Finding the right soil is crucial to the health, functionality, and look of your garden. At its most basic level, topsoil is the top layer of soil, and contains the nutrients that all plants need to grow and survive. Though the specific blends of topsoil vary depending the plants they are nourishing, just about every topsoil layer is 5 to 12 inches deep, with a calculated mixture of clay, silt and sand to provide plants with the proper growing and nutrient-receiving facilities.