Diatomaceous Earth (DE) is a fine, naturally occurring powder derived from the fossilized remains of diatoms, which are ancient, single-celled aquatic organisms. Their cell walls are primarily made of amorphous silicon dioxide, forming a siliceous sedimentary rock. When mined and ground, this rock results in a highly effective, non-chemical method of pest control. Food-grade diatomaceous earth can be safely and effectively incorporated into organic pest management strategies in the garden.
How Diatomaceous Earth Eliminates Garden Pests
The mechanism by which diatomaceous earth controls insects is physical, relying on the unique structure of the fossilized diatoms. Under a microscope, the DE particles appear as microscopic, sharp-edged shards of silica. These edges are abrasive to insects that crawl across them, though they are harmless to humans and pets.
The sharp particles physically damage the insect’s protective outer layer, known as the exoskeleton or cuticle. This abrasion compromises the waxy coating essential for the insect to retain moisture. The powder’s highly absorbent nature then draws out fats and oils from the insect’s body.
This moisture loss causes the insect to rapidly dry out, leading to desiccation and death. This mechanical action is effective against common garden pests like aphids, ants, earwigs, and slugs. Because the control method is physical, target pests are unable to develop resistance over time.
Best Practices for Applying Diatomaceous Earth
Diatomaceous earth is most effective when it is completely dry. The most common method is dry dusting, which involves applying a fine, thin layer of the powder directly to areas of pest activity. Use a hand duster, sifter, or shaker to ensure an even and light coating.
The powder should be focused on the base of plants, the soil surface, and along garden bed perimeters to create a barrier against crawling pests. For foliage pests, apply a very light dusting to the leaves, including the undersides. Avoid applying a thick layer, as it can block sunlight and interfere with photosynthesis.
An alternative is the wet slurry method, useful for treating tall plants or hard-to-reach areas. This involves mixing the DE powder with water, typically four tablespoons per gallon, and spraying the solution onto the plants. The water acts as a carrier, allowing the powder to adhere to the leaf surfaces.
The diatomaceous earth becomes active once the water evaporates, leaving behind a fine, dry residue. Reapplication is necessary after any significant rainfall, heavy watering, or dew, as moisture causes the powder to clump and reduces effectiveness. Consistent replenishment of the dry powder is important for sustained pest control.
Safety Considerations and Protecting Beneficial Insects
When selecting diatomaceous earth for garden use, choose only the food-grade variety. Pool-grade or filter-grade DE is chemically altered through calcination, resulting in a high content of crystalline silica, which is hazardous to inhale. Food-grade DE contains mostly amorphous silica and is the suitable option for use around edible plants.
The fine dust, even food-grade, can irritate the respiratory system if inhaled. Gardeners should wear a dust mask or respirator during application to avoid breathing in the particles. Wearing gloves is also advisable to prevent the powder from excessively drying out the skin with prolonged contact.
Diatomaceous earth works non-selectively on any insect with an exoskeleton, meaning it can harm beneficial insects and pollinators like bees and butterflies. To minimize this risk, avoid applying the powder directly onto flower blooms. Apply DE in the late evening or very early morning hours when most pollinators are inactive. Targeted application, focusing only on areas where pests are present, helps protect non-target organisms.