What Is Diatomaceous Earth?

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?

Slugs 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.

Caution: The downside to DE is that it does not discriminate between pests and beneficial insects. Ladybugs, green lacewings, butterflies, bees, and other "good guys" can also be killed by DE if they come into contact with it. For this reason, we recommend using DE with discretion on and around plants that beneficial insects may frequently visit. Avoid using it around flowers as well.

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.

Food-grade DE is not toxic if ingested in small quantities. 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! However, the DE that is commonly used in pool maintenance is not edible.

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.