How to Use Diatomaceous Earth in the Garden

Natural and “authorized in organic farming”, diatomaceous earth (DE) combines the roles of repellent and insecticide, helps you get rid of slugs, caterpillars, aphids, ants pollen beetles, and moths in the garden.

Fruit trees in the orchard, plants in the vegetable garden or even ornamental plants and trees can benefit from this effective treatment of diatomaceous earth that will scare away even the most reckless of garden pests! 

Despite the fact that diatomaceous earth has many benefits, it can be a controversial topic among gardeners, and you may have heard conflicting information about its use. So diatomaceous earth must be used wisely on your plants.

If you have considered using diatomaceous earth for pest control in your garden, but not sure how, or even if it’s a good idea? we will get you covered!

We will talk about what it is, how it works, and which pests it is effective against. You’ll also find out what forms are safe to use, what precautions to take when using DE, and how to apply it in the garden.

What is Diatomaceous Earth?

What is Diatomaceous Earth?

Diatomaceous earth is a non-toxic, naturally occurring substance. DE is the ground-up, fossilized remains of the diatom, a single-celled phytoplankton with cell walls made of silica, one of the hardest substances on earth (silica is also found in sand and rocks).

Sedimentary DE deposits are found around the world in both freshwater and marine environments. DE is typically surface mined in areas where these bodies of water used to be.

DE has many applications. You’ll find it used as an anti-caking agent in stored grains, as a heat shield inside metal safes, and in swimming pool filters.

It also comes in several different forms, or grades, including food grade DE. Food grade DE is safe for garden use and approved for organic agriculture.

Any other kind of DE is dangerous for both you and your garden, for reasons we’ll discuss later in this article, and should not be used.

How Does Diatomaceous Earth Deter Garden Pests?

How Does Diatomaceous Earth Deter Garden Pests?

While DE feels like a smooth fine powder, it’s actually incredibly sharp. The diatoms that make up DE are tiny–the largest diatom species measure only 2mm long–so a human sense of touch can’t detect the glassy edges of the miniscule fossil shards that make up DE.

It’s these sharp edges that make DE an excellent form of pest control in the garden. The sharp silica edges in DE don’t harm human skin, and are imperceptible to us without a microscope. But to insects, which have exoskeletons, DE is devastating.

An exoskeleton is a hard covering, or external skeleton, that protects and supports the body of certain animals.

This is in contrast to the endoskeleton, or internal skeleton, that humans and other vertebrates have.

Insects, along with crustaceans, arachnids, centipedes, and millipedes make up the group of invertebrate animals known as arthropods.

All arthropods have an exoskeleton. This means that all insects have an exoskeleton, and therefore are vulnerable to diatomaceous earth.

When an insect is exposed to DE, the silica in the DE cuts the exoskeleton with hundreds of microscopic lacerations.

These cuts do not heal. Instead, the insect becomes dehydrated to the point of death, in a process that can take several days.

It’s literally a death by a thousand cuts.In order for DE to be effective, pests need direct exposure to DE, either by being directly dusted with the material or crawling through it while navigating the soil or the surface of a plant.

DE is considered a mechanical pesticide because no chemicals are involved and direct contact is needed.

This also means that insects cannot develop resistance to DE, so it will remain effective in your garden even with long term use.

What Types of Pest Insects Does Diatomaceous Earth (DE) Kill?

What Types of Pest Insects Does Diatomaceous Earth (DE) Kill?

Diatomaceous earth kills a wide range of garden pests including but not limited to: cucumber beetles, cabbage worms, squash bugs, tomato hornworms, mexican bean beetles, potato beetles, weevils, mites, centipedes, millipedes, and aphids.

While they appear to be soft, caterpillars, being insects, have an exoskeleton and can be killed by DE.

Snails and slugs aren’t killed by DE, but it is an effective repellent for them. They prefer not to crawl through DE as it’s abrasive to their skin and slows them down.

Earthworms are not harmed by DE, so it’s also safe to use against pests in your composting or vermicomposting bins.

Since bees and other pollinators have an exoskeleton, like all insects, direct contact with DE is fatal to them.

However, DE can be relatively safe for bees if used in moderation, and if specific precautions are taken. We will touch on this issue later on when we discuss safety.

How Long Does Diatomaceous Earth Take to Kill Bugs?

How Long Does Diatomaceous Earth Take to Kill Bugs?

This varies greatly depending on the insect species and environmental factors, such as relative humidity and temperature.

For insects such as bed bugs and ants, DE can be fatal in 24 hours. For certain types of beetles,

it can take as long as three weeks to be effective. In most cases, you’ll see results in 2-5 days.

Is DE Safe to Use?

Yes, if proper precautions are taken. 

