THE ROOT OF THE PROBLEM
by Scott Diffenderfer – Board Certified Master Arborist
In landscape trees, abnormal root systems often develop through planting or cultural practices. For this reason, care in planting and plant choice is important to assure successful tree growth. Planting practices such as deep planting, narrow planting holes, deep mulching (referred to as volcano mulching), and confined planting locations such as small planters will cause abnormal root development. In addition, nursery production methods such as the use of containers that induce encircling roots, propagation that encourages stem origin adventitious roots, or tillage practices such as “hilling-up” plowing to control weeds will cause improper root development.
An inspection completed by Mead Tree & Turf Care of a declining little leaf linden in Montgomery County revealed several girdling and crossover roots. The pictures below show before and after views of this tree. Note the 2 red arrows on the second picture, indicating one root and illustrating the circular path this root follows. This root and several others are girdling the trunk of the tree. As the trunk and root diameters increase with annual growth, the constriction will increase, and further contribute to the decline of the tree. The original depth of the mulch was only 2 to 3 inches, but the soil was mounded over the root ball and this allowed the roots to infiltrate the mounded area.
NORMAL VS ABNORMAL ROOT SYSTEMS
Normal root systems typically have main laterals that radiate from all sides of the stem/root interface, with root spread commonly about three times the branch spread. Many tree species also produce diagonal roots, which grow at a sharp angle into the soil and stabilize trees. Sinker roots grow downward from lateral roots, and function in support and absorption. From main-order laterals arise woody and non-woody roots, which magnify the absorption of water and nutrients. These roots proliferate in zones of favorable moisture and nutrition.
The picture here shows a typical and normally developed root system of a linden tree. When compared to the girdling roots in the previous picture, it is easy to see how the abnormal root system can compromise the health of a tree, affecting the flow of water and nutrients to the tree.
Care in choosing and planting landscape trees will prevent abnormal root systems from developing. In addition to checking the root system before planting, avoiding common mistakes such as planting too deep or deep (volcano) mulching can prevent a healthy tree from developing problems.
Once a tree is compromised, a root collar examination using air excavation process is a preferred choice. Our arborists at Mead Tree & Turf Care find this method is the most efficient and causes very little damage to tree roots.
This picture shows a typical air excavation application. The air gun is attached to an air compressor and supplies a steady stream of compressed air for excavation. After excavating the root zone, roots that are wrapped around the tree trunk are carefully removed. Approximately 1- foot from the root crown, the area is backfilled with organic material and lightly mulched. It is desirable to have the final grade of the mulched area just 2 to 3 inches above the grade of the turf when applicable.