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Delbert Johnson Doctor of Stumpology Girdling Roots: A Problem of Shade Trees Trees can slowly weaken and die over a period of several years by the strangling or girdling action of roots. Some tree roots that begin to grow around or along the main trunk and large lateral roots can cut off or restrict the movement of moisture and plant nutrients into the SYMPTOMS: Over a period of time, branches on the sides of the tree affected by the girdling root will slowdown in growth. Injury may eventually show up as weakened top growth, short terminal twigs, and smaller, lighter green leaves. The branches will eventually become weakened by strangulation and the tree may die over a period of 5 to 15 years. Good cultural practices of fertilization, watering, and pruning will not offset the slow death by girdling roots. Figure 1. Normal tree trunk Normal trees have a flare or buttress root swelling at the base of with flare or buttress at soil the trunk as shown in Figure 1. Tree trunks without flare that grow line. straight up from the ground as if a soil fill has been placed around the tree can be suspected of having girdling roots as illustrated in Figure 2. Trunks of trees with a flat side or concave depression at the ground surface instead of a swelling may also have a girdling root as seen in Figure 3. Positive diagnosis of girdling roots below ground can be made by carefully digging away the soil around the base of the tree to expose Figure 2. Girdling root. the encircling roots. Trunk may grow straight up. CA USE: The development of girdling roots on trees is usually the result of unfavorable conditions which prevent the roots from growing in a normal spreading manner. For example, the roots of container-grown plants will grow out to the sides and then spiral and coil around the side and bottom of the container. If the trees are grown in the container too long, they become root-bound. In transplanting container-grown trees or shrubs that are root-bound, 3 or 4 slits should be made down the sides of the root ball with a knife or pruning shear, and then the roots should be spread out by hand. If the encircling roots are not cut and straightened out, they will Figure 3. Girdling root caused by obstruction such eventually girdle, or strangle, the stem of the plant. as curb, sidewalk, wall or SOLUTION: Positive diagnosis of girdling roots is important since compacted soil. other factors can cause the same symptoms. Girdling roots can be found growing from the soil surface to a depth of a couple feet. The exposed girdling root often can be cut from the trunk or lateral root at the point of attachment with a chisel and mallet. Several inches of the girdling root should be removed to prevent it from growing back together. If there are many girdling roots, the removal process should be gradual, perhaps taking two to three years. This allows new roots to develop and replace those that had been supporting the tree with water and nutrients. After the girdling roots are removed, weakened trees may respond with improved growth if careful pruning, watering, and fertilizer applications are used.