Diatomaceous earth (DE) is a natural substance used in gardening for pest management. This fine, powdery material offers an alternative to chemical treatments for insect control.
Understanding Diatomaceous Earth
Diatomaceous earth is a fine, off-white powder consisting primarily of the fossilized remains of diatoms. These are microscopic, single-celled aquatic organisms with hard shells made of silica. Over time, these diatoms accumulate, forming deposits that are mined and processed into DE.
At a microscopic level, DE particles are porous and abrasive, possessing sharp, irregular edges. Only food-grade DE should be used for pest control around plants. Pool-grade DE is heat-treated, converting its silica into a hazardous crystalline form unsuitable for gardening. Food-grade DE contains less than 1% crystalline silica.
How Diatomaceous Earth Controls Spider Mites
Diatomaceous earth physically controls spider mites. The sharp, abrasive edges of DE particles cut into the waxy outer layer of the spider mite’s exoskeleton upon contact. This mechanical damage causes the mite to lose vital body fluids and moisture.
The DE then absorbs these oils and moisture, leading to dehydration and ultimately death through desiccation. Since this action is physical, spider mites cannot develop resistance to diatomaceous earth.
Applying Diatomaceous Earth for Spider Mite Control
Before applying DE, gently clean affected plants by wiping leaves or spraying them with water to dislodge some existing mites. This helps ensure direct contact with remaining pests.
For dry application, use a duster or shaker to apply a fine, even layer of DE to the plant. Dust the top and bottom surfaces of leaves, stems, and the surrounding soil where spider mites might travel or hide. A light coating is sufficient; avoid thick layers, as this can hinder plant photosynthesis.
A wet application, or slurry, can be useful for hard-to-reach areas like the undersides of leaves. Mix about 4 tablespoons of food-grade DE per gallon of water, shaking frequently as DE does not dissolve. Spray this solution thoroughly onto all plant surfaces, ensuring good coverage. The DE becomes effective once the water evaporates and the powder dries, as DE works best in dry conditions.
Safety Considerations When Using Diatomaceous Earth
Wearing proper protective gear is important when applying diatomaceous earth. Inhaling the fine DE particles can irritate the respiratory system, so wear a dust mask or respirator.
To prevent skin dryness or irritation from the abrasive nature of DE, wear gloves. Eye protection, such as goggles, helps guard against irritation. While generally considered safe for pets and children once settled, keep them away from the application area until the dust has fully settled.
DE is non-selective, meaning it can harm beneficial insects, including pollinators, if they come into direct contact. Therefore, target application only to affected plant areas to minimize impact on helpful garden organisms.
Maximizing Effectiveness and Important Tips
For diatomaceous earth to remain effective, it must stay dry and present on plant surfaces. Reapplication is necessary after watering, rainfall, or if the dust layer is disturbed, as moisture deactivates its abrasive and absorbent properties. A reapplication schedule of every 7 to 10 days for several weeks can help disrupt the spider mite life cycle, targeting newly hatched mites.
Patience is required as results may not be immediate. Thorough coverage, particularly on the undersides of leaves where spider mites often reside, is important for success. Regularly monitoring plants for signs of mite activity allows for timely reapplication. Combining DE with other integrated pest management strategies, such as regular plant washing, can further enhance control for severe infestations.