The root of tree health

Landscape trees provide a multitude of environmental and aesthetic benefits. When most people think of trees, they picture the canopy. Yet, the visible portion of a tree can only be as healthy as the root system supporting it.

Roots are the foundation of a tree. They anchor it in the soil and absorb the water and nutrients needed for survival. The root system of a mature tree can extend three times or more beyond the diameter of the canopy. Contrary to popular belief, most tree roots are located within the top 12-15 inches of soil, particularly in the heavy clay soils common to areas north of Georgia’s Fall Line.

Unfortunately, several common landscaping practices can damage tree roots and contribute to tree decline.

Compacted soil

Roots need to breathe! When soil particles become compressed, the pore spaces between them are reduced, limiting the roots’ ability to absorb air and water.

Soil compaction is one of the greatest threats to tree health and often goes unnoticed. It can result from lawn maintenance equipment, parking vehicles beneath trees or even repeated foot traffic. Compaction is especially severe when these activities occur on wet clay soil. As with many tree problems, prevention is the best solution.

Surface roots in turf areas

Soil compaction can also encourage shallow root growth. Tree roots naturally get thicker each year — just like tree trunks — and eventually break the soil surface. Soil erosion can also expose roots, and certain species, such as maples are particularly prone to developing surface roots.

Exposed roots can create tripping hazards and difficulties with mowing turfgrass. Homeowners often ask whether these roots can be cut. The answer is no. Cutting roots can compromise the tree’s stability, while damage from lawn mowers can create entry points for diseases and insects. Covering exposed roots with soil is not recommended either, as it can suffocate them.

The best remedy for exposed tree roots is to cover them with pine bark, aged wood chips or other organic materials. Creating mulch islands around groups of trees can provide additional protection while reducing maintenance challenges.

Mulch “Volcanoes”

Proper mulching benefits trees, but one common practice can do more harm than good. Piling mulch into a deep cone around the trunk, described as a “mulch volcano,” can lead to gradual tree decline.

Mulch should never be placed directly against the trunk because it can:

— Trap moisture against the bark, encouraging decay and disease. 

— Bury the tree’s root flare where the trunk widens and transitions to the root system. It helps to provide stability and allows for proper oxygen exchange for the roots. The root flare should always remain visible. (The trunk should never look like a telephone pole emerging from the ground.)

— Encourage adventitious roots to form from the trunk rather than the root system. These roots can eventually girdle the tree and restrict the movement of water and nutrients. 

— Create habitat for insects and rodents that may damage the trunk. 

In the case of mulch, the old adage of “if a little is good, a lot is better” does not apply. A 3-inch layer of organic mulch applied in a ring (think “donut”) across the root zone is beneficial. It helps to retain moisture, moderate soil temperatures in all seasons, suppress weeds and protect from mechanical damage.

Healthy roots are the key to healthy trees. By protecting the root system and avoiding common landscaping mistakes, homeowners can enjoy stronger, longer-lived trees and the many benefits they bring to the landscape.

Kathy Hensley works for the University of Georgia Cooperative Extension Service in Bibb County. The county office provides resources for gardeners as well as educational services and community support. Visit their office at 715 Oglethorpe Street, call them at 748-310-5350 or email their staff at bibb.extension@uga.edu.