Trees are hardy plants, and their roots fight back against man-made limits around them. In urban and suburban landscapes, tree roots are often forced to grow between buildings or under driveways and walkways—and they can cause costly damage if left unchecked.
“Before you plant a new tree in your yard, you need to understand how a tree could damage your property, and take appropriate measures to prevent that damage,” says Tchukki Andersen, a board-certified Master Arborist and staff arborist with the Tree Care Industry Association (TCIA).
Woody tree roots thicken as they grow, gradually pushing shallow roots toward the surface. Since soil near the surface is best suited for root growth, most tree roots are just below the surface, placing them directly in conflict with man-made obstacles. Where the soil is covered by a solid driveway or patio, upward growing roots will grow against the underside of the pavement or pavers.
“Most damage is found six feet or less from the tree, since roots become smaller and less damaging the further they are from the trunk,” says Andersen. “Keep this in mind before you plant. That small sapling could become a large shade tree with roots spreading 30 or 40 feet outward from the trunk.”
Some homeowners, masons and landscapers manage intrusive roots by grinding down or removing them. This can be expensive, and is harmful to the tree. Wounding a tree’s roots creates points of entry for pathogens, leaving a tree vulnerable to disease. Cutting major roots also reduces a tree’s ability to absorb nutrients and water, leaving it more susceptible to drought. In addition, cutting roots can reduce a tree’s structural support, which increases the danger the tree will topple onto your house in high winds.
When cutting problem tree roots, remember:
• The farther you cut from the trunk, the less threat to the tree’s health, and the less danger of creating a hazard.
• Avoid cutting roots greater than 2 inches in diameter.
• Prune roots back to a side or sinker root (one that is growing downward) when possible.
• Roots recover from being severed when you cut them cleanly with a saw, instead of breaking them, and mulch and water well after pruning.
• Consult a qualified arborist when cutting within a distance equal to five times the trunk diameter to the trunk.
To avoid cutting tree roots altogether:
• Install physical root guides and barriers that redirect tree roots down and away from hardscapes with minimal impact on the tree.
• Curve new hardscape features, such as a driveway or patio, around the tree roots.
• Suspend hardscape features on small pilings to bridge over roots.
Ultimately, the best way to keep the trees and their roots on your property from causing damage is to select species that match site conditions, Andersen says, and to avoid planting large shade trees within 12 feet of hardscapes. In areas within five to seven feet of a paved area or structure, plant trees that grow to a mature height of less than 30 feet. In areas within seven to 10 feet of a paved area or structure, plant trees that grow to a mature height of less than 50 feet. Reserve trees that mature to higher than 50 feet for areas with at least 12 feet of clearance around the trunk; this allows adequate space for the roots.
A professional arborist can assess your landscape and work with you to determine the best trees to plant.