Diatomaceous Earth (DE) is a fine powder derived from the fossilized remains of diatoms, which are single-celled aquatic organisms. When using DE in the garden or on houseplants, select only Food Grade Diatomaceous Earth to ensure safety around people and pets. This approach focuses on controlling spider mites, tiny arachnids that damage plants by piercing leaf tissue and extracting cell contents.
Understanding the Mechanism of Control
DE provides physical pest control, unlike chemical pesticides. The powder is composed of microscopic, razor-sharp silica particles from the diatoms’ cellular structure. When a spider mite crawls across the applied DE, these jagged edges physically scratch or pierce the mite’s waxy outer layer (cuticle or exoskeleton). This damage compromises the mite’s protective barrier, which retains internal moisture.
The unique structure of the DE particles also gives them powerful absorbent properties. Once the cuticle is breached, the powder quickly absorbs the internal body fluids and natural oils, accelerating desiccation. This loss of bodily moisture leads to the mite’s fatal dehydration. Because the mechanism is purely mechanical, spider mites cannot develop resistance to Diatomaceous Earth, a common issue with chemical treatments.
Preparing and Applying Diatomaceous Earth
Effective application of Diatomaceous Earth requires thorough coverage, particularly on the undersides of leaves where spider mites congregate and lay their eggs. There are two principal methods for application. Dry dusting is the most effective method, as the powder is immediately active upon contact with the pest. Apply a very thin, even layer using a bulb duster or a fine sieve, ensuring the dust is barely visible on the foliage surface.
The second option is a wet slurry application, which is preferred for treating large plants or reaching difficult areas. To create the slurry, mix four tablespoons of food-grade DE with one gallon of water. Shake the container frequently during application, as the fine powder tends to settle quickly. The DE is not active while wet, but once the water fully evaporates, a thin, uniform residue of pest-killing powder remains bonded to the plant surface.
Reapplication is necessary because Diatomaceous Earth does not eliminate spider mite eggs, and the life cycle is short. After the initial application, monitor the plant closely and reapply the DE every five to seven days. This consistent schedule ensures that newly hatched mites are exposed before they can mature and reproduce, breaking the infestation cycle. Repeat the treatment until no signs of mites or webbing are observed.
Safety Precautions and Maximizing Results
While food-grade Diatomaceous Earth is safe for use around food and animals, its ultra-fine particle size presents an inhalation hazard. Wear a simple dust mask or respirator during application to protect the lungs from the fine silica dust. Although the powder is not chemically toxic, inhaling it can cause irritation to the respiratory system. Keep children and pets away from the immediate area until the fine particles have settled.
To maximize efficacy, Diatomaceous Earth must remain completely dry. Moisture, whether from rain, heavy dew, or overhead watering, causes the particles to clump, rendering them harmless to the mites. Avoid applying DE when rain is expected or in windy conditions that would scatter the powder. When watering plants, direct the stream only to the soil to prevent washing the protective layer off the leaves.
The treatment works best as a proactive measure or as a rapid response to a minor infestation. For severe outbreaks, consistent application every few days is necessary to target successive generations of mites. The dry powder acts as a long-lasting barrier as long as it remains intact, offering ongoing protection against new pests. Regular inspection and timely reapplication are the most important factors for achieving successful spider mite control.