Hydrogen Peroxide For Fungus Gnats Guide

You’re familiar with fungus gnats if you have potted plants in your home. Fungus gnat larvae thrive on the rotting organic debris in overwatered indoor plants, and these small, flying insects enjoy eating mushrooms. Fortunately, hydrogen peroxide may be used to get rid of fungus gnats.

Fungus gnats are harmless; however, a severe infestation can be exceptionally bothersome and painful to get rid of. Fungus gnats don’t bite, but they may wreak havoc on your houseplants and garden plants. During their life cycle, female adult fungus gnats can lay up to 300 eggs.

They lay their eggs on the soil’s surface. Fungus gnat larvae graze on any organic material in the soil, including plant roots, throughout their larval stage.

fungus gnat on a leaf

With the help of a simple household item in our guide, you can see how to get rid of fungus gnats; hydrogen peroxide is such a highly effective compound. (Read Gnats Vs Fruit Flies)

By the end, you’ll have more information on how to eliminate fungus gnats and carry out a hydrogen peroxide soil drench and how you can control fungus gnats using various other methods.

How Long Does It Take For Hydrogen Peroxide To Kill Fungus Gnats?

Using hydrogen peroxide, it can take up to three weeks to deal with your fungus gnat issue. However, you need to know about the gnats themselves, such as the fungus gnat species, and where hydrogen peroxide can be helpful.

This treatment won’t do anything for flying adult fungus gnats, and it only deals with the fungus gnat larvae that live in the soil. It can, however, disrupt the life cycle of these gnats on your indoor potted plants.

Fungus gnats are divided into six separate groups, all of which are related to one another. Sciaridae, Mycetophilidae, Ditomyiidae, Bolitophilidae, Diadocidiidae, and Keroplatidae are the six families Sciaridae being the most hazardous to plants.

Sciaridae adults are harmless because their only function is to lay eggs.

The larvae chew holes in plant roots, causing high numbers of yellowing, wilting, and even death. The larvae spread fungus spores dropped by adult gnats, thus increasing the number of infected plants.

The larvae are a little bigger than the adult gnats. The larvae of fungus gnats have a black, shiny head and a white-to-clear body that can grow almost a quarter-inch long. It’s hard to find fungus gnats as they like to stay hidden beneath the soil’s surface of an infested plant.

Adult fungus gnats do not eat and exist solely to reproduce. A female fungus gnat can lay 100 to 200 eggs during her brief life. A female gnat can lay up to 40 eggs at once on the surface of damp soil, near decomposing organic materials, or closer to a plant’s stem.

The eggs will hatch and begin feeding in 4 to 6 days. The larvae will feed on any organic matter on or in the soil for 14 days.

They eat the organic materials in the soil, but in a severe infestation, they feed on a plant’s more delicate root hairs. It can comprise the plant’s roots, the crown, stem, and any plant leave close to the earth’s surface.

Larvae are usually found in the top 2-3 inches of infected soil, but you can find larvae as deep as 6 inches in potting soil and at the drainage holes of plant pots of infected plants.

The larvae stop eating after 14 days and begin their pupal stage, which will last 4 to 6 days until they emerge as fungus gnat adults.

Shortly after emerging from her pupal case, a female can mate, and the cycle begins all over again. (Learn How To Get Rid Of Gnats In Houseplants)

How Does Hydrogen Peroxide Get Rid Of Fungus Gnats?

If the infestation isn’t terrible, merely drying plants more than usual may be enough to solve the problem. If the problem is severe, you may ask, does hydrogen peroxide kill gnats? You can consider using hydrogen peroxide soil soaks, yellow sticky traps, or a mix of the two.

Be patient as the complete life cycle of a fungus gnat infestation can take many days to complete.

A hydrogen peroxide soil soak can kill the larvae of fungus gnats. Hydrogen peroxide cleans the soil and the larvae.

Plants would be unharmed, while a 4:1 ratio of water would kill fungus gnat larvae to 3% hydrogen peroxide. You can either hydrate the soil with your 4:1 water-hydrogen peroxide solution, or you can soak the pot’s base in the solution and allow the soil to absorb it.

In most houses, a bottle of hydrogen peroxide can be found in the medicine cabinet. This foamy liquid is the most effective way to get rid of fungus gnats without harming the plants or the growing medium.

Here are various ways you can use hydrogen peroxide to treat your infected plants.

1. Control Fungus Gnats on Indoor Plants with Hydrogen Peroxide

  1. If you spot flying adult fungus gnats, then you have an infestation. You can let the top couple of inches of your growing medium dry out for a day or two as you prepare your hydrogen peroxide treatment.
  2. Make a mix of one part hydrogen peroxide to four parts water.
  3. Use the mixture and water the infested plant as usual.
  4. Moist soil of every plant that has or might have fungus gnats or larvae.

When the hydrogen peroxide and water mixture come into contact with the growing media, it will foam and bubble a little, but this is typical. On touch, it kills fungus gnat larvae. After a few minutes, the hydrogen peroxide fizzing ceases and the hydrogen peroxide breaks down into harmless oxygen and water molecules.

green spray bottle

2. Control Flying Fungus Gnats with Hydrogen Peroxide Spray

Adult fungus gnats can be seen fluttering around the plant. They must be removed from vulnerable plants before laying eggs in the growing medium and spread disease.

  1. Mix one part of hydrogen peroxide and four parts of water in a spray bottle.
  2. Spray the plant leaves and stems where the adult fungus gnats are visible.
  3. Repeat as required until adults are no longer visible.

