Root Pruning

Trees can slowly weaken and die over a period of years or decades because of root girdling. Roots begin to grow around the main stem of the tree and cut off or restrict the movement of water, plant nutrients and stored food reserves. This is largely due to a number of inappropriate planting practices.

Possible Indications of Stem Girdling Roots:

Over time, growth of the branches on the side of the plant affected by the girdling will be slowed. As injury progresses, leaves will become smaller and lighter green, fewer leaves will be produced, and eventually the branch will begin to die back. Death of the entire plant can occur in five to 20 years; watering, fertilizing and pruning will do little to correct the problem.

Certain trees are more prone to this problem than others. Lindens, magnolias, pines, and maples are susceptible to root girdling. On the other hand, oaks, ash, and elm are known for their ability to form functional root grafts and are rarely adversely affected by girdling roots.

Normal trees have a gentle trunk flair or buttress at their base. (Fig. 4) Trunks that grow straight up from the ground as though they were a telephone pole (Fig. 1) can be suspected of having girdling roots (Fig. 2). Trunks with a straight side or a concave depression on one side may also have a girdling root.

Development of girdling roots is not well understood but is normally thought to be the result of unfavorable conditions which prevent roots from growing out in a normal

Restricted root space–such as tree pits in urban areas–also may result in girdling roots. There is some suggestion, too, that constant mulching, a practice that builds “volcano” piles around trees, may cause the formation of girdling roots.

For trees susceptible to root girdling, an inspection should be made when the tree is approximately six inches in diameter. A positive diagnosis can only be made by exposing the roots. Soil is carefully removed with an air excavation tool to a depth of at least 12 inches, with care taken to prevent mechanical injury to the roots. If girdling roots are found on a plant with known susceptibility, the girdling root must be removed, a process normally carried out with a hand chisel.

Telephone Pole Tree

Figure 1

Telephone pole tree, the root flair of this tree is buried beneath the soil line. Soil against the trunk of the tree encourages circling roots and rot of the trunk. This tree should have the soil removed down to the base of the root flair.

Girdling Roots

Figure 2

Girdling roots around the base of this tree will get tighter as the tree and roots grow, eventually strangling the tree. These roots need exposed, as seen in the picture, and carefully removed to allow the tree room to grow

"Volcano Mulch"

Figure 3

This “volcano” mulch pile around this tree is a inviting environment for epicormic roots to sprout from the trunk of the tree and grow in circles around the tree. Soil and mulch against the trunk also creates an environment for decay in the base of the tree. Mulch and soil need to be removed from trunk and root flair area to improve health.

Healthy Root Flair

Figure 4

Healthy, well tapered, root flair at the base of the tree. A flat mulch ring around the tree protects it from mower damage and competing grass and weeds.