Diatomaceous Earth (DE) is a naturally occurring substance often used as a non-toxic insecticide in homes and gardens. This fine, white powder consists of the fossilized remains of ancient, aquatic organisms called diatoms. The primary component is amorphous silicon dioxide, a form of silica. The widespread concern among homeowners is whether this effective pest control method will also damage their established lawn.
The Direct Answer: Effect on Grass and Plants
The direct answer is that Diatomaceous Earth does not kill grass, shrubs, or other established vegetation when applied correctly. The food-grade form of DE is inert when it comes to plant biology. Unlike chemical herbicides that interfere with plant growth or metabolism, DE does not possess any phytotoxic properties that would harm turf.
Plants have robust structures, including cell walls and waxy cuticles, that are completely unaffected by the physical action of the silica dust. Plants absorb nutrients through their root systems and foliage in a way that is not disrupted by the presence of the mineral powder on the surface.
Understanding DE’s Mechanism of Action
Diatomaceous Earth is an effective insecticide precisely because its mechanism is physical, not chemical. Under a microscope, the silica particles resemble tiny, jagged shards of glass, though they feel like a soft powder to human touch. This microscopic structure makes the substance deadly to insects while being harmless to plants and mammals.
When a crawling insect moves across the powder, the sharp edges of the DE particles cut into its protective outer layer, known as the exoskeleton or cuticle. This protective layer is coated in waxy lipids crucial for moisture retention. Once the exoskeleton is breached, the highly porous silica dust begins to absorb the insect’s internal oils and moisture.
This physical process leads to rapid water loss, a condition known as desiccation, which ultimately kills the pest. Because plants do not have a hard exoskeleton or similar external structure, they are structurally immune to this mechanical action. The physical nature of the process also means that insects cannot develop resistance to it over time.
Proper Application for Lawn Pests
For effective pest control on a lawn, it is necessary to use the food-grade version of Diatomaceous Earth, as the pool-grade variety is chemically treated and unsuitable for yard use. The most crucial factor for success is ensuring the product remains dry, as the abrasive and absorbent mechanism stops working when the powder is wet or clumped. It must be reapplied if the lawn experiences heavy rain or significant morning dew.
The powder should be spread as a very thin, almost invisible layer across the turf, focusing on areas where pests are known to travel or congregate, such as ant mounds or along the perimeter of structures. Using a dust applicator or a fine spreader helps achieve the necessary even and light coverage. Application should occur on a windless day to ensure the fine dust settles precisely where needed.
Wet Application
Some users opt to mix the powder with water and apply it as a spray solution, which can help it adhere to hard-to-reach areas. However, the water must fully evaporate for the DE to become active and begin its physical action against the pests. Applying the dust in the early evening is often recommended to minimize exposure to beneficial insects like bees, which are less active during those hours.