Diatomaceous Earth (DE) is a powdery, light-colored material obtained from geological deposits made primarily of a type of algae called the diatom. Diatom shells are made of silica, a mineral that is extracted from fresh or salt water in which the diatoms live. Accumulations of fossilized diatom shells form on the floors of bodies of water, creating the deposits. In the United States, diatomite is most plentiful in California, Nevada, Washington and Oregon. France, China, Denmark, Russia and Algeria also are home to diatomite deposits. When powdered, DE can be used for horticultural and agricultural purposes.
Diatomaceous Earth as a Plant Pesticide
When insects are sprayed or dusted directly with diatomaceous earth, the sharp-edged diatomaceous particles adhere to the insects' bodies and abrade the waxy body coverings that help the insects retain water. This causes the pests to die of dehydration.
Diatomaceous Earth as a Barrier
The powder also can be used as a barrier between a desirable plant, such as a hosta, and an undesirable predator, such as a slug. Slugs will not cross a border or collar of diatomaceous earth near vulnerable plants because of diatomaceous earth's dusty, silicaceous nature.
Diatomaceous Earth as a Repellant
Plants can be dusted prophylactically with diatomaceous earth to repel potential insect pests. This is sometimes done on the bark of fruit trees or on the roots of plants.