Fill dirt is typically sourced from the subsoil that sits at least six inches below the surface, under the topsoil. It does not contain any organic or biological components that will eventually decompose, which means it packs well, and is unlikely to shift and settle over time. After the dirt has been collected, it is sifted multiple times to remove rocks and debris. This is why it’s also called clean fill.
Although it lacks the nutrients vital to plant growth, it is usually used to fill holes, level out surfaces or build up hills where plants will not be grown, due to its availability and affordability. Use it in projects where shape retention over time is important but keep in mind that it will retain moisture unlike fill sand.
If you need help deciding which fill material to use, please refer to our article on the difference between fill sand & fill dirt.