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Forestry Extension Urban Forestry

Tree with stem-girdling root
Stem girdling root (A) encircles the tree when the soil line (B) is more than 1-2 inches over the tree roots. Tell-tale above ground signs of possible SGRs include slow-healing wounds (C) and stem sprouts (D).

Stem-Girdling Roots:
Serious Threat to Landscape Trees

Do you have planted landscape trees that exhibit any, or some combination, of the following symptoms:

  • Slow-growing
  • Late leaf-out
  • Early leaf drop
  • Burnt leaf margins
  • Tree trunk goes straight into the ground like a utility pole
  • Trunk wounds do not heal quickly
  • Sucker-sprouts growing from the base of the tree
  • Sudden breakage at ground-line during a high wind

More often than not, most (if not all) of these symptoms are due to stem-girdling roots.

Stem-girdling roots, or SGRs, are the result of roots encircling the tree stem and eventually strangling the stem tissue. Water and nutrients cannot travel up the trunk, depriving the leaves of the building blocks required for photosynthesis. What little food the leaves do produce cannot travel down the stem to the roots, preventing vital water and nutrient absorption.

While SGRs are not necessarily new, (the first cases were reported back in 1937) the phenomenon seems to have become more prevalent during the past 15 to 20 years. Some arborists point to the widespread use of the hydraulic tree spade and the push to get trees out of the nursery and into the landscape.

As a tree makes its way from the nursery pot, to the liner nursery, and finally to the landscape, there is an opportunity for planting a little deeper in the ground. The result is the trunk of an improperly planted tree resembles a telephone pole instead of the trunk's normal flaring observed in trees growing in the wild.

By planting a tree too deep, or heaping mounds of mulch around a young tree, an environment is created for roots to grow abnormally and develop into SGRs. If there is more than 1 inch of soil over the flare/branch root area, you are asking for trouble.

An easy way to check for proper depth is to take a knitting needle and probe downward through the soil around the circumference of the trunk. You are looking for the large roots that are running for the large roots that are running away from the stem. Once you hit such a root, mark the spot on the needle with your finger and remove it from the soil. If the depth is greater than 1 inch, the tree is too deep.

A large tree that has been in the ground for several years with a well-developed SGR is a lost cause and should be removed. For smaller and more recently planted trees, remove the excess soil from around the trunk to expose the root flare. If you find an SGR, cut the root with a hand pruner.

If you just brought a tree home from the nursery and are waiting to plant it, remove the top of the root ball until you expose the root flare. You might be surprised how much excess soil you have bought. Should you find an SGR, the best advice is to return it to the nursery, point out the problem and ask for a replacement. You might also want to check out the replacement before you head for home.

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