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How to correct aggressive tree roots

Friday, June 8th, 2012
Issue 23, Volume 16.

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 will break walls, pipes, and patios, causing damage to properties.

"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," said Tchukki Andersen, board certified master arborist and staff arborist with the Tree Care Industry Association.

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 dont experience the normal signals (increased light and air) that they are reaching the surface. As a result, they often grow against the underside of pavement and become intrusive.

"Most damage is found six feet or less from the tree," said Andersen. "Since roots become smaller and less damaging the further they are from the trunk. 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 trees roots creates points of entry for pathogens, leaving a tree vulnerable to disease. Cutting major roots also reduces a trees ability to take up nutrients and water, leaving it more susceptible to drought.

Finally, cutting roots can reduce a trees structural support, which increases the danger the tree will topple onto your house in high winds.

Keep these cautions in mind when cutting problem tree Advertisement
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• 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 two 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 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 hardscape 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 the site

Andersen advises selecting trees for a 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. Also, before planting, check for overhead utility lines and leave adequate space for that tree to mature.

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