What Is Sterile Soil?

Sterilized Soil

• Sterile or sterilized soil (used interchangeably) has been chemically or heat-treated to prevent harmful pathogens from harming plants. The logic behind this is that these pathogens might be present in the soil, so all microbial organisms are killed off, effectively sterilizing the soil. Chemicals are used to fumigate the soil, while heat-based sterilization relies on cooking the soil in an oven or microwave, or solarizing the soil by spreading clear plastic over it during the summer and letting direct sunlight blast the soil with heat and ultraviolet rays.

Applications

• Seeds and seedlings in particular are susceptible to damping-off, a soil-borne disease that kills the germinating plant before it has the chance to resist. House plants and other potted plants are grown under conditions where many pathogens and pest insects that spread pathogens aren't exposed to natural predators. So they often go unchecked if they are already present in the soil. In other cases, outdoor soil has been exposed to a disease that may stay in the soil for years. Sterilizing the soil before planting anything in such soils may help reduce disease and pest problems.

Problems

• Sterilizing soil removes not only the pathogens, but also the predator microbes that would normally keep the pathogens in check. It also alters the structure and chemical makeup of the soil and kills beneficial microbes that work in symbiosis with the plant. At best, they are a temporary solution, since pathogens travel by air, by flying insects, and on the surface of humans or animals that come in and out of the area.

Unproductive Soil

• Soil that is unable to support plant life, or very little of it, is also called sterile soil. Not only are essential microbes missing, but there are also precious few nutrients in the soil. Climatic conditions, such as little to no moisture or constant sub-zero temperatures usually accompany the environment of sterile soil. However, soil that has been over-tilled, over-fertilized and overloaded with pesticides can become sterile as well, since chemical nutrients of fertilizers alone are only sufficient in such an overworked area if they are constantly applied. Overworking the soil has the seemingly ironic effect of depleting it.