Topsoil refers to the rich and fertile topmost layer of earth that is composed from years of the chemical and physical actions of a particular climate on rock and organic material in the soil. This gradual decomposition creates a soil texture that is best for plant growth. However, topsoil is not only scarce, but also often expensive. Topsoil may be put directly on grass for improved grass health.
When topsoil, or any other organic material, is added to already growing grass, the process is referred to as topdressing. The recommended amount is approximately ½ inch or less of topsoil over the lawn. Using topsoil on grass helps to reinvigorate grass growth as the soil is enriched with a balanced level of nutrients. Make sure the topsoil is dry and free of lumps so it will reach the grass roots easily. Water well after spreading the topsoil. A cubic yard of topsoil is enough to topdress 650 square feet of lawn at a depth of ½ inch.
Topsoil is a rare and hard to find commodity, and the material that is sold as topsoil is usually a mixture of sand, sawdust, manure, biosolids and subsoils. This soil is commonly referred to a three-way or five-way mixes, and is not only fertile but also has good drainage, with its loose and open structure. The three-way or five-way mixes produce the same results as topsoil, and the only instance where results are unsatisfactory is when the material is not incorporated properly with the soil or grass.
In areas where topsoil is unavailable or very expensive, compost is the best alternative, recommends Pete Landschoot of the Penn State University Extension. Compost is an easy to obtain and inexpensive source of organic material that is not only good as a soil amendment prior to the establishment of a lawn but also as a topdressing material for use over existing grass. Compost helps to relieve compaction in clay soils and increases the water- and nutrient-retaining capacity of lighter, sandy soils.
Preparing for Topdressing
In order to make sure that the use of topsoil serves its purpose, it is best to prepare the lawn prior to application. The recommended time to topdress grass is during the spring or fall. Dethatch and aerate the lawn before topdressing, as this breaks up soil compaction and helps the topsoil mix in well with the soil. Adding topsoil on top of compacted, thatched grass only creates layers that do not reach the grass roots, doing more harm than good. Aerate the grass with a rented power core cultivator or a hand- and foot-operated cultivating tool.
- Washington State University Extension; 3-Way & 5-Way Soil Mixes; Steve Witcher, et al.; 1996
- "Taylor's Master Guide to Landscaping"; Rita Buchanan; 2000
- "Turfgrass Maintenance Reduction Handbook"; Doug Brede; 2000
- "Safe and Easy Lawn Care"; Barbara Ellis; 1997