What is a Stem Girdling Root? (SGR)
What is happening below the surface of the soil is something few people think about, but there is an abundance of life and activity belowground! Fine root-tips gently elongate to search for resources like water and nutrients. Insects decompose organic matter and tunnel through the soil. Fungus breaks down wood and other material.
Many of these processes do not readily impact people or give us much reason to be concerned.
But in the general scope of tree care, there are a number of reasons to be aware and possibly concerned about what is going on below ground.
This article will discuss what a Stem Girdling Root (SGR) is, how they develop, what they can do, and what can be done if a tree has one.
An SGR is a root that has wrapped around the trunk or other major anchoring roots. It's that simple. While they can be benign in adolescence, as time and growth increases the effect can become serious to the support and longevity of a tree.
If left alone, some SGRs can eventually choke the lower trunk and reduce or eliminate the tree's ability to move water and nutrients through the living cambium. The inside of a tree has a vascular system, kind of like a bunch of straws. As the tree grows, these straws remain on the exterior of the new wood. A root that is encircling the tree will be pushed against as the trunk is swelling. The end result is that the straws get more and more compressed, to the point where they are stopped, like kinking a garden hose.
This can lead to major dieback in the upper canopy, and a tree that is more likely to fall over during a storm.
Anchorage is a major component of what roots do. A root that twists around will not be supportive.
Now that we have covered what an SGR is and how they are harmful, let's go into how they develop.
Most trees that have major girdling roots came from a nursery!
They develop circling roots when they are small and in a pot. You may have heard the term “root-bound” before. It describes a plant that has been in a pot for too long and its roots have wrapped and twisted within the pot searching and exploiting every available resource.
For a small shrub or perennial flower it is less of a big deal. For a tree that has the capacity to live for a long time it is a big deal. If those roots are not cut or pulled apart at the time of planting, then there is a good chance they will develop into SGRs and significantly reduce the lifespan.
Occasionally SGRs happen in nature. It is usually the result of a root hitting a hard object, like a rock or foundation, thus being turned. They may not be as significant but the only way to be certain of the extent is to do what's called a root crown excavation. This is the process of gently removing soil from the base of a tree to uncover what lies beneath.
Now while root pruning seems like a bad idea, if caught early enough it is the best practice. Just like in pruning the canopy of a tree, there are some basics that should be followed to reduce problems if root pruning is done such as making clean cuts, avoiding additional damage, and making as small as cuts as possible.
If you notice a wrapping or twisting root around the base of your shade or ornamental trees, consider consulting with an arborist to determine if action needs to be taken.
