Gardeners are often given the advice to sprinkle diatomaceous earth (DE) around plants to deter pests. Not surprisingly, we’re asked, “What is Diatomaceous Earth?” We’ll explain …
What is DiaTOmaceous Earth?
Diatomaceous earth (DE) is actually 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.
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, and on those with hard shells too such as beetles, fleas, cockroaches, and even bed bugs. Since it is non-selective, it can harm good bugs as well as the bad guys.
How to Use DE
Deep deposits of diatomaceous earth are mined in the western United States in places where lakes once covered the area millions of years ago. When shopping for it, look for “food grade.” The DE used in pool filters is not effective against garden pests.
Sprinkle bands of it around the plants you are trying to protect or for another level of pest control you can dust the leaves of a plant, for example, potatoes that are infested with potato beetle larvae.
DE works best when dry, even morning dew will lessen its effectiveness, so you will have to 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, this product 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.