United Mulch and Soil Top soil is an all-natural product coming straight from nature. Top soil is a 3/8 minus mixture of screened bark, peat moss and native soils. Top soil is commonly used as an amendment to give added nutrients to soil and is used as a main ingredient in container mixes, greenhouse mixes, potting soils, box gardens and any other general soil preparation. Top soil can also be used as a top dressing for any landscaping needs as well as any land reclamation projects.