First, you must use the right kind of DE for the garden: food grade only. Other forms of DE, such as what you might purchase to maintain a swimming pool, are toxic and harmful. The main difference in these varying grades of DE are the types and amounts of silica they contain.

Diatomaceous earth can contain two kinds of silica: amorphous and crystalline. The crystalline form is far more dangerous to the lungs.

When mined, DE naturally contains mostly amorphous silica, with small amounts of crystalline silica (about 1%).

If DE is “calcined” after mining–treated with high heat or pressure–the calcination process will cause some of the amorphous silica to convert to the crystalline form.

The resulting DE product can contain up to 75% crystalline silica. This form of DE has more industrial applications and is not appropriate for home garden use.

Exposure to crystalline silica is a known factor in lung diseases such as silicosis.

Still, food grade DE is not without risk. DE can irritate the eyes, and long term inhalation exposure could harm the lungs.

Here are some tips to keep yourself safe when using DE in the garden:

  • Wear a mask to protect your lungs.
  • Wear goggles to protect your eyes.
  • Do not apply DE on a windy day.
  • Apply moderately in a targeted area.

Precautions should be taken to protect pollinators, too. Remember, bees have exoskeletons, so direct exposure to DE is fatal for them. Follow these guidelines to use DE with bees and other pollinators in mind:

  • Apply in the evening, when bees are less active.
  • Apply a ring of DE to the soil around the plant you want to protect, where bees are less active.
  • Ideally, do not apply during the flowering stage when bees will be frequenting your plants.
  • At the very least, do not apply DE on or near the flowers.

When to Use Diatomaceous Earth

When to Use Diatomaceous Earth

Because DE does have some drawbacks, namely its risk to beneficial insects, it’s best to use DE only when necessary.

DE can be an effective way to fight an active infestation by targeting specific plants and pests.

But it’s best not to use it as a blanket preventative measure, because you might also harm the good bugs in your garden.

There are other preventative options you might consider, such as kaolin clay, which can be applied in similar ways as DE but merely repels insects instead of harming them.

Ways to to Apply Diatomaceous Earth (DE) in the Garden

Ways to to Apply Diatomaceous Earth (DE) in the Garden

There are several ways to apply DE in the garden. 

For all methods, follow these guidelines:

  • Apply DE in your targeted areas only; using too much increases the chances you will harm insects that are beneficial to your garden. Use moderation and don’t apply on a windy day. 
  • Apply DE in dry weather only, as rain and high humidity render diatomaceous earth ineffective. Slightly moist or dewy conditions are okay, and can actually help the DE stick to the soil or plants. 
  • Reapply DE after a rain. DE will continue to be effective unless it is disturbed by rain or humidity. When wet, DE loses the ability to kill pests. After a rain, DE will eventually dry out, but it tends to clump after getting wet and loses effectiveness. 
  • Reapply after disturbances of wind or traffic, which can blow it away from its intended spot.
  • Use a small scoop or duster to apply DE in a controlled way. A duster uses air pressure to puff small, even amounts of DE on the desired area. Some DE brands include a duster in their packaging, or you can find them at your local garden supply retailer or hardware store.

Using Diatomaceous Earth In the Garden

  • Sprinkle DE on the soil in a ring around the base of the plant. Make sure the ring is solid; any weak spots or holes are opportunities for bugs to crawl through and reach your plant.
  • If your plants are in containers, dust the ground around and under your pots with DE.
  • Dust or sprinkle DE directly onto pests, if possible.
  • Dust DE directly onto the plant stem and leaves, especially the underside of the leaves where insects tend to lay their eggs. Lightly misting the plants before doing this will help the DE stick.
  • Make a DE spray by mixing ¼ cup DE and one gallon of water in a spray bottle or pressure sprayer, shake well, and coat your plants evenly with the mixture. Even though it was once wet, the mix will be effective once it has dried on the plant because it is a thin, even coat of DE.

In Conclusion

Diatomaceous earth is highly effective against insect pests, but doesn’t come without risks to both humans and beneficial insects.

However, because DE can be so successful in treating a pest infestation, it’s worth having in your home garden arsenal.

If you do use DE, make sure to take the proper precautions to protect yourself and the beneficial insects in your garden.

Always use food grade DE only, and follow the best practices outlined above for using and applying DE to make your treatments as effective as possible.

Amber Noyes

Written By

Amber Noyes

Amber Noyes was born and raised in a suburban California town, San Mateo. She holds a master’s degree in horticulture from the University of California as well as a BS in Biology from the University of San Francisco. With experience working on an organic farm, water conservation research, farmers’ markets, and plant nursery, she understands what makes plants thrive and how we can better understand the connection between microclimate and plant health. When she’s not on the land, Amber loves informing people of new ideas/things related to gardening, especially organic gardening, houseplants, and growing plants in a small space.

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