Before placing a bare root tree or containerized plant in the ground, be sure to check for girdling roots.
Girdling roots work very much the way your grandmother’s elastic undergarment did, in that they cut off circulation and restrict movement. Girdling roots can kill your tree.
What is girdling?
To ‘girdle’ means to surround something, to go around its girth. When girdling happens aboveground, it refers to the removal of a ring of bark. This bark contains the cambium layer, which houses the vascular bundles that transport water, oxygen, and nutrients. It often occurs when tree supports are left on for too long or installed improperly. Girdling roots create the same problem by encircling the trunk and neighboring roots, effectively cutting off the supply of water, oxygen, and nutrients. Wherever girdling occurs, whatever lies beyond the girdle will, in most cases, die.
In a normal, healthy tree, perennial roots reach out horizontally, anchoring the tree in place and providing a pathway for water, oxygen, and nutrients to enter the body of the tree. Those important elements move through the xylem of transport roots, after being collected by feeder roots. Unless they can’t.
Sometimes, containerized plants become root bound. If you take the plant out of its pot, roots can be seen circling around, looking for a way out. As these roots get bigger in diameter, they slow or halt the transport of life-giving water, oxygen, and nutrients, effectively choking itself to death. This often starts with improper planting depth.
Roots emerge from the body of the tree just below the root collar, or where the trunk flares out. [If you plant a tree and it looks like a pencil sticking out of the ground, it is planted too deeply.] If the root collar is buried, as often occurs with modern, mass-produced trees, they become predisposed to girdling roots, as well as pest infestations and fungal diseases. This also places the roots deeper in the soil, where it is harder for them to access the water, nutrients, and oxygen they need.
Symptoms of girdling roots
In some cases, girdling roots can be seen simply by looking at the base of the trunk. If the problem is occurring underground, you may still be able to identify the problem when these symptoms are seen:
In severe cases, the bole indentation can create structurally weak areas that are prone to twisting or breaking. Of course, these symptoms are not always seen. In many cases, a tree will struggle on, growing but not thriving. Within 2 to 10 years, the tree dies for no apparent reason.
How to prevent girdling roots
When you plant a tree or shrub, start by inspecting the root system. Loosen and straighten any circling roots. Roots that have been circling for more than two years will be too woody to straighten and should be removed.
Next, make sure that the planting hole is the proper depth and diameter. Do not “spin” roots into a too small hole. Dig the hole wide enough to allow the roots to spread out horizontally. While wider is better, deeper is not. Dig the planting hole only as deep as is needed for the roots to be just below the soil surface. Planting it any deeper than that is setting the stage for failure.
When planting in compacted soil, it is important to loosen the surrounding soil, or the new roots will simply circle around in this new 'container'. Other obstructions, such as building foundations or large rocks can also caused girdling roots. Mulching the area with arborist wood chips is an excellent way to (slowly) reduce compaction while keeping down weeds, stabilizing soil temperatures, and retaining moisture.
Responding to girdling roots
Giving a tree with girdling roots more water and fertilizer will not fix the problem.
Girdling roots must be removed if a tree is to survive. These roots should first be exposed by removing the surrounding soil. Then, 6 to 12 inches from the trunk, the girdling roots must be cut away, usually with a chisel or a saw. This first cut is to prevent damage to the trunk, in case there is any tension being placed on the root. [An apple tree with a 20” diameter trunk can weigh nearly 2-1/2 tons, so tension is definitely occurring somewhere!] The final cut is made where the root meets the trunk. If it is possible to remove the girdling root(s) without disturbing the surrounding roots, do so. Otherwise, leave it where it is and it will, eventually, decompose.
Especially large girdling roots must be removed in stages by a professional arborist. To cut it off abruptly would eliminate the supply of too much water and nutrients to the tree, putting the entire tree at risk.
Tree roots provide the life blood of the tree. If those roots start circling, corrective measures must be taken for the tree to survive
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