The words "loam" and "topsoil" are often used interchangeably to refer to rich soil used to improve rocky or infertile soil, but there are some important distinctions between the two terms.
Topsoil or Loam?
Topsoil refers to any type of soil that makes up the upper layer of soil. Loam is used to describe the texture of soil. Loam can be topsoil, but not all topsoil is loam.
Topsoil is the result of organic matter decaying and rocks weathering over hundreds of years. Organic matter usually comprises between 2 and 10 percent of topsoil, resulting in it being darker in color than the subsoils.
Loam consists of clay, sand and silt. The best loam is about 25 percent clay, 25 percent silt and 50 percent sand. That composition allows loam to hold enough moisture for plants, while still draining adequately for air circulation.
Loam Is Best Topsoil
Loam is the best topsoil because of its composition. Large particles of sand provide good aeration, while small pieces of clay hold moisture. Silt is smaller than sand, but larger than clay, and has the properties of both. Loam may be called sandy loam, silty loam or clay loam, depending upon the proportions of each component.
Topsoil should be bought from a reliable vendor. A soil test should be done to determine the pH and soil texture. Topsoil should contain organic matter, but should not include any rocks, trash or debris. If putting soil in your garden, also make sure it is relatively free of roots and seeds of noxious weeds, particularly ground ivy and crabgrass. It should have a fresh clean odor---not sour or chemical-like.
Topsoil can be amended to make it more like loam. Heavy clay soils can be mixed with sand and silt, while sandy soils can be amended with clay. These techniques can be labor-intensive and work best for relatively small areas, such as garden beds.
- University of Connecticut Extension
- Purchasing Topsoil
- What Is Loam
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About this Author
Melody Lee worked as a newspaper reporter, copywriter and editor for 5 years. In addition, she has edited magazine articles and books. Lee holds a degree in landscape design and is a Florida master gardener. She has more than 25 years of gardening experience, which includes working at nurseries and greenhouses.