When do you use fill dirt or topsoil?

Answer

Use fill dirt to increase the grade or to fill a deep area. Use topsoil for the plant layer.

For structural work, use the material that the project specification identifies.

Fill dirt and topsoil selection

Material	Primary use	Important limit
Fill dirt	Grade change and deep fill	Use specified fill for structural work
Topsoil	Grass and other plant areas	Do not use as structural fill
Garden soil mix	Raised beds and gardens	Get the mixture data from the supplier

Fill dirt

Fill dirt usually has a small quantity of organic material. It can include subsoil, sand, stones, and clay.

Use it below the plant layer when you must increase the grade. Compact it as specified in the project specification.

Topsoil supplies the plant layer. It can contain organic material and biological activity that help plant growth.

Use topsoil for a lawn, a garden, or a plant bed. Ask the supplier for the soil mixture and test data.

A deep lawn repair can use fill dirt below the surface. Put the specified topsoil depth above the fill dirt.

A garden soil mix can be necessary for a raised bed. Do not think that all topsoil has the necessary mixture.

Specified fill and density tests can be necessary for a retaining wall, road, or structural pad.

Obey the project specification and local requirements. NC State Extension gives information about construction compaction and plant soil.