Potting Soil

• The most common use for potting soil is in container gardens. Potting soil is typically a combination of sterilized compost, peat moss, aggregates and fertilizers. The product is usually pasteurized to destroy microbes in the soil that could harm a plant in the confines of a container as well as seeds, diseases and other potential problems that compost may bring to the soil. By contrast, beneficial microbes are usually present in topsoil.
  
  

Topsoil Uses

• Topsoil that is sold in garden centers is different from topsoil found in nature. Natural topsoil is any soil present in the surface layer of the ground. The topsoil layer of the earth is typically rich in decaying organic material and weathered rock particles. Because this resource is not plentiful in some areas, manufactured topsoil mixes may be created for home landscaping projects such as construction of soil berms, mounds or garden beds.
  
  

Topsoil Mixes

• Manufactured topsoil is made of a combination of subsoil, sand, manure, biosolids and sawdust. Depending on the quantity of mixtures and components, the topsoil may be called three-way mixes or five-way mixes. There is no legal standard for topsoil mixes, so the components and mixture may vary based on manufacturer preference and availability of materials. Topsoil mixes must be fast draining yet retain moisture so that plants will not be susceptible to drought stress. Unlike potting soil, topsoil mixes are not pasteurized. The topsoil mixes that contain biosolids may contain low levels of pathogens or heavy metals.
  
  

Using Topsoil

• Topsoil mixes must be incorporated into already existing topsoil in order to create a transition zone for the two soils to work well. This will allow water to pass between the two soils easily. Topsoil that is not worked into the native zone will become more waterlogged in rainy weather and drier in warm weather. Topsoil mixes may also contain higher levels of salts, which can prevent seeds from sprouting or cause plants to wither and die.