Root Flare Exposure and Pruning of Girdling Roots
A healthy tree begins with a proper planting depth and continues with maintaining a root flare that is above the soil line. The root flare area (also called the crown or root collar) is that area where the main stem tissue transitions to root tissue. The bark on the main stem is corky while the “bark” on the roots is smooth and waxy. The transition zone (root flare) needs to be dry and free of soil, mulch, and vines.
As you look around town at well formed and healthy trees, invariably you will discover that the root flare is exposed. There are always exceptions to the rule. However, research has shown that trees that have their root flare area uncovered are under much less stress and are much more able to withstand the onslaught of stress factors that may come against it.
Girdling roots are often associated with a root flare that is too deep in the soil. Small roots form that cross over the larger buttress roots and cause a restriction that can eventually kill a tree. Pruning the girdling roots relieves this stress and allows a tree to live to full maturity. Girdling roots often start in the nursery, especially in container grown trees. The effects of the girdling roots may not become evident for many years after planting. Live Oaks, Pistachios, Cedar Elms, and Magnolias are particularly prone to developing girdling roots, but most tree species can develop them.
Before and after pictures of a Cedar Elm with serious girdling roots. The tree has grown to a good size but was beginning to show signs of decline in the upper crown. The root structure was contricted and could no longer support the size that the tree had grown to. This tree will recover and live many more years as a mature, beautiful shade tree.
These trees have all been planted too deeply and are suffering from this poor cultural practice. Improper tree planting depth is a problem in the industry and even professionals often plant them too deep. The thinking goes that the roots need to be down in the soil to survive the heat and drought. A healthy tree will grow roots where it needs them to mine the soil for moisture and nutrients, but a covered root flare is always a recipe for a short lived and unhealthy tree.
Tree Shepherds can assess your trees and expose the root flares if necessary. When the root flares are exposed, girdling roots can be pruned.