Soil mites are tiny arthropods that naturally inhabit the soil of both outdoor gardens and indoor potted plants. They are generally microscopic, making them difficult to spot until their population becomes large. Their presence often indicates a soil environment rich in organic matter and moisture. Before attempting eradication, determine if the mites are causing harm, as many species are not pests. This initial assessment prevents unnecessary treatments that could harm beneficial organisms.
Identifying Soil Mites and Assessing Harm
The first step in managing a soil mite population is to distinguish between beneficial and potentially damaging species. Beneficial mites, such as Oribatid mites, are typically slow-moving, round, and dark brown decomposers that break down organic matter and cycle nutrients back into the soil. Other beneficial predatory mites, like Stratiolaelaps scimitus, are tan, pear-shaped, and move quickly across the soil surface as they hunt pest larvae. These mites are a sign of a healthy soil environment and require no control.
Harmful soil mites, which are less common, include certain root-feeding Prostigmata mites or bulb mites that feed on tender roots and root hairs. An infestation is often indicated by the plant showing signs of distress rather than the mites themselves. Look for symptoms such as stunted growth, yellowing or wilting leaves, and a general decline in health not attributable to watering issues or nutrient deficiencies. Inspect the soil surface, or gently tap the plant out of its pot to examine the rootball for tiny, clustered white or light-colored mites feeding directly on the roots.
Non-Pesticide Control Through Environmental Adjustment
If the mites are harmful or their sheer numbers are a nuisance, environmental controls are the least invasive starting point. Most soil mites thrive in high-moisture conditions and feed on decaying organic material. The most effective action is to allow the soil to dry out significantly between waterings, making the habitat inhospitable. This practice drastically reduces the population by eliminating the excessive moisture they need to flourish and reproduce.
Sanitation is another practical measure. Remove any decaying organic matter, such as fallen leaves or old mulch, from the soil surface. This reduces the mites’ primary food source, starving the population and discouraging further colonization. For potted plants, physical removal of the infested medium offers immediate relief. Scrape off the top inch or two of soil, where many mites congregate, and replace it with a fresh, sterilized potting mix.
For a severe infestation, completely repotting the plant may be the only non-chemical option. Carefully remove the plant from its container and gently wash the roots under lukewarm water to remove all traces of the old, infested soil and any clinging mites. The plant should then be placed into a clean container with entirely new, sterilized potting mix, ensuring the old pot is thoroughly cleaned with a mild soap solution before reuse.
Targeting Mites with Biological and Chemical Treatments
When environmental adjustments fail to control a problematic soil mite population, specific treatments can be introduced.
Biological Control
Biological control involves introducing predators, such as the mite Stratiolaelaps scimitus, directly to the soil. These predatory mites actively hunt and consume the larvae of various soil-dwelling pests, including fungus gnats and thrips. Another biological option is the application of beneficial nematodes, which are microscopic roundworms that parasitize and kill soil pests, though their effectiveness varies depending on the target mite species.
Chemical Treatments
Chemical treatments should be considered as a last resort, starting with less harsh organic options. Neem oil, diluted and applied as a soil drench, offers systemic control, as the plant absorbs the active compound, azadirachtin. This compound acts as a feeding deterrent and growth inhibitor to soil-dwelling pests that ingest the plant’s sap. For a current infestation, a neem oil drench is typically reapplied weekly until the population is under control.
Insecticidal soap, formulated with potassium salts of fatty acids, can also be applied as a soil drench to target soft-bodied pests like root mealybugs and some mites. This treatment works on contact, disrupting the pest’s cell membranes and causing dehydration, but requires thorough saturation of the soil. For severe infestations, stronger synthetic miticides are available. These products are specifically formulated to kill mites and often come with warnings regarding their impact on beneficial soil organisms and the environment. They should only be used strictly following the label instructions and when all other non-chemical and organic control methods have proven unsuccessful.