Bulk topsoil is sold at garden centers by the “yard.” This unit is a cubic yard, measuring 36 inches on all sides. The recommended depth of additional topsoil for creating a new lawn on poor existing soil is three to six inches of soil.
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Topsoil varies in quality based upon its source. Healthy topsoil will have a balanced amount of organic material already mixed into the soil. Inspect the soil carefully for its appearance, texture and odor. Have the contractor show evidence that the topsoil meets the American Society of Landscape Architects specifications for landscape projects.
Topsoil should look dark with a deep, rich brown to blackish color. The soil should crumble in your hand after you add a little water and squeeze it into a ball. If it stays compacted, there may be too much clay in the soil, and if it falls apart immediately, there may be too much sand. Topsoil should have a sweet odor like a forest floor in the autumn. If it is sour smelling, then it probably came from too far underground to be topsoil.
The weight of topsoil changes with its moisture level, but the average weight for a yard is approximately 2,250 lbs.
Adding three inches of topsoil to a 100-square-foot area would require one yard of topsoil, or enough to fill about a standard pickup truck bed.