Garden Tips: Roots could be strangling your tree

When a homeowner comes to me with a sample of a sick tree, I look for signs and symptoms. Signs are the actual culprit causing the problem, such as aphids or a whitish coating on leaves from powdery mildew fungus. Signs make diagnosis easier and more definitive.

Symptoms tell you something is wrong, but not what is wrong. Symptoms include wilting, distorted growth and dieback. I have to rely on symptoms to determine the most likely cause of a problem.

I also gather information about how the tree was planted, its care and descriptive details of the problem. Often I cannot provide just one cause because there may be cultural factors involved. I suggest the most likely possibilities, and the owner must go home and try to determine the actual cause and then remedy the situation.

Root problems is a nebulous term I often render as a diagnosis. Many tree problems are related to the roots, the soil and watering practices. A common root problem is a stem girdling root (SGR). SGRs have been a problem for tree owners ever since the nursery industry began growing trees in containers instead of in the ground.

The SGRs start when the roots reach the sides of pots or containers and then begin circling the container. This creates roots that encircle the main stem, either partially or sometimes entirely. If not corrected at planting time, these roots will continue to grow in the same pattern. As trees get bigger, their roots grow in length and girth.

Eventually, a SGR will start choking off the flow of water and nutrients from the roots. Depending on how quickly the tree grows and how severe the strangling, SGRs can lead to a tree's demise within several years of planting or -- 10 years or more in the future.

As a result of SGRs, a tree will exhibit symptoms that indicate something is wrong. These can include crispy brown leaf edges (leaf scorch), stunted growth, yellowing leaves, leaf drop and gradual dieback of branches and entire limbs. However, these same symptoms might be caused by other problems, such as chronic drought stress, physical damage to the trunk or roots, and compacted soil.

To determine if the problem is being caused by SGRs, owners must do some of their own detective work. While some SGRs are visible at the base of a tree's trunk, others are not. Detection requires looking for clues and possibly doing some excavation.

Tree trunks usually flare out at the base, some species more than others. A clue that one or more SGRs is involved is a lack of flare or even an indentation at the base of the trunk. If this is noted but no SGR is visible, the soil in that area should be carefully excavated using a trowel and not-too-strong jet of water. Many, but not all, SGRs will be found in the top several inches of soil.

If a sizable SGR is found on a large tree, I recommend hiring a certified arborist to assess the situation. They will excavate the SGR and use a sharp chisel or saw to cut the root where it attaches to the trunk. If the SGR is deeply embedded in trunk tissue, they will leave it in place after severing. If removal will not damage the plant, they may remove it.

-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.

This story was originally published August 7, 2014 at 12:00 AM with the headline "Garden Tips: Roots could be strangling your tree."