Girdling Roots: To Cut or Not to Cut

Last fall, a client called me to look at her sycamore tree and advise her of whether it was likely to survive. The tree was about 25 years old, otherwise healthy, and contributed greatly to her landscape. However, a girdling root was wrapping around the base of the tree trunk, and it was beginning to flatten one side of the trunk with constriction.

A girdling root is a root that grows to encircle a tree trunk, usually at ground level or below the soil line. Initially, girdling roots can be easy to ignore since they are small and not posing an immediate threat to tree health and structure. Over the long term, however, they pose a problem. As we hesitate to prune a girdling root, sometimes for years, the root starts to constrict part or all of the tree trunk tighter and tighter. As a girdling root grows, it gradually chokes the sap flow from delivering food through the trunk phloem to the roots below. This strangling root not only starves at least a portion of the root system, it disrupts the tree structure and weakens the trunk. As the choker root slowly depletes the root system of energy to absorb water and elements, it may also kill parts of the tree crown linked to and depending on the depleted roots. Eventually, the trunk may break where the girdling root binds it. 

When you discover the problem, now is always the time to address the situation. If the root is less than 2 inches in diameter, take the courage to go ahead and carefully cut the girdling root. It will only grow to become a larger issue later. If the root is over 2 inches in diameter, it is a good idea to consult with a Certified Arborist to see if it is still possible to safely cut the girdling root. A larger girdling root may have become structurally important for the tree. An arborist will have the expertise to determine if and where a larger root can be cut. In the case of the sycamore, the root was 3 inches in diameter. The client was wise to consult with me and I used my expertise as an arborist to determine the girdling root could be cut.

The operation of cutting a girdling root can be labor-intensive and tedious, depending on the size and location of the root. The offending root may be embedded in the tree, and it may be half-buried in the soil. If the cut location is buried at all in soil, you will need to remove the soil that surrounds the cut location to make a cleaner cut and avoid extra wear or damage to your saw or pruners. Select the smallest tool you can practically use to avoid unintentionally injuring your plant. For the sycamore, I used a pruning hand saw to cut this root after removing all the soil I could from the work area.

Hidden in the soil, many mysteries remained. After spending 30 minutes cutting the girdling root, I found it was lying on top of another root of similar size. I presumed the lower root was not girdling. By this time, I was exhausted, and I hoped not to have wounded the root below with my saw work. I did take time to replace the soil and mulch I had taken from around the root.

The owner and I will monitor this tree. Part of the tree crown may have benefitted greatly from the troubling root, and some dieback may result from my cutting it. The owner and I will do any follow-up pruning needed to remove failing branches in the crown as they occur. Overall, this tree will provide a much longer service to the owner by our action today.

If you would like to learn more about managing girdling roots, see the article Girdling Roots from the University of Maryland Extension.