Root barrier to protect patio

I am planning to plant a tree in my small yard and remembered that you once wrote about a way to keep tree roots from damaging the patio. What is the method to protect the patio without damaging the tree?

There are several methods to avoid the problem. Each method prevents roots from growing under the patio and protects the paving material.

The first method is to dig a trench along the edge of the patio each year. As you dig, you will cut the roots and prevent them from becoming large enough to damage the paving material of your patio. If the tree is a very vigorous tree that grows rapidly, this root pruning should be done twice a year.

A barrier may be placed into the soil to prevent the extension of roots under the patio. This barrier may be a solid substance (metal, plastic, or concrete). This will require digging a trench one time and placing the barrier material vertically into the trench to block the growth of roots. Perhaps the easiest and cheapest material to use for this is a thick plastic material that may be purchased in sheets. However, with this or other material, the overlap between sheets of material becomes the weak point in the barrier. Often the roots will find their way past the barrier, and in time these roots may cause the damage you wish to prevent.

Finally, there is a combination physical and chemical barrier that may be installed at the edge of the patio (root barrier or biobarrier). This material is a thin plastic fabric containing small dots of hard plastic. These plastic dots are impregnated with an herbicide which will not kill the tree but will stop growth of roots as they approach the barrier. This chemical is usually trifluralin herbicide. This herbicide is not absorbed into the plant and translocated; therefore, it does not kill the rest of the plant. It has only low solubility in water and doesn't wash away to other places. This means it will stay in the region of the root barrier and not interfere with the growth of roots elsewhere. This method of root control will involve the least effort (trench one time) and should give many years of protection to the patio.

Since you are planning to create a root barrier at the time you plant the new tree, you will not harm the tree when installing the root barrier. However, if any of the root control measures mentioned is used near established trees, care must be taken not to dig trenches too near the tree. Digging too closely to the tree can result in damage to major roots. This will result in damage or death of the tree. When trenching near established trees, maintain sufficient distance. The root barrier will also be effective in protecting pavement from established trees if the trees are not injured during the installation process.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question