Does Diatomaceous Earth Control Fungus Gnats

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Let’s start by asking: Will Diatomaceous Earth kill Fungus Gnats? Face it, nobody wants flies in their house, especially tiny gnats. Unfortunately, this is a common risk when you have houseplants. Let’s answer the question.

Fungus gnats are small, black bugs that look like tiny mosquitoes with long, thin antennae. They belong to a big group called the Sciaroidea and eat mostly fungus.

fungus gnat larvae feeds in plant soilPin

They often infest overwatered house plants or ones in very moist conditions. Gnats also show up in plants infested by other pests, such as aphids.

The real problem lies in their habit of nibbling on your plants’ roots while foraging for fungus.

As the larvae like to burrow into the wet plant soil, a lot of popular pest control methods won’t work.

But what about the classic soil remedy, diatomaceous earth for fungus gnats?

In this article, we’ll explore every facet of diatomaceous earth and fungus gnats, including how to use diatomaceous earth for fungus gnats.

Does Diatomaceous Earth Kill Fungus Gnats?

Diatomaceous Earth (DE) is an efficient, safe, and non-toxic solution for addressing fungus gnat infestations in your plants.

To apply DE, evenly sprinkle a generous layer on top of the soil or mix it into the potting soil before repotting your plant.

This eco-friendly powder targets both larvae and adult gnats by causing rapid dehydration and eventually eliminating the infestation.

The good news is diatomaceous earth (or DE for short) is an effective remedy against fungus gnats.

The bad news is you’ll still have the little buggers flying around for a week or two.

What is Diatomaceous Earth?

Diatomaceous earth (or DE) is a safe and natural way to get rid of pests. It’s not harmful and is found in nature.

It’s made from the crushed fossils of diatoms, a prehistoric, microscopic lifeform. DE has been used as an effective deterrent for rodents and is a natural killer of insects and arachnids (spider mites).

DE is tiny and feels like smooth sand or powder to us, but it feels like sharp, broken glass for soft-bodied bugs.

The sharp, fossilized shell fragments slice the bug’s exoskeleton. This causes the pest to leak bodily fluids until they dehydrate to death.

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Fungus Gnat Larvae: The Real Threat

Adult fungus gnats are only a danger to your sanity. The ability of an adult female to lay up to 200 eggs can create a more severe problem.

The female lays the eggs in the top layer of soil during the single week she’s alive.

These fungus gnat eggs then hatch, and the larvae burrow down into the soil.

Once there, the larvae feed on any fungus or organic matter, including plant roots.

Left unchecked, one female fungus gnat adult can quickly cause a gnat population explosion.

But, to fight the true threat, you must treat the soil during the larval stage.

This is where DE comes in.

Using Diatomaceous Earth to Kill Fungus Gnat Larvae

Always use food-grade diatomaceous earth when treating plants. Pool grade DE contains toxic levels of silica.

Allow the soil mix to dry out before applying the DE, as it loses its effectiveness when wet.

Once the growing medium has had a chance to dry, sprinkle a layer of DE directly onto the soil, giving it a thin dusting.

When adult Fungus gnats land on the soil surface, or the young larvae try to come out of the soil, the DE cuts them. These cuts will soon cause them to die.

Some plant lovers suggest putting diatomaceous earth for gnats under a pot or container. This helps stop bugs from coming in through the small drainage holes.

DE only works on the fungus gnats when they try to come out of your plant’s soil. Getting rid of all the fungus gnats might take some time.

Diatomaceous Earth Fungus Gnats: Aftercare and Prevention Methods

Fungus gnats usually appear for one of two reasons:

  • Excessive moisture
  • Existing infestations

Treat your plants regularly with preventative measures like:

  • Neem soil soaks
  • Neem Oil foliar sprays

Piercing insects such as aphids and scales will leave behind partially digested sap known as honeydew.

This honeydew attracts ants and leads to fungal infections such as sooty mold if not cleaned up.

Isolate Plants With Fungal Infection

Isolate any plants that have a fungal infection. The fungus or mold itself may not transfer to other plants but will attract fungus gnats.

The gnats will lay their eggs on the affected plant and others nearby.

Overwatering can lead to root rot, a common infection, bacterial or fungal in nature.

Root rot draws fungus gnat larvae to the roots, where they’ll do even more damage than the rot alone.

Only water your plants when needed. Use the finger method to test when a plant actually needs watering.

Bacillus thuringiensis (Bti) Naturally-Occurring Bacteria 

To effectively kill these pests, apply the naturally-occurring bacteria like Bacillus thuringiensis (Bti). Mosquito dunks (mosquito bits) containing the bacteria will also work well.

Also, you can use yellow sticky traps around the plant. These traps can catch adult gnats before they get a chance to mate.

Related: Learn To Make A DIY Gnat Trap For Plants

Hydrogen Peroxide Solution


  • 4 parts water
  • 1 part hydrogen peroxide

Water your plants with the solution to kill these pests while eliminating fungi and mold. 

Dish Soap and Apple Cider Vinegar

A mixture of dish soap and apple cider vinegar is another great way to kill them.

More on How To Get Rid of Gnats in Houseplants with Vinegar

Nursing Plant Back To Health

Finally, your plant may be under the weather after the infestation is gone. Make sure to:

  • Place it in a location where it can get the ideal conditions (light and temperature).
  • Fertilize properly during the recovery process.

You may choose to dust the plant with some DE as another preventative occasionally. Remember that dusting will be washed away at the next watering or rainfall.

Remember, fungus gnats have a fast life cycle. It is important to control their population and reduce their numbers before severe infestation.

FAQs On DE for Fungus Gnats

How Long Does it Take Diatomaceous Earth to Kill Fungus Gnats?

Diatomaceous earth can kill fungus gnats within a few days to a week. How fast depends on the severity of the infestation and the application method.

How Much Diatomaceous Earth Do I Use for Fungus Gnats?

The amount of DE needed to control fungus gnats will depend on the affected area’s size and the infestation’s severity.

As a general rule, sprinkle a thin layer of DE over the soil surface. Focus on areas where the fungus gnats are most active.

How Often Should I Sprinkle Diatomaceous Earth?

To effectively control fungus gnats, sprinkle DE on the soil surface every 2-3 weeks. Try to maintain a thin layer of powder.

Reapply Diatomaceous Earth after watering or heavy rainfall. Moisture can reduce its effectiveness.

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