Issue: February 26, 2005

Protecting Tree Roots

Question:

I have a flagstone walkway that runs from the entrance of my house to the street. About midway along this flagstone walkway, it is extremely close to a tree whose roots have lifted a number of the flagstones, making the pathway quite uneven.

I'm trying to relocate some of the flagstones from a straight line to cause the path to curve around the tree at a greater distance in an effort to skirt the problem area.

Do you have any suggestions as to how I can deal with this situation to avoid damaging the tree while evening out the walkway?

- M. Wachs

Answer:

You are doing the right thing to move the walkway farther from the trunk of the tree. By making a large arc, you move away from the large surface roots that are causing your problems. Such a curving walkway can be very attractive and, if there is room to move far enough from the tree, the problem may not reoccur for many years. However, if you are limited in the space you have to move the sidewalk, you can try bridging the problem.

By bridging the problem, I mean that you can literally build a bridge over the problem area, or you can create tunnels from chimney flue tiles to protect the roots. In either case, you must be careful not to damage the roots as you are building protection for the roots.

If you wish to build a small "moon bridge" (such as is often seen in Japanese gardens) you can construct one, being careful not to damage roots as you put posts in the ground to support the bridge. This may be appropriate for your landscape. If it is not appropriate, you can use chimney flue tiles that have been cut to remove one of the sides. These tiles can then be placed on the ground over the roots to create a tunnel, allowing root enlargement under the tile and traffic over the surface of the tile. The edges of the tile that are in contact with the ground should be supported so that they donāt dig into the ground causing the tile to sink. If this tile over the roots is too tall, you can use sand or pea gravel to create a base on which to place the flagstones. This will raise the flagstones to the level of the top of the tile. Gradually increase the thickness of the gravel base so that the pathway grade is not too steep for safe and easy walking. You may apply the gravel only in the area of the pathway or as mulch in a large area around the tree.

If you choose to use the tunnel method and apply pea gravel mulch around the tree, keep the gravel from the very base of the tree to protect the "crown" of the tree. If you apply gravel mulch to a large area, it can provide a useful base for a sitting area with lawn furniture or as a foundation upon which you can place flower pots. This will create a container flower garden in the shade near the area in which you have created the tunnel. While this flower garden is not necessary, it may be helpful in directing traffic to remain on the flagstones and away from the roots that may be damaged by foot traffic. Problems such as yours offer opportunities for creative changes in the landscape. Enjoy the possibilities.

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Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.