Avoiding Girdling Roots and Planting Problems
Marianne C. Ophardt
Washington State University Extension
Area Horticulture Specialist
How long will my tree live? If it's in a protected place on a college campus, it may live 40 to 80 years. If it's located in a city park, with luck it will survive 25 to 30 years; and if it’s growing in a suburban street right-of-way, it might last 12 to 18 years. In cities, trees last only about 3 to 4 years. Why? Experts indicate that it's usually not insects or disease that ravage these trees... it's most often related to problems with the tree roots or the soil.
The same holds true for the sick or unthrifty trees. The problem is usually not an insect or disease, it's most often related to a problem with the roots... improper planting techniques; girdling or encircling roots; poor soil conditions; and watering difficulties. Many young trees die before they ever develop a good root system.
Let's talk a little about roots. Roots are alive. They need oxygen for respiration and normal plant metabolism. It's easy to forget the importance of roots to a tree. They enable a tree to take up water and nutrients in the soil. Roots store carbohydrates and synthesize organic compounds involved in regulating plant growth. For a tree to be healthy, the roots must be healthy. According to Dr. Rita L. Hummel, Washington State University Horticulturist, "The importance of healthy roots and a favorable root environment cannot be overstated."
If so many tree problems involve roots and problems with root systems, where do these problems originate? Some are due to faulty root systems that developed in the nursery where the trees were first propagated. It is there that roots develop kinks or sharp bends. This is due to the handling of the seedling in the nursery. With mass production and mechanization of the nursery industry, seedlings may be jammed into pots that don't have adequate room for their root system. In other cases, the seedlings are left too long in smaller pots before they are planted into larger pots. When planted into the larger pots, the roots continue to grow in a circle and never fill out into the larger root area.
"Once formed, kinks, circles, and girdles in woody root systems have three possible fates: 1) the root dies; 2) the kinked or circled portion of the roots is pruned out at transplanting; or 3) the root lives... and grows in circumference until at some point the root girdles itself, the stem, or another main root. This can restrict the flow of water and nutrients in the plant and compromise the ability of the tree to support itself," says Hummel. It may take many years for the root problem to become apparent, evidenced only by the gradual decline of a tree or a tree may fail to grow well from the time of planting.
To diagnose a tree problem as a "root or soil problem," the owner must check the root system. It's easy to check the leaves or trunk of a tree for a problem, but how do you check the roots? You can look for girdling roots by inspecting the tree where it enters the ground. In some cases you'll be able to see roots that are twisted around the trunk and are girdling or "choking" the tree. However, girdling roots can also be under the surface of the soil. A clue that the girdling root is a problem will be a lack of the normal flare to the trunk on one side of the tree.
If you suspect that there are girdling roots below the soil, you'll need to carefully excavate around the trunk. You can do this by gently removing the soil from around the tree base until you find the main roots. A watering can or hose can be used to help clean the roots for your scrutiny. If the main roots radiate out from the trunk unimpeded by other roots, girdling roots are not the problem. Girdling or encircling roots restrict the growth of the trunk and roots. If girdling roots are found, a trained arborist can help you decide what action to take. In some cases the offending root can be cut, solving the problem. In other cases, the problem may require removal of the entire tree for safety.
Younger trees that fail to thrive and grow after a year or two, should be checked to see if the roots have grown out of the original root ball. This should also be done very carefully, trying not to sever roots. Check is the depth of planting. The top of the root ball of a mulched tree should be just below the soil surface. Anything deeper than an inch or two is too deep. In this situation, the roots can't get air and will gradually die... and the tree will die too.
When you dig down to check the root depth, don't look for the fine feeder roots proliferating at the top of the root ball and assume that everything's satisfactory. In some cases, this is the only place where roots have grown, because it's the only place that they could get some air. You should find the main woody roots radiating out from the trunk just below the soil surface. Ifthese main roots are deeper, you should replant the tree at the proper depth. Do this in early spring before new growth begins or in the fall after the leaves drop.
Another "root" problem that may also be revealed in a root ball excavation... is the failure to loosen and cut encircling roots of container grown trees at planting time. Locally, we've seen trees and shrubs that have been in the ground for five years or more which seem to do fairly well and then gradually die. Upon removal, their owners have found that the root ball kept circling in the same pattern of the original pot and the roots never moved out of the root ball. In fact, the root system even fit back in the original pot several years or more after planting!
Yet another "root" problem that shows up when tree root balls are excavated... is the failure of trees roots to grow beyond the original root ball with balled and burlapped trees. While landscape contractors' standards often specify leaving the bottom portion of burlap around a root ball, there are problems with this practice. In many cases the burlap fails to rot and roots don't grow beyond the burlap, even three years after planting. To avoid this problem, remove the burlap once the tree is situated in the planting hole at the correct depth. Cut the burlap away from the root ball, moving of the root ball as little as possible.
Finally the old adage of "hindsight is better than foresight" doesn't necessarily hold true when considering girdling tree roots and related root problems. Most of these problems are better avoided in advance by checking trees for kinked and girdling roots before planting and then following proper planting procedures. In this case, hindsight is just too late to save many of the trees. Pay attention to the roots before you plant and help your trees live longer!