How to Correct Aggressive Tree Roots

Trees are hardy plants, and their roots fight back against man-made limits around them. In the urban and suburban landscape, tree roots often are forced to grow between buildings or under driveways and walkways. As roots grow, they can break walls, pipes and patios, causing damage to properties.

Plan Before You Plant

“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,” advises Tchukki Andersen, Board Certified Master Arborist, CTSP, 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 – putting them in conflict with man-made obstacles. Where the soil is covered by a solid driveway or patio, upward growing roots don’t experience the normal signals (increased light and air) that tell them they are reaching the surface. As a result, they often grow against the underside of pavement and become intrusive.

“Most damage is found 6 feet or less from the tree since roots become smaller and less damaging the farther they are from the trunk,” notes 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.”

Cutting Roots with Discretion

Some homeowners, masons and landscapers deal with intrusive roots by grinding down or removing them. This can be expensive and is very 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 take up nutrients and water, leaving it more susceptible to drought. Finally, cutting roots can reduce a tree’s structural support, which increases the danger that the tree will topple onto your house in high winds.

Keep the following in mind when cutting problem tree roots:

• the farther you cut from the trunk, the less threat to the tree’s health, and the less danger of creating a hazard
• try not to cut roots greater than 2 inches in diameter
• prune roots back to a side or sinker root (growing downward) when possible
• roots recover better from being severed when you:
  • cut them cleanly with a sharp saw instead of breaking them with a backhoe
  • mulch and water well after root pruning
• consult a qualified arborist when cutting within a distance equal to five times the trunk diameter to the trunk

Some better root management options include:

• installing 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

Right Tree for Your Site

Andersen advises selecting trees for your landscape that will cause less damage, matching species with site conditions and – most importantly – not planting large shade trees within 12 feet of hardscapes (sidewalks, driveways). Since the health of trees in your yard is put at risk whenever root systems are cut back or damaged, anything that can be done to reduce the damage caused by tree roots will also benefit your trees. 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 when mature reach higher than 50 feet for areas with at least 12 feet of clearance around the trunk; this allows adequate space for the roots. Finally, before you plant, check for overhead utility lines and leave adequate space for that tree to mature.

Image Credit: William Fountain, University of Kentucky, Bugwood.org