Tips for purchasing the best topsoil
By Dawn Pettinelli - UConn Home & Garden Education Center
Feature Article - posted Fri., Apr. 22, 2011
Often, a new landscape project around the home requires the purchase of topsoil – or so one is lead to believe. A common misconception when buying topsoil is that the soil we receive will be a dark, friable, fertile loam able to cure any or all garden ills. In reality, there are no legal marketing standards for topsoil. To confuse matters even more, the terms “topsoil” and “loam” are often used interchangeably when, in fact, not all topsoils are loams and not all loams are topsoils.
Soil, the foundation of our landscape, is composed of sand, silt and clay, with varying amounts of organic material, water and air mixed in. It is not a uniform material and may exhibit differences in composition or properties even over distances of a few feet. Typically, when problems arise in the home landscape, soils bear the brunt of the blame when often environmental, cultural or biological factors may be causing the plant’s demise.
So how do you know when to buy new topsoil and when to either amend your present soil or adjust your cultural techniques? There is no hard and fast answer. As a rule, purchased topsoil is necessary to adjust the grade of the landscape, to create raised beds or possibly to cover existing soils having high lead levels. If your soil is infertile, acidic or difficult to work, the additions of limestone, organic matter and nutrients will do much to improve its condition. Locally-obtained topsoil is often not too different from what you presently have on site. Bagged topsoil may be pH balanced and well fortified with organic matter and/or nutrients, but it would be an expensive way to fill in a large area.
“Topsoil” is defined as the uppermost layer of soil. It is usually darker in color than the subsoil below because of the accumulation of organic matter. Virgin topsoils in Connecticut range up to 5 inches or so thick. Since most soils in the state have been disturbed or cultivated at one time or another, a more functional definition of topsoil would be the depth of soil that ordinarily would be mixed by normal cultivation practices, in most cases 6 to 8 inches.
The term “loam,” on the other hand, is a soil textural classification. Texture refers to the relative amounts of sand, silt and clay-sized particles occurring in a soil. By USDA definition, a loam is any soil with between 7 and 27 percent clay, less than 52 percent sand, and the rest silt. The term “loam” would be further modified to sandy loam, silty loam, etc., as the proportion of the individual soil separates change. In Connecticut, sandy loam soils are quite common, with loams and silt loams typically developing along waterways and coarser loamy sands along the coast.
Before you purchase any topsoil, it is a good idea to visually inspect the stockpiled soil. It should be free from glass, trash and other debris. Pick up a handful and moisten it. Rub a small amount between your thumb and forefinger. If it feels mostly gritty, it contains a fair amount of sand. A soft, floury feeling indicates a silty soil, and if it is sticky and easily molded, it probably has a high clay content. Many consider a sandy loam soil, with about 5 percent organic matter, appropriate for most lawn and garden uses.
Often, a preconceived notion when purchasing topsoil is: the darker, the better. While an increase in darkness is often associated with an increase in organic matter, soils which are very dark or grayish may have been dredged from swampy areas. These soils are usually very finely textured, acidic, lacking in nutrients, and best avoided.
As with any purchase, find out about the product before bringing it home. Unlike an article of clothing, a pile of topsoil is not easily returned! For more information on purchasing topsoil or soil testing, or other home and garden information, contact the UConn Home and Garden Education Center, toll-free, at 860-486-6271, visit the website www.ladybug.uconn.edu, or contact your local Cooperative Extension Office.