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Tree Roots - How Do They Grow?

In my last blog, I looked at tree conflicts that are above ground. In this blog, I will examine the root system of trees and some of the challenges they often face.

A few months ago, I was walking in the woods with my daughter, and we saw a huge tree that was uprooted with the roots fully exposed. According to her, the root system of the tree was not what she imagined it to be. The root system was wide and appeared to be growing horizontally instead of vertically. She wanted to know the reason for this form of growth.

According to Douglas L. Airhart, Ph.D., Professor of Horticulture, Certified Arborist and Guy Zimmerman III, Area Forester, Tennessee Division of Forestry in their article “Tree Roots Myths” the reason that roots grow horizontally instead of vertically is “ root systems generally grow as flat pancakes rather than lollipops.”

Contrary to popular belief, tree roots tend to spread or grow outwards rather than simply grow downwards into the soil. Hence, the pancake and lollipop analogy.

As important as the roots are to a tree, it is easily overlooked in comparison to the portion of the tree that is above the ground. Roots provide an anchorage for the tree. Additionally, roots are important because they perform the functions of absorption, conduction, and storage. The root of a tree will grow wherever it finds space, supply of oxygen, sufficient moisture, and adequate soil texture.

Tree roots are often misunderstood because of some of the myths that exist regarding tree roots. Airhart and Zimmerman listed three of the existing myths to be:

  • “The roots of trees extend as far as the canopy or dripline”: We know that the roots extend far beyond the dripline, frequently, two or three times further.

  • “Trees have a tap root that grows deep into the soil, so they are protected from damage”: Roots stay close to the surface of the soil (especially in clay soils) to get the oxygen that it needs to survive.

  • “Tree roots are tough, so they do not need protection:” This is far from the truth as the woody tough parts of the roots are closest to the tree trunk and the smaller more vulnerable roots are further outwards.

Due to these myths, the roots of trees are often neglected; therefore, roots are subjected to loss and destruction, especially during construction and other urban activities. When trees are damaged above ground, the tree compartmentalizes and seals its wounds. This does not occur when roots are damaged. Thus, tree roots must be protected to ensure the health and longevity of trees.

For more information on how to care for trees, visit our Cuyahoga ReLeaf page.

Blog Author: Colleen Berg, Education Program Specialist

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