What is structural soil?
A. Structural soil refers to a group of soil mixes that are designed to be both load bearing AND to support tree growth. Because they are load bearing, they can be used under pavement, including streets. They typically function by using large gravel or similar material that form a lattice work that provides the support needed to hold up pavement. A good topsoil is mixed in and fills the voids between the gravel, providing uncompacted growing space, moisture and nutrients for roots. Structural soils can greatly increase rooting area for urban trees. Although many municipalities plant trees directly in structural soils, they can be confined to the underpavement areas with ordinary soils used in the open “tree pit” areas.
