounds with insecticidal activity. You can purchase the sprays online or at garden centers. All you have to do is lightly mist the leaves to repel flying gnats. If you’ve got soil bugs, then spray the soil so that the top two inches (5 cm) of soil are moist.

Apple Cider Vinegar (ACV) For Getting Rid of Fungus Gnats

You could try using a vinegar trap to kill off flying gnats. Although using vinegar won’t eliminate all fungus gnats, it can help bring down their numbers. But you need to use vinegar traps alongside other natural fungus gnat control methods.

How to make an apple cider vinegar trap for gnats:

Mix 2 tbsp. ACV, 1 tbsp. sugar, and 1 tsp. liquid dish soap with 5 fl. oz. (150 ml) warm water.
Mix thoroughly until all the ingredients are dissolved.
Put the ACV solution in small containers, near where gnats are flying.
The sugar and vinegar should attract the gnats to the trap, and the dish soap will prevent them from flying away.

Cinnamon Trap for Fungus Gnats

Some people claim you can use cinnamon powder to kill off gnats and gnat larvae. The idea is that cinnamon has antifungal properties and destroys pathogens in the soil that larvae feed on. Over time, the tiny grubs should die off, and you’ll no longer have any flies.

There is no scientific evidence that cinnamon fungus gnat traps work. But if you want to try it, sprinkle a layer of cinnamon over the soil of an infested pot plant. Even if the cinnamon gnat trap doesn’t help to get rid of larvae and flies, your room will have a pleasant aroma.

Environmental Fungus Gnat Control

One way to go on the offensive with fungus gnats is to use biological controls. Introducing bacteria or microscopic worms to the soil can eradicate gnat eggs and tiny soil grubs. Let’s look at the two most common environmental gnat control methods.

Bacillus thuringiensis var. israelensis

Also called Bti, Bacillus thuringiensis is a type of bacteria that is effective in killing mosquito and gnat larvae. To use Bti against gnats, it’s important to use the right bacteria strain. For gnat larvae eradication, apply the Bt serotype israelensis.

To use bacillus thuringiensis var. israelensis for gnats, mix the liquid as per the manufacturer’s instructions. Apply the solution to your soil so that the bacteria can destroy the fungus gnat larvae. Repeat the application after two weeks.

Beneficial nematodes

Beneficial nematodes are another natural way to kill gnats in houseplants effectively. The nematodes are beneficial microscopic worms that hunt and destroy larvae in the soil. You can also introduce nematodes to the ground if you’re battling other soil-dwelling bugs.

When combining various methods to get rid of gnats for good, it’s essential to make sure that they complement each other. For example, a hydrogen peroxide drench will also kill nematodes. So, wait for two weeks after a neem oil or hydrogen peroxide flush before putting nematodes in the soil.

How to Prevent Fungus Gnats

Once you have gotten rid of your irritating fungus gnats, it is crucial to prevent them from returning. What are the best methods of avoiding fungus gnats returning to infest houseplants? Here are a few practical tips:

Control soil moisture—Always water houseplants properly. This usually means waiting until the top layer of soil is dry before watering. Also, thoroughly water plants in pots so that water drains out the container. Frequent shallow watering starves roots of moisture and creates a gnat-friendly environment.

Inspect new plants—Before bringing new houseplants home, carefully inspect them for any signs of pests. Also, isolate new houseplants for two to three weeks to protect other existing plants in your home from possible infestation.

Mulching—A layer of mulch on plant pot soil can help to prevent females from laying eggs. Just remember that mulch locks in moisture, so always check soil dampness levels before watering.

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