December 17, 2021 - Stem Girdling Root of Trees
Tree-related questions are quite common at the Extension Brown County Horticulture Help Desk, and many issues concern trees that were planted by the homeowner about 15 – 25 years ago. These trees were perfectly healthy for many years but then started to slowly decline as they age. Typical symptoms are a thinning of the tree’s canopy, smaller and off-colored leaves, dying branches, early fall colors, early leaf drop, deep cracks in the trunk, etc. The most common trees involved are maples and lindens, but ash, honey locust, ornamental pears, and Japanese tree lilacs are other trees we see affected. While there might be several factors causing the issues including insects and diseases, the most common reason is that the tree was planted too deeply, to begin with!
Trees that are planted too deeply (as little as 1” – 2” in some cases) often develop what is called a stem girdling root(s). These roots that encircle the trunk rather than grow away from the tree’s base eventually restrict the flow of water and nutrients, resulting in a steady decline of the tree. These offending roots can be visible at the soil surface, but also can be several inches below the ground. When the tree is young these roots do not cause a problem but as the tree ages, the trunk grows into these encircling roots, slowly strangling the tree as well as making it more susceptible to attack by insects and diseases. In advanced cases, the tree trunk becomes structurally unsound and can snap off at the base!
To make this girdled root diagnosis, we ask that the homeowner e-mail pictures of the affected tree, particularly of the lower trunk as it enters the ground. This allows for an evaluation of the presence of what are called root flares. A properly planted tree will show root shoulders flaring away from the trunk above the level of the ground. If the trunk shows no flaring and is straight up and down like a telephone pole, chances are it has a stem girdling root condition. The earlier you identify this problem, the more likely you will be able to treat the issue. Treatment would typically involve excavating around the base of the tree to locate the offending root and then chiseling out that root. It may be best to employ the services of a certified arborist who will have the equipment and expertise to treat the tree, if not too late. You can find a certified arborist in your area by searching the International Society of Arboriculture at isa-arbor.com.
The best way to address stem girdling root is to plant your tree properly, to begin with. There are several important techniques involved in planting a tree correctly, but a critical step is to locate the root collar and then plant the tree with the collar 1”-2” above the ground level. In some balled and burlapped trees (often referred to simply as B & B) the root collar maybe 6”-8” or more below what appears to be the soil level in the B & B! If the collar is not exposed and planted correctly, the tree is likely to develop a girdled root in the future. This is so frustrating for the homeowner who has enjoyed the tree for many years, only to see it decline when it could have been prevented when it was put in the ground.
For more information on stem girdling root and planting a tree properly, check out the two resources below:
UW- Madison Division of Extension brochure “Proper Tree Planting Techniques (B&B)” by our former Horticulture Educator, Vijai Pandian.
“A Practitioner’s Guide to Stem Girdling Roots of Trees,” University of Minnesota Extension Service, 2000.
As always, feel free to contact the Horticulture Help Desk for any questions related to your home landscape. The Help Desk can be contacted by calling 920-391-4615 or emailing firstname.lastname@example.org. Written by: Doug Hartman, Extension Brown County Horticulture Assistant