Incorrect planting can lead to the production of girdling roots below the soil grade. Girdling roots are lateral roots that emerge at or slightly below the soil surface and cut into at least one side of the main trunk. A girdled trunk/stem will weaken a tree, and significantly reduce its lifespan because of a predisposition to diseases, insects and wind throw. Girdling roots can form when root collars are buried, or when a tree from a nursery is planted with pot-bound, circling roots. A pot-bound root will continue to circle the trunk, eventually resulting in a girdling root as the root grows in diameter.
Several research trials have shown that breaking up pot-bound root balls before planting reduces girdling root formation without reducing the health of the plant if watered and mulched appropriately post planting. Roots take the path of least resistance in growth. If planting holes are not dug wide enough and if the soil is compacted and clayey, such physical properties will simulate a container and encourage circling roots. One way to prevent the formation of circling roots is to dig the planting hole twice as wide as the root ball; this will encourage roots to grow out radially.
Unlike biotic problems (e.g., insect pests and diseases), abiotic problems that result from poor horticultural practices can almost always be avoided with proper planning and preparation—so don’t get caught with girdling roots. If you see girdling roots, they should be removed carefully with a chisel or a saw. If there are multiple large girdling roots on a tree, removal of these roots in several stages is recommended, because these roots can still be providing water and nutrients to the tree.
While girdling roots are preventable, they are still common in the landscape and should be removed whenever possible to improve the health and structure of the tree.