The damp potting soil of indoor and outdoor plants is a breeding ground for fungus gnats.
These tiny black flies lay eggs on the soil beds. When the eggs hatch, they produce fungus gnat larvae, which can harm the plants.
In this guide, you’ll learn the proven ways to get rid of fungus gnats, their larvae, and eggs in the soil.
You’ll also find the prevention methods to stop these pesky flies from returning.
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Let The Soil Dry
Overwatering the soil beds attracts fungus gnats. The wet soil attracts the fungus gnats to lay eggs on them.
So, letting the soil dry by not watering the plants for a few days will deter more gnats from laying eggs.
Plow The Potting Soil Inch Deep
Fungus gnat larvae dig deep into the soil to access the plants’ roots and root hair. The larvae feed on the roots, causing harm to the plants.
So, tilt the soil an inch deep to expose the hidden larvae.
Drench The Soil With Hydrogen Peroxide Solution
Mix four parts of 3% hydrogen peroxide solution with one part of water.
Use the mixture to drench the soil.
Hydrogen peroxide solution contains hydroxyl that kills fungus gnat eggs and larvae in the soil.
It also removes the molds and fungi on the soil, eliminating the larvae’s food sources.
Hydrogen peroxide also removes the molds and fungi from the soil’s layer.
That leads to better soil oxidation, positively impacting your plant’s health.
You can also use the mixture as a spray on the plants’ leaves to keep the adult fungus gnats away.
Repeat the process once a week for four weeks or till you stop noticing gnat larvae in the soil.
Alternative Ways To Kill Fungus Gnats In House Plants
The hydrogen peroxide solution is a potent fungus gnat killer. However, you’ve other options too.
Neem Oil
Neem oil is a proven natural insect killer. Use it as a spray on the soil and plants to get rid of adult fungus gnats, their larvae, pupae, and eggs.
There are neem oil plant sprays that are readily available.
Mixing neem essential oil with water can also prepare neem oil spray.
Beneficial Nematodes
Nematodes help a ton if you’re dealing with massive gnat infestations.
It will be best to use them in the yard soil beds or compost bins where flies and insects lay their eggs in large numbers.
Nematodes are parasitic worms that get inside eggs and larvae of insects.
These worms mess up with their internal systems, preventing them from maturing into adults.
Yellow Sticky Traps
Yellow sticky traps work on the adult fungus gnats rather than on the larvae.
Keep them on the soil bed of potted plants for 24 hours.
Bright yellow color draws the fungus gnats. And when these flies sit on the sticky side of the trap, they get stuck.
Dispose of the traps with gnats stuck on them the following day.
The yellow traps help prevent adult gnats from laying eggs in the soil.
Diatomaceous Earth
Diatomaceous earth is a desiccant dust penetrating larvae and insects’ bodies.
It soaks the moisture and bodily fluids in the insects’ bodies. And the insects die of dehydration.
Scatter diatomaceous earth on the soil’s surface. And let it sit for a few hours to do its work.
Then, remove the soil’s layer with dead fungus gnat larvae and dispose of it.
Dish Soap Apple Cider Vinegar Trap
Take a shallow pan or bowl and fill it half with apple cider vinegar.
Add 2-3 tablespoons of dish soap and mix it well.
Cover the pan with a plastic wrap and affix it with a rubber band or duct tape. Poke a few holes in the wrap.
Your trap is ready.
Keep the trap near the potting soil. The fruity smell of the vinegar draws the gnats.
When the gnats sneak inside the pan through the holes, they get stuck because of the sticky nature of the dish soap.
Keep the trap near the house plants’ soil for 24 hours.
Dispose of the liquid in the pan or bowl with dead fungus gnats in it the following day.
Preventing Fungus Gnats in Soil
Once you remove the fungus gnats and their larvae from the soil, you must take preventative measures to keep them from returning.
And there are a few ways to do that.
Put Sand On The Soil’s Layer
A thin layer of sand on the soil prevents the adult gnats from accessing the soil’s layer. So they can’t lay any eggs on them.
Buying Sealed Packs Potting Soil
Loose soils can contain larvae and eggs. Buy the potting soil mix that comes in sealed packages.
Heating the loose soil on a pan before using it also kills the larvae and eggs.
Drenched Mosquito Dunks On The Soil
Mosquito dunks contain BTI (Bacillus thuringiensis subsp. Israelnsis) that kills insect larvae without harming the soil.
The wet mosquito dunks release the compound in the soil, killing any larvae, adult gnats, and their eggs that may come in contact with it.
Epsom Salt
Scatter Epsom salt on the soil’s layer to kill the fungus gnats’ and their larvae. Epsom salt, like diatomaceous earth, is safe for plants and humans.
Recap
Hydrogen peroxide solution kills fungus gnats in all lifecycle stages – eggs, larvae, pupae, and adult gnats.
Other compounds are as effective as hydrogen peroxide. These are neem oil, diatomaceous earth, Epsom salt, and nematodes.
Keeping yellow sticky traps and apple cider vinegar trap near the potting soil is also a smart way to lure and trap the adult gnats.
Dr. Thomas Orbert is a PhD in Entomology with extensive research experience in ectoparasites and microbials. He has also worked in the spaces of ecology conservation and has multiple years of experience in field research and scientific publishing.