Diatomaceous Earth (DE) is a naturally occurring, fine, powdery substance composed of the fossilized remains of microscopic aquatic organisms called diatoms. These ancient algae left behind shells made of amorphous silica, which is mined and processed into a mechanical insecticide. The powder works by physically damaging the waxy outer protective layer, or exoskeleton, of insects, causing them to lose moisture and ultimately die from dehydration. Because its action is physical rather than chemical, pests cannot develop resistance to it, making it a sustainable, non-toxic option for managing household and garden insects, provided the powder stays dry.
Preparation and Safety Gear
The first step in safe application involves selecting the correct type of product, which must be labeled as “Food Grade” diatomaceous earth. This designation ensures the product contains less than 1% crystalline silica, which is the form that poses a respiratory hazard to humans and animals. “Filter Grade” or “Pool Grade” DE, which is heat-treated, contains higher levels of crystalline silica and should never be used for pest control around people or pets. Even with the safer Food Grade product, proper safety equipment is necessary because inhaling any fine dust can irritate the lungs.
When applying the powder, wear a dust mask or a respirator to prevent the inhalation of airborne particles. Eye protection, such as goggles, will shield the sensitive eye membranes from irritation. It is also advisable to wear gloves, as the powder’s highly absorbent nature can cause drying and irritation to the skin. Applying the product in a well-ventilated area, or ensuring the air conditioning and heating systems are off indoors, helps minimize the risk of respiratory exposure.
Targeted Application Inside the Home
The effectiveness of DE indoors relies on a light, virtually invisible application in areas where pests travel. A thick layer of powder is counterproductive because insects will detect and walk around it. Instead, the goal is to create a fine coating that pests cannot avoid, ensuring the microscopic particles make contact with their bodies.
Tools like a bellows duster, a dedicated powder applicator, or even a soft paintbrush should be used to disperse the powder. Focus the application on hidden, protected areas, such as behind and under appliances, along the rear edges of baseboards, and into cracks and crevices. These locations are often frequented by crawling insects, and the powder is less likely to become airborne from foot traffic or air currents.
You can also lightly dust inside wall voids through electrical outlets or plumbing entry points, creating a long-lasting barrier in inaccessible spaces. For treating carpets or pet bedding, a light sprinkling can be left for 12 to 48 hours before being thoroughly vacuumed up. The powder remains effective indefinitely in dry, undisturbed indoor environments, continuing to kill pests that cross the treated areas.
Broad Application for Yards and Gardens
Outdoor application requires consideration of environmental factors, as DE loses its effectiveness when it becomes wet. The powder acts best as a dry physical barrier around the perimeter of the home or garden beds to deter slugs, snails, and crawling insects. Using a hand duster or flour sifter allows for an even, thin layer of powder to be applied directly to ant mounds or along the foundation of the house.
When creating a perimeter barrier around plants, ensure the DE forms an unbroken, fine line that insects must cross to reach the foliage. Wind can easily scatter the dry powder, so application should be done on calm days or in the early morning when dew may help the dust adhere to the ground and plants. If the treated area is exposed to rain, heavy dew, or overhead watering, the DE will clump and become ineffective, necessitating immediate reapplication once the surface dries.
For treating plant foliage, particularly on hard-to-reach areas like the undersides of leaves, a wet application, or slurry, is often utilized. A slurry can be prepared by mixing approximately four tablespoons of food-grade DE with one gallon of water. This mixture must be shaken frequently during application, as the DE particles will rapidly settle at the bottom of the sprayer. The DE only becomes active as an insecticide once the water evaporates, leaving behind a fine film of powder on the plant surfaces.
Monitoring and Cleanup
Once the DE has been applied, monitoring the treated areas for several days is necessary to confirm pest activity is decreasing. The mechanical action of the powder typically causes insects to succumb to dehydration within 24 to 72 hours of contact. Since the powder remains effective as long as it is completely dry, indoor applications in protected areas may not require cleanup for months or even years.
For visible indoor surfaces like carpets, counters, or furniture, cleanup is necessary after the treatment period has passed. A vacuum cleaner with a high-efficiency particulate air (HEPA) filter or a shop vacuum is recommended for removing the abrasive powder from soft surfaces. The fine silica particles can damage the motors and clog the filters of standard household vacuums.
For hard surfaces, the powder can be easily wiped away using a damp cloth or mop. Wetting the DE renders it inactive as a pesticide and prevents the fine particles from becoming airborne during the cleaning process. Any cloths or vacuum contents containing the powder should be sealed in a plastic bag before disposal to avoid reintroducing dust into the air.