Besides this treatment, you can place yellow sticky traps around the base of the plant to trap flying adult fungus gnats.

3. Hydrogen Peroxide Soil Drench

If you have a heavy infestation of fungus gnat larvae, you can use this method of using hydrogen peroxide to kill fungus gnat larvae on infected plants.

  1. Stop watering the infected plant.
  2. Let the growing medium dry slightly.
  3. Move your potted plant to a sink or take it into the garden, where you can drench the plant with your hydrogen peroxide treatment.
  4. In a large container, mix one part of hydrogen peroxide and four parts of water.
  5. Saturate your potting soil using the hydrogen peroxide water mixture until it runs from the pot’s drainage holes.
  6. Wait 10 minutes and repeat the process.

This process can instantly kill larvae and flush the tiny dead carcasses from the growing medium. You can also flush surplus salt buildup from your growing medium from over-fertilizing the plant. To get the best results, alternate Hydrogen Peroxide treatment with Neem Oil pesticide spray. (Read What Kills Gnats)

Will Hydrogen Peroxide Get Rid of Gnats?

Hydrogen peroxide (H2O2) is one of the best natural gnat killers. Hydrogen peroxide kills fungus gnats in all phases of development: eggs, larvae, pupae, and adults.

However, it isn’t the only way of dealing with a fungus gnat infestation on infected plants.

Potting mixes containing compost/ peat moss are more affected by fungus gnats and damping off. Here are a few ways you can kill fungus gnats and larvae.



Any gnat problem can occur when you have lots of decaying organic matter in your pots. Adults lay eggs in damp soil toward the upper 1/4 inch or 1/2 of soil. You can replace this with 1/2 of sand. Sand drains quickly and stops adults from laying eggs on the dry surface.


Filling tiny jars with apple cider vinegar or a cheap beer makes an excellent trap for fungus gnats and fruit flies.

Add a drop or two of dish soap to help the gnats stick since it breaks the surface tension. Replace the lids and poke tiny holes large enough for gnats and fruit flies to enter. Place around your infected plants and flying adult gnats and insects will drown as they enter.

Diatomaceous Earth:

Another effective treatment for fungus gnats is food-grade Diatomaceous Earth (DE), which is natural mineralized fossil dust. It is non-toxic; therefore, it is safe to use in your house and the environment. As fungus gnat larvae feed, the fossilized shards pierce their skin, and they dehydrate.



Cinnamon powder is a well-proven fungicide that effectively combats damping off. Controlling fungus gnats involves killing the fungus that the larvae feed on.

To use, create a layer of cinnamon on top of your potting media on the affected plants and repeat every few weeks.

Beneficial Nematodes:

Steinernema feltiae is a nematode that can suffocate the soil if it is watered. These worm-like critters can go into the soil and release a bacterium, thus killing gnats larvae.

Although beneficial nematodes are effective, they are expensive and difficult to manage in tiny quantities.

Yellow Sticky Traps:

Light and yellow sticky traps attract fungus gnats. To catch adult flies or adult gnats, place yellow sticky traps around your plants. Stakes with sticky traps are excellent for potted plants and can prevent fungus gnats breeding once they catch the new generation.

BT – Bacillus Thuringiensis var. Israelensis:

Bt is a natural bacteria that kills a variety of worms, caterpillars, larvae, and winged insects.

Fungus gnat larvae are targeted by a pair of Bt strains such as “israelensis” or “H-14.” Fungus gnats are resistant to other Bt strains. When other measures cannot control fungus gnats, Bt-i comes to the rescue.

A cheaper solution is mosquito dunks or mosquito bits. They contain the same bacteria, although in lower concentrations. These you use in the same way and spread them across the top of your organic material in your plant pot.

Neem Oil

Neem oil, like hydrogen peroxide or Bt-i, can kill fungus gnats in infected soil. However, instead of using concentrated neem oil, you must dilute it.

Follow the manufacturer’s instructions, as they may vary depending on the supplier. Fungus gnats are killed and repelled by watering with diluted neem oil. You can also add a water and neem oil mix to a spray bottle for treating leaves where adult fungus gnats gather.

Is Hydrogen Peroxide Harmful To Plants?

Fungus gnats are challenging houseplant pests, and it’s hard to spot a fungus gnat infestation to begin with.

Fungus gnat larvae feed on the roots of potted plants, which causes plants to wither and die if the infestation isn’t addressed.

  • Fungus gnats thrive in moist, warm environments, which you need to promote seed germination. Slightly reducing the water can make the growing medium less inviting for a fungus gnat.
  • Choose healthy plants with bright hues as fungus gnats lovesick plants.
  • Before buying a plant, search for small white fungus gnat larvae moving around the roots.
  • Encourage a fungus gnat-repellent environment. Ensure your potted plants have well-drained soil, dry soil surface, and there aren’t the organic materials in the plant’s soil that fungus gnats love.

Hydrogen peroxide is safe for use on plants and can get rid of fungus and fungus gnats or even fruit flies.

With all the above treatments, you can quickly combat any fungus gnat infestations on your young plants and kill larvae before starting the next life cycle.

With a bit of vigilance, your gnat problem will be no more, and you will see these plant pests can’t infect any other plants you have around your home, and you can get rid of fungus gnats effectively.

Hydrogen Peroxide For Fungus Gnats Guide (1)

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