Plant Answers

Tree Decline and Sidewalk Trees

Questions always arise concerning the decline in health and vigor of shade trees. Although many tree problems can be directly attributed to insects, diseases, or weather conditions such as drought or heat, the problem of tree decline usually lies below the ground in some form of root stress.

Often, this hidden stress exists for years, and it does not become apparent until symptoms manifest themselves in the above-ground portion of the tree that concern sets in. Some of the symptoms that are signs of trouble are leaves curling and dying and bare branches. Other signs are smaller than normal foliage, with varying shades of red, yellow and green. Soil compaction is probably the number one cause of root stress. It is essential that air can enter through the soil so that oxygen can be absorbed by the roots and carbon dioxide, when given off, can readily move up from the root zone and escape into the atmosphere. Where soil compaction exists, this process cannot occur normally and the result is the death of many roots.

Other causes of root stress are poor soil drainage, surfacing materials, (i.e. concrete or black top), below?ground service/utility lines, septic system chemicals, or any alteration of the soil levels (either the addition or removal of soil).

Girdling roots are another very real cause of shade tree decline. If trees are improperly planted or located in areas where normal root development isn't possible, their roots may eventually grow around the base of the tree, either just above or below the soil surface, and gradually strangle the tree to death. If you are unable to see any girdling roots and see no evidence of normal outward flaring of the trunk as it goes into the ground, beware! Carefully dig just below the surface (2 to 4 inches) and you will probably find one or more roots growing around the trunk or other primary roots. If girdling roots are involved, cut the troublesome root or roots with a sharp chisel. If this is not the problem, try to improve whatever the condition is that is causing the stress.

Although each cause of a tree's root stress must be dealt with differently, it would be helpful to reduce the plant's demand on the root system by carefully pruning back the top of the tree and removing any unwanted branches. Never remove more than 25% of the total canopy.

The ultimate stressed?out plant has to be a sidewalk tree. Too much or not enough water, poor and compacted soil, cramped roots, abuse from passing dogs-its no wonder that sidewalk plants rarely live for more than a few years.

The odds are against a sidewalk tree from the start. To begin with, it's usually planted in a hole that is too small. Five feet by three feet is the absolute minimum. All of the water and oxygen that is going to reach the tree's root system has to enter through that little opening in the concrete.

In the summer, when the tree is assaulted by heat bouncing off nearby sidewalks, streets and buildings, it can easily lose more water through its leaves than it can readily replace through its roots. Drought stress, heat scorch and a general weakening of the tree can result, leaving it more vulnerable to insect attack, diseases and other problems.

Too much water is as big a problem as too little. Drainage is likely to be poor because of compacted soil. Water that gets into the root zone may be slow to move out. Most trees do not thrive if their roots are constantly surrounded by water. Studies in the Midwest and New York City indicate that this is their number one cause of death.

Insufficient room to grow is another frequent problem with sidewalk trees. Crews digging planting holes for trees often run into old foundations, roadbeds, and building debris. Unless this is removed and new soil brought in, the tree's roots won't have much chance, and if the roots don't grow, the tree won't grow. A tree must grow or it will die. Of course, if someone could pull each one out and root prune annually and give each one lots of daily nutrients and water like a bonsai, a sidewalk tree could live a long time without growing.

Sidewalk trees can do a lot to make a walk along a city street more pleasant, but because they are located beside busy traffic areas, they are exposed to a lot of incidental abuse. Regular visits by passing dogs can kill a tree in a very short period of time. Vandalism, too, can destroy trees. A reasonable life expectancy for a sidewalk tree is 10 to 15 years.

Regardless of whether you are concerned about a sidewalk tree or just the tree growing in your lawn, plants do experience stress during periods of environmental "hard times". In the case of sidewalk trees, the "hard times" may last a lifetime.