Topsoil and Subsoil

The subsoil lies below the topsoil. The structure of the subsoil has an important effect on the condition of the soil as a whole.

A clay subsoil underneath a loose porous topsoil prevents too much water from draining out of the soil. This means that moisture is retained, which helps plants remain healthy.

A subsoil of sand or gravel assists drainage from a clay loam topsoil. This prevents excess water from clogging the topsoil.

However if there is sandy soil topsoil on open gravel subsoil, something needs to be done to make the soil more compact.

If heavy loam lies on top of clay, drainage needs to be improved.