Ask An Arborist: December 10, 2009

Cutting Tree Roots

Images Submitted by Reader (sorry for the grainy appearance)

Susan from Peachtree City Writes...

"Our river birch tree is only 44" away from the driveway and 64" away from the sidewalk. We have already had to repair the sidewalk due to root damage...[Can we] cut the tree roots down 6 feet or so at the sidewalk and driveway to keep from damaging the concrete?"

The Answer Is...

Well, the first part of my answer is hoping that other readers will learn from your mistake of choosing a bad location for a tree. When choosing a location, you must consider the tree's mature size not only above but below the ground. Root systems of mature trees can extend to and upwards of 50% or more beyond the reach of the tree's branches (canopy). If a mature tree is going to have a canopy that is 50 feet wide (25 feet in all directions from the trunk), that is the minimum amount of root space it should have free of structures such as driveways, sidewalks, etc. The foundations of buildings may be less susceptible because they usually extend deeper than the root system and many tree roots as they grow will "bend" around such obstacles.

Compounding the problem of planting the tree too closely to the sidewalk and driveway is the fact that river birch trees are notorious for having large surface roots. The same shallow root habit is common amongst maples, cherries and ornamental pears. Trying to cover the shallow roots with soil is not only bad for the tree but is somewhat futile as the tree will simply continue to grow in this manner.

Now back to your original question of cutting the roots to prevent further damage. Tree roots serve several functions including the transporting of nutrients from the soil and providing the structural stability that keeps the tree upright. Cutting all the roots on two sides at distances of 4-6 feet from the trunk will not only sever the roots responsible for nutrient uptake, but will also seriously destabilize the tree. Think of it as cutting the legs off a table. If you remove two legs, the table will fall over. I would not suggest even cutting just one side simply because you are too close to the tree.

Fans of the Neal Boortz show may remember that back in 2004, his executive producer and right-hand person, Belinda Skelton experienced a similar situation that was caused by a careless utility worker. You can read about that outcome here (scroll towards the bottom).

Your options are, in my opinion, remove the tree, live with the idea of repeated sidewalk/driveway repairs or re-engineer the driveway and sidewalk. I have seen people remove sections of their driveway and replace it with gravel in order to relieve the conflict between the roots and the driveway. I have seen sidewalks elevated or removed for the same purposes, but this would require county and/or city approval. Measures such as these are usually reserved for older specimens or trees of significance as shown below:

If you are concerned about the trees in your landscape, you can contact a Certified Arborist or a professional tree company in your area through the web site of the Georgia Arborist Association.

If you have comments or questions about this article or want to submit a question that may be used in a future article, please email me.

Unless otherwise noted, Images & Drawings Copyrighted © 2009 by Theresa Schrum - All rights reserved