Girdling roots, a serious problem for many trees in our urban forest, are roots that encircle the trunk and/or root flare of a tree. These roots stunt the growth of your tree and are detrimental to the long term health of your tree. As a result of girdling roots, a tree may display symptoms such as crown thinning, discolored leaves, branch dieback, premature leaf drop and stunted growth.
Girdling roots can be more prevalent with specific tree species, but they can occur on all trees. A leading factor that will increase the risk of girdling roots developing is by not exposing the root flare at the time of planting. The root flare is the bottom portion of the trunk, sometimes called the trunk flare, that is to be slightly above grade when the tree is planted. This allows the roots below the root flare to grow down and away from the trunk rather than up and across. When a tree is planted too deep, the buried roots have limited access to oxygen and water, causing them to grow upwards and potentially encircling (girdling) the trunk. The deeper the roots are buried; the fewer roots can establish themselves effectively.
A second factor that can encourage girdling roots is excessive mulch around the trunk of the tree. This buildup of mulch around the trunk of the tree can be an environment for roots to grow, which will result in roots encircling the trunk of the tree. Mulch should always be level with the grade of the ground, 3” depth max and kept a minimum of 6” away from the root flare of the tree. When you reapply mulch, make sure to try and best remove any excess mulch from prior years.
Additional factors that can encourage girdling roots includes poor soils, high in clay. These types of soils can be difficult for roots to penetrate, resulting in them following the path of least resistance and potentially encircling the root flare. Root collar excavations, soil amendments and vertical mulching can be prescriptions for your tree to help in soil environments such as described above.
To identify girdling roots, inspect the trunk and excavate around the root flare to check for roots circling the trunk. This type of excavation is called a root collar excavation. Once identified, it’s crucial to act and remove girdling roots as best as possible. Girdling roots not removed can reduce water and nutrient flow, making trees more vulnerable to diseases, pests, and environmental stress. Following the excavation, fresh topsoil mixed with leaf mulch or compost can help to improve the soil environment and structure.
Exposing the root flare and having it at or slightly above grade at the time of planting, avoiding excessive mulch, and maintaining healthy soil can help prevent girdling roots. Trees like maples, lindens, beeches, pines, oaks, poplars, and elms are particularly susceptible, especially if they are container-grown.
If you suspect your tree has girdling roots, consult a certified arborist for diagnosis and treatment. Early intervention can help save your tree. Remember, healthy trees are vital to a thriving ecosystem, so don’t let girdling roots become a silent threat to your landscape.
