Skip to Content

How to Get Rid of Fungus Gnats with Hydrogen Peroxide

This article may contain affiliate links. We get paid a small commission from your purchases. More Affiliate Policy

Hydrogen peroxide is a gardener’s best friend, helping fight root rot, plant pathogens, and fungus gnats (named for their diet, not their species.)

Hydrogen peroxide is an oxidant that degrades organic compounds and is commonly used as a sterilization agent. It is so effective that even surgeons trust it to sterilize their instruments and disinfect wounds. Even our immune system produces hydrogen peroxide in limited quantities.

Table of Contents

Hydrogen Peroxide vs. Fungus Gnats

Fungus gnats (Sciaridae and Mycetophilidae families ) love moist, organically rich potting soil to lay their eggs (about 300 per gnat) close to the soil surface.

In 3 to 6 days, the eggs hatch into larvae that will bury themselves in the soil and feast on fungus, plant hair roots, and decomposing plant matter. They’ll emerge as a flying, harmless nuisance in 18 days, only to repeat the process.

Hydrogen peroxide, a common household disinfectant, is one of the most harmless and effective ways of controlling gnat larvae. The oxidative action of hydrogen peroxide (H2O2) destroys the larvae (and other microorganisms), breaking them down into water and oxygen.

The Hydrogen Peroxide Concentration Needed to Eliminate a Gnat Infestation

Hydrogen peroxide is available in a range of concentration strengths. Popular concentrations include 3, 6, 10, 12, 15, 25, 30, 32, and 34 percent. What you need is a 3% concentration of hydrogen peroxide.

Food processing plants use a 35% concentration for cleaning surface areas, which is more than ten times as strong as you need. If you have a stronger concentration, dilute it to 3%.

Before you use it to exterminate your fungi gnat larvae infestation, dilute the 3% concentration even further, mixing one part of 3% hydrogen peroxide with four parts of water. You’re left with a 0.6 percent concentration.

Don’t be tempted to double the strength in the hope that it will be more effective. The advised solution will immediately kill fungus gnat larvae upon contact, and a more concentrated solution will eliminate all soil biota and may damage your plant roots.

A three percent concentration is commonly used to treat cuts and abrasions, killing all possible pathogens (and good bacteria) and purportedly allowing the wound to heal uncompromised. There’s some debate on its wound-healing efficacy.

Using Hydrogen Peroxide to Get Rid of Fungus Gnats

Fungus gnats are a common pest of plants grown indoors, especially with high humidity and moisture. They’re usually first noticed when the harmless adults are seen flying around house plants or gathered at a nearby window.

Because these pests love moisture, one way of managing them is to allow plant soils to dry totally before applying the 0.6% solution. When you water your plants with this solution, the soil will fizz for a few minutes after application.

The hydrogen peroxide will kill fungus gnat larvae on contact. The fizzing ends briefly, and the peroxide decomposes into harmless oxygen and water molecules.

The Added Benefits of a Deep Hydrogen Peroxide Soak

Hydrogen peroxide is water with an added oxygen molecule – H2O vs. H2O2. In addition to destroying microorganisms and fungus gnat larvae, hydrogen peroxide benefits roots by boosting oxygen availability.

Hydroponically grown plants are often watered with dilute hydrogen peroxide solutions. Its natural decomposition produces oxygen that improves plant root growth and combats several pests, including root rot.

For regular watering, concentrations of roughly 0.1 percent are used; for anti-fungal effects, this can be increased to one percent. Our suggested 0.6% is somewhere in between.

Steps to Flooding your Pot Plants with Hydrogen Peroxide

Step One

Allow the pot’s soil to dry out – at least the top third of the pot’s soil should dry if you stick your finger or a dowl. Firstly, this ensures the fungus gnat larvae are more vulnerable, and secondly, it helps prevent overwatering.

Step Two

Saturate the potting soil with the hydrogen peroxide and water mixture until it freely runs out of the container’s bottom drainage holes.

Repeat the process after the pot has stood for a while, ensuring you eliminate not only all fungus gnats but also flash the soil of any accumulated salts.

Step Three

Keep the diluted solution in an airtight container and out of direct sunlight. You will need this to repeat the process when you next need to water, following steps one and two again.

Two applications will eliminate all the eggs and larvae, as their cycles are within a week.

Conclusion on How to Get Rid of Fungus Gnats with Hydrogen Peroxide

To completely eradicate fungus gnats, stop the eggs from hatching to prevent the larvae from developing. Use hydrogen peroxide to eliminate larvae at every stage. Failure to proactively fight these insects in their early stage means you’ll keep dealing with the nuisance of adults.

If you found value in this article, subscribe to the blog for all future updates. You can do that below.

[mailerlite_form form_id=5] [mailerlite_form form_id=5]