What is Diatomaceous Earth?

Using Diatomaceous Earth in the Garden

Jul 26, 2018
Diatomaceous Earth

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Gardeners are often given the advice to sprinkle diatomaceous earth (DE) around plants to deter pests. Unsurprisingly, we’re often asked, “What is diatomaceous earth, exactly?” Well, here’s your answer…

What is DiaTOmaceous Earth? 

Diatomaceous earth (DE) is the fossilized skeletons of microscopic single-celled aquatic organisms called diatoms. Their skeletons are made of a natural substance called silica—which makes up 26% of the Earth’s crust by weight. 

Deep deposits of diatomaceous earth are mined in the western United States in places where lakes once covered the area millions of years ago.

How Does DiaTOmaceous Earth Deter Garden Pests?

Snugs and snails do not like to crawl over DE because the silica skeletons are very sharp—like tiny pieces of broken glass. (Slugs and snails don’t like eggshells either!) If their soft bodies do get cut, they eventually dehydrate and die. This process works on other soft bodied insects, too, including caterpillars and aphids, as well as on those with hard shells, such as beetles, fleas, cockroaches, and even bed bugs. The tiny particles of DE get into the insects’ joints, causing irritation and dehydration.

The downside to DE is that it does not discriminate between pests and beneficial insects. Ladybugs, green lacewings, butterflies, bees, and other “good guys” will also be affected by DE.

How to Use DE

  • When shopping for DE, look for the “food grade” quality. The DE used in pool filters is not effective against garden pests.
  • Sprinkle bands of DE around the plants you are trying to protect. It’s important that the ring of DE does not have any gaps for pests to sneak through. 
  • If pests are eating the leaves of your plants, you can dust the leaves with DE, which should discourage further damage. However, you should avoid applying DE near the plants’ flowers, where pollinators might inadvertently come into contact with it.
  • When using DE, it’s recommended to wear eye protection and a dust mask, as the small particles can be irritating.
  • DE works best in dry conditions. It clumps together when wet, so reapply after it rains.

Is DE Safe to Use?

Even though the industry states that this product does not cause lung damage, I would still refrain from breathing it in. Remember, it might feel soft to the touch, like talcum powder, but it still is an abrasive and can cause irritation to your eyes, nose, lungs, and throat. Wear a dust mask and eye protection when handling it just to be on the safe side.

Surprisingly, DE is not toxic if eaten! In fact, we probably have been eating it for years unknowingly, since it is often mixed with grain in storage to kill insects. It can also be found in toothpastes and skin care products. Some people take it a step farther and use it for treating internal parasites! 

DE does not harm the soil since it is made from silica, the same as sand and many rocks. It does not break down when exposed to sun. Rain can wash it into local water sources but it is non-toxic to fish and other aquatic life. It is not harmful to birds or other wildlife. It has been added to livestock feed for years.

If pests are enough of a problem that you would be tempted to resort to a chemical pesticide, give DE a try first. It is considered organic by the Organic Materials Review Institute (OMRI) and the National Organic Program considers it a non-synthetic and permits it use in crop production.

See the Almanac’s Pests and Diseases Library for more advice on solving gardening problems.

About This Blog

Get inspired by Robin Sweetser's backyard gardening tips. Robin has been a contributor to The Old Farmer's Almanac and the All-Seasons Garden Guide for many years. She and her partner Tom have a small greenhouse business and also sell plants, cut flowers, and vegetables at their local Farmer's Market.

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Reader Comments

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DE Uses

We used it to get rid of bed-bugs in our home. Also, any invasive bugs that crawl into our home.

Does DE kill iris borer?

I have heard that DE kills iris borer. If so, how is it applied?

Sprinkle it around the

Sprinkle it around the rhizomes in early spring when the caterpillars hatch out and go looking for iris foliage to eat or in late summer when they leave the dead rhizomes and head for the soil to burrow in and pupate over the winter. Finely ground eggshells will work too.

Diatomaceus earth

I wanted a natural pest control for my yard this year. I bought food grade DE. The directions said to mix it with water and spray it on. It killed every bug within yards of my property. The bees were gone unfortunately, flies and knats were gone, and it killed all the blossoms on my azalea bush. I also started getting ants on my kitchen counter and sprayed a little of it around my outside foundation and haven't seen an ant since. I will use it again, but more spareingly. I don't want to kill the good insects and bees.

