This is something usually carried out upon a mature tree in when the customer is happy with the size and shape of the tree but feels that the canopy is in need of thinning. This involves a climber cutting and removing secondary, crossing and dead or dangerous branches from inside the tree. This allows the wind to pass through the crown and a reduces the risk of branch failure. It also allows for a greater amount of light to pass through the canopy which is what many clients are looking for.
Crown thinning can be carried out at anytime of year. It is preferable to avoid early spring, just before budding and during flowering, or in early autumn, before the leaves fall, especially if it is a relatively heavy crown thin.
Crown thinning on a tree is different from Crown reduction in the the height of the tree is usually kept the same but branches are removed to thin the tree. This has the benefit of better health for the tree, less risk of disease and allows more light through tree into a garden or property.