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Land (and Roots) Down Under

November 23, 2005

I have a new appreciation for the value of proper tree planting. My home is about 25 years old, and most of the trees are of that vintage as well. We have been seeing some dieback and decline in our trees and needed the help of an arborist to prune, to help us with a pH/nutrient stress problem with the river birch, and to remove a redbud that has succumbed to cankers, wood rot, and decay. As we began looking more closely at my trees, it was obvious that many did not have much of a flare at the base. My arborist did a collar excavation of two crabapples, a river birch, a red oak, and three small pines. We were trying to determine how much time, labor, and money to put into these trees.

Observing the aboveground portion of the trees, we saw either no flare of the trunk, partial flare, or one flat side on the trunk. The collar excavation revealed that, belowground, many of the roots were growing around the trunk and had become girdling roots. All of these trees had been planted too deeply, with the trunk flare at its greatest width 6 to 8 inches or more below the soil line.

How could the trees grow well for the past 25 years with deep planting and girdling roots? Does this mean deep planting and girdling roots are really not a problem? Actually, I stated that these trees have been showing some decline and dieback, but nothing major, other than the redbud. That species is notorious for having winter injury and canker problems. I have been watching the top of my red oak for the last 2 years, as it develops scorching each August. I have been concerned about possible oak wilt, bacterial leaf scorch, or drought stress. In fact, the tree tested negative for oak wilt and bacterial leaf scorch. That tree had the worst girdling roots of any of my trees, and symptoms were worst on that tree. The river birch also has had extensive dieback. I thought this was because of our high-pH soils and nutrient stress. It also had a severe problem with deep planting and some girdling roots. As my arborist pointed out, the girdling roots on these trees are only now beginning to really cut off water and nutrient movement in the tree. It has taken 25 years of slow growth under conditions of deep planting and fair soil conditions for girdling roots to begin to show their effect.

The collars of these trees will remain exposed. That area of the trunk needs to be exposed to air. We are also taking some chances and removing some of the girdling roots. We have debated about how many and which ones to remove because we do not want to kill the trees. On the other hand, if some are not removed, the tree will surely die anyway.

There is no quick cure for these problems. The major point of this article is that proper planting depth and root spread are critical to the long-term life of the tree. Insist on a good job. By the time you start to see problems, it may be too late to save the tree; you will have to start over with a smaller tree; and the person who planted it is probably long gone. Your local Extension office has information and fact sheets on proper planting of trees and shrubs.

My job is to diagnose plant problems. Often I see only a few dying branches or scorched leaves and receive limited information with which to make a diagnosis. Often diseases such as Verticillium wilt, oak wilt, or bacterial leaf scorch are blamed by those in the field without laboratory confirmation. Labs such as the Plant Clinic at the University of Illinois can help get to the true cause of the problem. Now, when I see a tree with branch decline, scorch, or other aboveground problems that have me stumped, I will be asking for much more information on the belowground conditions on the site.

Author: Nancy Pataky


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