What Is Diatomaceous Earth – Will It Kill Fungus Gnats?

Perhaps you have heard about diatomaceous earth, or someone has given you a recommendation to “use DE” to solve a pest issue, but aren’t quite sure what it is.

Very few people say diatomaceous earth, instead, they shorten it to “DE.”

The first time I heard DE I didn’t know what it stood for, and then when I found out what the abbreviation stood for, I said to myself what is diatomaceous earth? I’ve heard of diatoms before and knew they live in both fresh and saltwater, but couldn’t put together the earth part.

All the person said was that diatomaceous earth is an excellent organic pest solution to use both in the home and garden.

what is diatomaceous earth used for in the garden

What is Diatomaceous Earth?

Diatomaceous earth (DE) is a naturally occurring, very fine, soft, siliceous sedimentary rock that can be crumbled into a fine chalk-like white to off-white powder.

natural diatomaceous earth

It consists of the fossilized remains of diatoms, a type of hard-shelled microalgae. The shells of diatoms are made of silica, which is a natural substance that is also found in sand, quartz, and glass.

fossilized diatoms make diatomaceous earth

Then it made sense to me, that a die-off of diatoms could cause the shells to accumulate eventually forming a fossilized rock that can be ground into a fine-grained powder.

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Where Is Diatomaceous Earth Naturally Found?

The largest deposits of DE are found in the United States, Canada, and Europe. Other major deposits are found in Australia, China, and India.

DE is mined from the ground and then processed to remove impurities. It is then available for purchase in a variety of forms, including powder, granules, and liquids.

mining diatomaceous earth

How Does Diatomaceous Earth Work?

To humans, diatomaceous earth feels silky smooth. However, to insects, the microscopically sharp edges of the silica cause hundreds of abrasions or fine cuts that eventually desiccate and dehydrate the insects and other pests.

The sharp edges of the diatomaceous earth are like knives that cut through the insect’s exoskeleton and remove the waxy coating that protects it from drying out. This causes the insect to lose water and eventually die.

This is why DE is so effective against fungus gnat larvae, or other pests crawling in the soil.

Remember, DE is not a selective control. If an organism has a soft body or underside the DE will cut it regardless if it is friendly or not.

DE can be used to control pests in a variety of ways, including:

  • Sprinkle it on infested areas: DE can be sprinkled on floors, carpets, countertops, and other areas where pests are found. It can also be sprinkled in cracks and crevices where pests may hide.
  • Mix it with water: DE can be mixed with water to form a paste. This paste can then be applied to infested areas.
  • Make a diatomaceous earth barrier: DE can be used to create a barrier around infested areas. This will prevent pests from crossing the barrier.

Are There Different Kinds or Grades of DE?

Yes, there are a couple of different grades. There is an unprocessed grade that is only ground fine, I call that Regular Diatomaceous Earth.

Then there is Food-grade Diatomaceous Earth, which has been further processed beyond grinding.

The main difference between food-grade diatomaceous earth and regular DE is the level of crystalline silica it contains. Crystalline silica is a type of silica that can be harmful if inhaled or ingested.

Food-grade DE has a very low level of crystalline silica, while regular DE may contain higher levels.

Food-grade DE is processed to remove most of the crystalline silica. It is safe to eat and can be used as a dietary supplement or in food products.

Regular DE is not processed to remove crystalline silica and should not be ingested. It is used for other purposes, such as pest control and filtration.

With either grade, it is still not wise to breathe in the dust.

Here is a table summarizing the differences between food grade DE and regular DE:

FeatureFood Grade DERegular DE
Crystalline silica contentLowHigh
SafetySafe to eat and use in food productsNot safe to ingest
UsesDietary supplement, food products, pest control, filtrationPest control, filtration, industrial uses

If you are considering using diatomaceous earth for other uses than pest control in the soil, it is important to choose food-grade DE. This will ensure that it is safe to use and will not pose any health risks.

Regular DE is more effective against pests in the soil or pests that will crawl across it on the surface of the soil or plant.

Do not use regular DE if you spray or sprinkle it on top of microgreens or vegetables.

Food-grade DE will work, but not as effectively. If you want to use food-grade DE here are some tips for choosing food-grade diatomaceous earth:

  • Look for DE that is labeled as “food grade” or “edible”.
  • Buy DE from a reputable source.
  • Read the label carefully to make sure that the DE does not contain any harmful chemicals or additives.

Most DE is labeled “Food-grade” and here is the product I purchase, albeit in larger quantities from Harris.

If you are only using DE in the garden, here is Harris’s regular DE. More effective on bugs outside.

Is Food-Grade DE Safer to Use?

Yes, for sure, in fact, diatomaceous earth is commonly used in the food and beverage industry for grain storage and to filter beer or wine when bottling.

Is DE Safe to Use in the House?

DE is generally considered to be safe for humans when used properly. However, it can be harmful if inhaled or ingested in large quantities. It is important to follow the safety precautions when using DE.

Here are some safety precautions to keep in mind when using regular diatomaceous earth:

  • Wear a dust mask when handling DE to prevent inhaling it.
  • Keep DE out of the reach of children and pets.
  • Do not ingest DE.
  • Do not apply DE directly to the skin.
  • Wash your hands thoroughly after handling DE.

Is DE Safe For Pets?

Food-grade diatomaceous earth is generally considered to be safe for pets when used properly.

It is often fed to dogs, cats, and other pets as a natural dewormer.

However, If you are using regular diatomaceous earth to control pests in your home, it is important to vacuum it up regularly to prevent your pet from inhaling or ingesting it. You should also avoid applying it directly to your pet’s fur or skin.

uses for diatomaceous earth

Can You Use DE for Other Things?