DE is an indiscriminate

DE is an indiscriminate killer so beneficials will be killed along with the bad bugs. You need to use it sparingly. To lessen the impact on bees and other pollinators, avoid spraying it in or near blossoms. Apply it in the evening when most pollinators are not active. If it was applied heavily to your azalea blossoms it probably dried them out.

Effective Horn Worm Combatant

Our tomato plants were overrun with horn worms this year, so we tried diatomaceous earth before resorting to chemicals; it worked great—saved our crop this season. Highly recommend!

D.E.

There are outcrops of DE along roads in my neck of the woods. I'm guessing the raw product from these outcrops is just as good our better than the store bought?

Maybe not. The finer food

Maybe not. The finer food grade DE is the most effective.

Safe for cats?

I just saw a video which recommended sprinkling catnip on D.E. to lure cats into rolling in it. The D.E. is supposed to destroy fleas. But this article warns against the potential hazards of airborne D.E. and its affect on lungs. Is this safe for cats or not?

Food grade DE has smaller

Food grade DE has smaller particles and lower silica content. It is the silica that eventually damages your lungs. I always err on the side of caution which is why I would recommend that you wear a mask when using DE just in case. Many pet owners swear by it for flea control on their cats and dogs. It does dry out their skin so it is also recommended that you bath them after a few days to wash it off. I have never tried bathing a cat, have you?

Diatomaceous earth

My container of DE said to mix it with water and spray it on my plants and underneath them. It got rid of every bug, flying and crawling, in my whole yard. I had ants getting into the kitchen through the outside wall. I sprayed it outside of the wall and haven't seen an ant since. One caveat, don't spray it on flowers or blossoms. It kills them too.

DE

Had some house guests who had recently moved to a new apartment. Unbeknownst to them, their new apartment had bed bugs. Needless to say, by the time they left our house, we had bed bugs too. Had the exterminator out three times at a cost of well over $300, all to no effect. The bed bugs persisted. Got some Diatomaceous Earth, and spread it in all out dresser drawers, around all the baseboards, and around the headboard of the bed. (Bed bugs nest in wood, and only get into beds to feed on teh people sleeping there.) We left the DE there for four weeks (bed bug eggs gestate for three weeks), and have not had an issue since.

DE

Will it kill stink bugs? They have been terrible this year in my garden, and I am just thinking about how to have a better crop next year! Thanks!

Crushed Egg Shells

If you grind your eggshells up you save from your chickens you can make your own diatomaceous earth for free!!!! (:

DE

A few weeks ago when I was inspecting my cabbages (green & red), broccoli, and Brussel sprouts, I noticed the green cabbages in particular looked like swiss cheese. I quickly bought (non food grade) DE and sprinkled it with a sifter from the dollar store. It works. It stopped the damage almost instantly. I've since decided to use only food grade so the local cats don't get sick even though I have most of my plants surrounded with chicken wire. When my fall lettuce starts growing I'll use it on this to as this summer I was plagued with cinch bugs. I'm so happy I saw the article on DE from the old Farmer's Almanac. Thanks to all.

DE non food grade

More a question than a comment. Does non food grade do any good against insects and why would it lose it's usefulness by getting wet? Does it loose it's silica or would it return to it's natural form when it dries? I am in Texas so I want to use it in the house as well as the garden.

The non-food grade is not

The non-food grade is not recommended because it has been subjected to high heat which changes its silica into crystalline silica which can be harmful to humans and pets. That is why it is only used for filters. Food grade is called amorphous silica. Since DE works by cutting thru the exoskeleton of an insect and drying it from the inside out it is not going to be as effective when wet. After it has dried out it will be effective again. It is recommended to reapply if it gets washed away.

DE

Caution, wonderful product, but have heard it is harmful to bees, so research safe usage more.

It is recommended that you

It is recommended that you not sprinkle DE on the blossoms of your plants to prevent bees from coming in contact with it.

De

I have used de for years with no issues to the bees. All of my animals eat it from the fish to the horses, people included, it have loads of benefits the list ia just too long to post here!

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