There’s often some confusion with clients as to what a tree pit is. A common misconception is that a tree pit is a volume where the roots will be (or is intended to be) confined.
A tree pit is the initial hole a tree is planted in – and should NOT be the area in which tree roots are confined. The roots should be allowed to leave the tree pit to obtain the water and nutrients they require as they grow.
Wrapping the sides of a tree pit in root barriers or concrete is a death sentence for the trees in most cases and should be avoided at all costs.
See photo 1 for an example of how root barriers should NOT be used to restrict outward root growth. To protect the adjacent hard surface, root barriers should only have been installed along the edge of the hard surface instead of completely surrounding the tree.
Larger tree specimens, with larger root balls or containers, will require a larger tree pit for the tree installation. Semi-mature tree specimens can have root balls with diameters exceeding 1m, so careful consideration needs to be taken especially when installing trees adjacent to hard landscape, see photo 2.
In cases where trees are to be planted within hard landscape, consideration should be made for the installation of root cells beneath adjacent hard paving to allow tree roots to have more available rooting volume adjacent to the tree pit, whilst minimising root damage to hard surfaces.
For further information on minimising tree failures by considering factors such as rooting volume requirements, soil compaction and protecting hard services, refer to our 5-part blog on Specifying Trees in Residential Schemes.