Diatomaceous Earth (DE) is a fine, natural powder used by gardeners for non-toxic pest control. This substance is composed of the fossilized remains of diatoms, which are ancient, hard-shelled microalgae. The powder is primarily made up of silica, giving it a soft, talc-like feel to human touch. DE offers an effective, chemical-free method to manage certain insect populations in the garden.
How Diatomaceous Earth Kills Pests
Diatomaceous Earth acts as a mechanical insecticide, killing pests through physical action. The microscopic particles of the powder are sharp and abrasive, resembling tiny shards of glass under magnification. When crawling insects come into contact with the powder, these sharp edges penetrate and damage the insect’s protective waxy outer layer, known as the exoskeleton or cuticle.
This physical abrasion compromises the insect’s natural barrier against moisture loss. The highly porous nature of DE then works as a desiccant, absorbing the protective lipids and moisture from the insect’s body, leading to fatal dehydration. This mechanism is effective against a wide range of pests, including aphids, ants, mites, and slugs, and insects cannot develop resistance to it.
Consequences of Excessive Application
Using too much Diatomaceous Earth or applying it incorrectly can lead to negative outcomes for the garden ecosystem. A heavy coating of DE on leaves can physically obstruct sunlight and block the stomata, the small pores plants use for gas exchange. This interference can impede photosynthesis and respiration, hindering plant growth.
A significant consequence of overapplication is indiscriminate harm to beneficial organisms. Since DE kills any arthropod with an exoskeleton, the powder does not differentiate between pests and beneficial insects. Heavily coating flowering plants will kill pollinators like bees and butterflies, as well as predatory insects like ladybugs and lacewings. Applying the powder broadly disrupts the natural balance of the garden.
The impact of excessive DE on soil structure is generally low. However, mixing very large amounts into the soil could potentially alter its fine particle balance. Furthermore, the powder’s effectiveness diminishes significantly when it becomes wet and clumps together, making heavy or repeated applications ineffective and wasteful.
Proper Techniques for Safe Use
To avoid the negative consequences of overapplication, it is important to use the powder with precision and restraint. The goal is to apply a film that is visible, yet thin, rather than caking the plant in a thick, heavy layer. A dusting that is just enough to be walked through by a crawling insect is sufficient for the mechanical action to take effect.
Application should be targeted specifically to where pests are active, such as around the base of the stems, along the perimeter of garden beds, or on the undersides of leaves where many pests hide. To protect pollinators, avoid dusting the flowers themselves, or apply the dust late in the evening when bees are not actively foraging.
The powder is most effective when it is completely dry, so reapplication is necessary after any rainfall or heavy overhead watering. For hard-to-reach areas, a wet application can be made by mixing the powder with water and spraying it, which leaves a fine residue once the water evaporates. When applying any fine dust, wearing a protective mask is a necessary safety precaution to prevent inhalation, as the microscopic particles can cause respiratory irritation.