DE has a variety of uses, including:

  • Pest control for crawling insects: DE can be used to kill insects and other pests by cutting through their exoskeletons and dehydrating them. It is effective against a variety of pests other than fungus gnats. These include cockroaches, ants, bed bugs, fleas, and spiders.
  • Pest control for foliage insects: DE can be used as an insecticide by dusting it on plants or applying it to the soil. It is effective against a variety of insect pests, including aphids, beetles, and mites.
  • Filtration: DE can be used to filter liquids and gases. It is used in swimming pools, breweries, and water treatment plants to remove impurities.
  • Absorbent: DE can absorb liquids and gases. It is used in cat litter, diapers, and oil spills to absorb moisture.
  • Polishing: DE can be used as a polishing agent. It is used in toothpaste, metal polishes, and other cleaning products.
  • Insulation: DE can be used as an insulation material. It is used in fire bricks and other products that need to be heat resistant.

Using DE to Kill Fungus Gnats

Diatomaceous earth is the best tool for killing fungus gnat larvae in the soil, or females laying eggs in the soil.

It is a natural insecticide that works by dehydrating insects. The sharp edges of the DE particles cut through the insect’s exoskeleton and remove the waxy coating that protects it from drying out. This causes the insect to lose water and eventually die.

DE is effective against fungus gnats in all stages of their life cycle, including eggs, larvae, and adults. It can be used to control fungus gnats in a variety of ways on plants other than microgreens.

  • Mix it in the soil before planting. For microgreens use around 2 to 3% by volume. You can use more for house plants.
  • Sprinkle it on the soil: DE can be sprinkled on the soil around plants where fungus gnats are found. It can also be sprinkled on the surface of potted plants.
  • Mix it with water: DE can be mixed with water to form a paste. This paste can then be applied to the soil around plants (not microgreens, though).
  • Make a diatomaceous earth barrier: DE can be used to create a barrier around plants. This will prevent fungus gnats from crossing the barrier.

To effectively kill fungus gnats with DE, it is important to apply it evenly and reapply it as needed. DE can be washed away by water, so it is important to reapply it after watering plants.

Here is an article on the best ways to prevent and control fungus gnats on microgreens.

DE Use and Microgreens

I only recommend using DE with microgreens if it is added to the soil or sprinkled on the soil surface at the time of seeding or as they come out of blackout.

Please do not sprinkle or mist it on microgreens as they near harvest. Especially if you are not using food-grade DE.

How Much Diatomaceous Earth Should You Add?

For microgreens, I recommend adding a teaspoon of DE per quart of soil. 

Remember, the home microgreen potting mix already contains DE.

If you are sprinkling it on top of the soil, I would use the same amount, maybe a little less.

For house plants, you can use more in the potting soil mix. Some people recommend adding 10 to 20% DE and 80 to 90% potting mix. This means that for a 10-gallon pot, you would need to add 1 to 2 cups of DE.

I believe this is too much. A 3% to 5% mixture by volume is more than enough. I do recommend adding more DE to house plants because more than likely you will be watering over the top of the soil and this draws more fungus gnats.

You can also use a wet application method, which is a great option if you need to apply DE to areas where dry DE won’t stick. To do this, mix four tablespoons of DE per gallon of water and apply in a thick coat to tough spots, like the tops and undersides of your plants.

It is important to reapply DE every few weeks to maintain control of pests. You should also avoid getting DE wet, as this can reduce its effectiveness.

Here are some additional tips for using DE in flower pots:

  • Use food-grade DE (to be safe).
  • Wear a dust mask when applying DE to prevent inhaling it.
  • Apply DE in a well-ventilated area.
  • Keep DE out of reach of children and pets.
  • Vacuum up DE if you spill some to prevent pets from inhaling or ingesting it.

What Bugs Besides Fungus Gnats Does Diatomaceous Earth Kill?

Diatomaceous earth (DE) is a natural insecticide that can be used to kill a variety of bugs, including fleas, mites, lice, ants, millipedes, earwigs, cockroaches, silverfish, bed bugs, crickets, centipedes, pill bugs, sow bugs, most beetles, and some grubs.

To use DE to kill bugs, you can sprinkle food-grade DE on infested areas, such as countertops, floors, and carpets.

You can also dust it on furniture, bedding, and pet bedding.

DE should be applied in a thin layer and left undisturbed for several hours or overnight. It is important to reapply DE every few weeks to maintain control of pests if you have a continual problem at home, at a camp, or in a travel camper.

Can You Use DE to Stop Snails and Slugs?

While it doesn’t kill or really harm snails and slugs they don’t like to crawl over DE, so it can be used as a protective barrier or deterrent.

My Recommendations For DE and Microgreens

Use on food-grade DE inside. Better safe than sorry.

Don’t breathe it in. Use a mask when applying DE and wash your hands, arms, and face afterward to get any dust off.

I like to mix DE in the soil instead of sprinkling it across the top. As mentioned, Home Microgreens Potting Mix already has some food-grade DE incorporated into the potting mix.


  • Todd

    Todd is the founder of Home Microgreens & the Home Microgreens store. He also writes for several other websites, including MyViewFromTheWoods.com. Todd worked at a large farm market, garden & nursery center for 20 years. Somehow he snuck off to become a geologist and professor before coming back to his senses to write & lecture about microgreens and gardening. When not at the computer, he can be found in the garden, trout stream, or mountain trail with his new Springer Spaniel Caden.

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