What does “girdling” roots mean, and what are the consequences?
In general, a trunk or limb is girdled when something is tightly wrapped around it. This can be a piece of twine or wire, for example, or an actual root from the plant itself. Girdling roots choke off the flow of water and nutrients from the roots to the leaves, as well as preventing food produced in the leaves from reaching the roots.
They can also compress and weaken the trunk of a tree at or above the root collar flare (the junction between the trunk and the main roots), causing it to lean and lose its stability. Trees having girdling roots suffer a slow decline in health and a premature death.
A girdling root will also affect the appearance of the tree trunk. Usually tree trunks flare out where they enter the ground. The root will prevent the collar flare, and sometimes the trunk may get narrower and appear flattened or sunken.
Most tree roots are in the top 6 to 24 inches of soil and grow out from the trunk in a spreading manner. Cultural practices that can adversely affect this natural root pattern, and possibly cause girdling roots, include: 1) Planting in a hole that is too small so the roots cannot easily spread out, 2) planting container-grown trees that have roots growing in a circular pattern, 3) planting a bare root tree by twisting roots to fit into a small hole, and 4) leaving wire baskets, burlap and any part of a container in the planting hole.
The most common theory of the cause of girdling roots is that they develop as a result of trees being planted too deeply. When root systems are buried, less oxygen and water is available. The roots will grow up towards the surface of the soil and tend to encircle the trunk. The more deeply buried the roots are, the fewer the roots available for the tree to become established.
Symptoms of girdling roots include: 1) Leaf scorch, early fall color, early leaf drop, or damage on one or two branches, 2) abnormally small leaf size, 3) excessive twig dieback, or the appearance of large, dead, leafless branches, 4) thin appearance to the crown, or overall stunting, 5) little or no trunk taper at the collar, 6) leaning, and 7) susceptibility to environmental extremes and other problems.
The only sure way to determine if a girdling root is the cause of a problem is to examine the root system and its relationship to the tree trunk. Look for roots, ropes or wires encircling the trunk. If the trunk is abnormally flat on one side at the soil line, carefully dig below the soil line to look for a girdling root. Look for wires or ropes that were not removed at transplanting time, but which now may be girdling the trunk.