3946. Girdling roots

 A tree is girdled when something is tightly wrapped around the trunk or stem. A stem girdling root circles or partially circles the base of a tree at or just below the soil surface.

Stem girdling roots choke off the flow of water and nutrients between the roots and branches and 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. Girdling roots may girdle other roots, but there is no known harm in this. Trees having stem girdling roots suffer a slow decline in health and a premature death.

The appearance of a tree trunk will be affected by a girdling root. Usually tree trunks flare out where they enter the ground. The root will prevent the collar flare, sometimes the trunk may get narrower and appear flattened or sunken. The threat depends on the size of the root and the amount of the tree’s circumference affected. It is almost impossible to predict if a developing girdling root will cause problems for a tree. However, if a tree has girdling roots it is more likely to have problems than one without them.

The causal factors may be genetic or cultural. At the end of this article is a list of trees that may be more prone to stem girdling roots. Cultural practices that may cause girdling include poor growing practices or poor planting techniques.

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 include: (1) Planting in a hole that is too small so the roots can not 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. (4) Leaving wire baskets, burlap and any part of a container in the planting hole. (5) Piling mulch against the trunk of a tree (creating a mulch volcano).

The most common theory of the cause of stem 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 and Diagnosis

Symptoms of stem girdling roots include: (1) Scorch, early fall color, early leaf drop, damage on one or two branches. (2) Abnormally small leaf size. (3) Excessive twig dieback, the appearance of large, dead, leafless branches (stagheading). (4) Thin appearance to the crown, overall stunting. (5) Little or no trunk taper at the collar. (6) Leaning (7) Susceptibility to environmental extremes and other biotic problems.

Many of these symptoms can also be characteristic of other causes, such as drought or nutrient imbalances. A plant disease diagnostic laboratory cannot identify this problem. The only sure way to determine if a stem girdling root is the cause of a problem is to examine the root system and its relationship to the tree trunk.

Integrated Pest Management Strategies:

1. Inspection. Carefully inspect the root system at the time of planting. Remove any girdling root on bare-root plants. Cut away the wrapping on balled & burlapped plants, check for girdling roots and natural root flare. Cut through any circling roots of container grown plants in a few places.

On mature trees, if any of the symptoms appear, examine the root collar by probing into the soil near the trunk flare with a stiff wire to find the depth of any stem girdling roots.

2. Planting. Dig planting holes 2 to 3 times as wide as the root ball, with sloped sides and no deeper than the root ball. In heavy clay soil dig the holes shallower than the root ball by at least 3 inches. Make sure there is no soil above the root flare. If there is soil above the flare, very carefully remove it down to the flare. Apply mulch no deeper than 3 inches and never against the trunk of the tree.

3. Ongoing care. Make sure to water a newly planted tree regularly and water any tree during drought periods. Avoid using fast–release fertilizers, they may burn tree roots. Reduce environmental stresses on established trees and add nutrients if it appears there is a deficiency. Periodically examine the root flare to make sure it appears normal. If stem girdling roots are present, gently remove the soil until you can find the root collar flare. This may need to be done by a certified arborist.

4. Pruning. Stem girdling roots are commonly removed by using wood gouges, saws or pruners if they have caused minimal stem compression. If one has caused extensive compression, removal treatment must be careful not to damage the stem. Such roots are frequently left in place when they cannot be removed safely. Again, it may be necessary to consult with a certified arborist.

5. Removal. If stem compression from a stem girldling root is more than one third to one half of the stem circumference, removal of that tree should be considered because the tree’s stability is compromised.