By John Stonaker, Sep 24 2019 05:25PM
As a tree grows, so does its root system. In fact, for many trees the entire root system grows wider than the tree’s branches. Therefore, if a tree is placed near a hard surface such as a driveway, parking lot, or sidewalk, roots may eventually buckle the surface, creating an unsightly and potentially dangerous condition. There are ways, however, to make your trees compatible with paved surfaces, retaining and enhancing the value of your residential or commercial property.
When it comes to tree placement and care, prevention is always the best medicine. If you have not yet planted your trees, now is the time to plan properly in order to avoid future problems. First, consider planting trees that do not have shallow root systems. Shallow-rooted trees include a variety of maple, tulip, ash, sweetgum, pin oak, poplar, and willow trees, among others. A tree specialist can direct you to trees that do well in your area and that tend to have deep root systems.
Allow sufficient distance from your surface to your tree at maturity. If your tree will be up to 30 feet when full grown, allow 3-4 feet from paving. If 50 feet, allow 5-6 feet. If more, allow at least 8 feet from paved surfaces. This should limit damage or heaving of surfaces from the largest tree roots and allow the roots to dive down deeply for water.
Consider installing a root barrier along the sidewalk or driveway. The barrier can be made of plastic or geotextile, should be at least 2 feet deep, and extend 5-6 feet in both directions along the surface.
If your planting is very new and roots have not extended far from the initial root ball or haven’t reached the paved surface, you can try installing a root barrier. For more established plantings, consider modifying the paved surface using one or more of the following methods, but be sure to check with your tree specialist first to determine what the best course of action is for your situation:
• Replace concrete with asphalt, which is more flexible and not as likely to crack
• Lay down a geogrid mesh on top of the roots to force them downward
• Lay a barrier of several inches of coarse gravel, forcing the roots to grow downward
• Pour a thicker layer of concrete or asphalt (6 inches), making it more difficult for roots to push through
• Curve the surface or make it more narrow to allow the tree roots more room to expand
Several of these methods can be combined, such as the geogrid mesh, gravel, and asphalt, with the help of a knowledgeable tree expert and paving service.
You can amend the tree itself, but some changes risk damaging the tree. A well-pruned tree can help keep root growth under control, so consider a heavy crown pruning to slow the tree’s growth. Done by a professional, this is actually the healthiest option.
Excavate under the roots with an air excavation tool to remove the dirt. Then either leave the space open or fill it with pea gravel. This will give the roots room to move downward when layers of paving are placed on top.
Cutting the roots should be a last resort, because the roots are the tree’s lifeline. More mature trees, unhealthy trees, and certain species are less tolerant of root pruning. Larger roots of 3” diameter or more will be susceptible to disease or insect damage, weakening the entire tree.
If you must prune roots, have an expert do it, and use a stump grinder, if possible, to shave the tops of the roots rather than cutting them. The roots being pruned should be no closer than three times the diameter of the tree. For example, a tree with a 12” diameter should not have its roots cut closer than 3 feet away. Cut even farther for trees judged to be intolerant of root pruning.
Contact a tree expert before you do any tree modifications or surface repairs. If you’re in the Central New Jersey area, contact us here at Stonaker to see how we can help you save your tree and improve the value and function of your residential or commercial property.