Topsoil is the upper layer of soil, typically the top 2-3 inches, which contains the highest concentration of organic matter and nutrients. Topsoil support simpler plant life such as grasses, bedding plants and other foliage with shallow root systems. Filler dirt is used to fill a hole or depression and to build-up an area. Fill dirt can provide a lasting solution to level an area whereas filling an area with organic matter (leaves, logs, etc.) will not.