Article: Great Soil Deconstructed

Created on: Friday, April 22, 2011

Topsoil, as the name infers, is the uppermost layer of soil, usually the top 2 to 8 inches. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. The terms "topsoil" and "loam" are often used interchangeably when, in fact, not all topsoils are loams and not all loams are topsoils.
Loam is a textural classification and refers to the relative amount of sand, silt and clay in a soil. Often we expand the term "loam" to sandy loam, sandy clay loam, clay loam, silty clay loam or silt loam as the proportions of these individual soil particles change.

But let's keep it simple. Soil is the foundation of our landscape. It's comprised of sand, silt and clay, mixed with varying amounts of organic matter, water and air. It is a complex and dynamic medium, and for us gardeners, it's the plant growth medium.

For successful gardens we want topsoil rich in organic matter. When cutting new beds in your yard, you may need to begin by adding topsoil if your soil is high in sand or clay content. If you decide to purchase topsoil, be aware that there are no legal marketing standards for topsoil, so go with the rule of thumb that you get what you pay for. The more expensive products will be cleaner and have more organic matter. In most cases, purchased topsoil still requires amendments--the addition of organic matter will greatly improve the soil's physical condition. Two or three inches of organic matter tilled to a depth of 6 to 8 inches is a typical recommendation for topsoils low in organic matter.