A good example is a container-grown plant, where the roots are often forced to grow in a circular fashion. If these trees are not pruned at the time of transplanting, this growth pattern can cause girdling roots. Figure 1 Figure 2 Figure 3 Root pruning is a absolute must for any container-grown tree or shrub at the time of transplanting. Three to five slashes are made vertically down the rootball and about an inch into the rootball. One or two slashes into the bottom of the rootball are made at a depth of three to four inches.
Some people go further by fraying out the pruned roots.
For plants susceptible to root girdling, an inspection should be made when the tree is approximately six inches in diameter. A positive diagnosis can only be made by exposing the roots. Soil is carefully removed to a depth of at least 12 inches, with care taken to prevent serious mechanical injury to the roots. If girdling roots are found on a plant with known susceptibility, the girdling root must be removed, a process normally carried out with a chisel. Removing a girdling root is a wound in its own right.