Cindy Schwie – Ramsey County Master Gardener
My heart sank as I sat in one of my first Master Gardener courses and the professor spoke to the group about stem-girdling tree roots. I knew right away that the Norway maple that was planted on my boulevard 10 years ago was buried too deep because the "root flare" was not visible. My Norway’s trunk looked more like a utility pole, straight up and down and not like the leg on a pair of sailor’s pants. There it was the middle of January, as I started counting the weeks until I could get out in my yard and start clearing away the soil to try and save my Norway!
What are stem-girdling roots? In a nutshell (no pun intended) when a tree is planted too deep, the roots seek out oxygen. Years ago I was told that the tree that you see above ground is a mirror of the root growth, below ground. This is not the least bit true. In reality ninety percent of all tree roots grow in the top 12" of soil because oxygen exists there, unless of course there are cracks in the ground, which then makes it possible for oxygen to be present farther down.
When a tree is planted too deep, it goes into a survival mode whereby the roots start growing upward searching for oxygen. When they reach the oxygen layer they start growing laterally. Left alone, this sparks the beginning of the end for the tree because as the roots grow and the tree diameter increases in size, the girdling roots begin to compress the trunk and eventually water and nutrients are cut-off.
As you can see in the picture below, the dark horizontal line on the trunk was one of the girdled roots that was choking the life out of my tree.
There are several symptoms of a tree that has stem-girdling roots, but be advised that the symptoms can also be indications of other problems with a tree. Some signs that your tree might have stem-girdling roots are that it is leaning to one side; it has unexplained twig or branch dieback, and leaves turn brown. Again, keep in mind that these symptoms can also be caused by other problems and that the only real way to diagnose your tree for stem-girdling roots is to examine it. This doesn’t mean that you need to call a professional forester; a homeowner can also do the inspection.
First, start by removing the sod and soil around the base of the tree. Next, proceed to carefully scoop out the soil to expose the tree roots. The deeper your tree has been planted the longer it will take you to reach the root flare. As you dig, look for any roots that are pinching off the trunk. A suspect root can be clipped. The soil that you remove should not be put back in around the roots, simply mulch the exposed roots with wood chips.
Brochure for a comprehensive guide to stem-girdling roots
Otherwise, you can purchase a copy of the brochure by calling the University of Minnesota Extension Service at (612) 624-4900 and request a "A Practitioner's Guide to Stem Girdling Roots of Trees," by Professor Gary Johnson.
About this time you might be asking yourself how my tree has done in the three years since I went searching for "killer" roots to snip. I’m happy to
report that it still graces my boulevard. Have I extended the life of my tree? I don’t know just yet. The tree was planted over 12" too deep and had been growing that way for so long that damage has definitely been done. However, one thing I can say for sure is that I’m glad that I gave it my best shot.
University of Minnesota Extension Service
Containerized Tree Planting Guidelines
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Remove the tree from the container by holding the trunk of the tree with one hand and pushing down on the container with the other hand. If the container does not come off easily cut it down two sides.
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The tree may be planted too deep in the pot. Remove the soil down to the first roots. This is where the tree starts to flare out.
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If there are encircling roots, slice through them with a sharp knife. Make 3 – 4 vertical cuts in the root ball. After cutting, pull the roots apart.
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Dig the hole just deep enough so the first roots will be just below finished grade. Do not loosen soil under the root ball below this depth.
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Planting site should be prepared 3-5 times the width of the soil ball.
