What’s the problem?

• Trees often ruin sidewalks, and sidewalk repair often kills trees.
• This conflict comes from the fact that sidewalks and trees have competing needs.

• Trees need a soil that is moist and loose, and that they can push aside as they grow.
• Sidewalks need to be smooth (but not flat) on a soil that will not shift with a load.

• Trees and sidewalks are costly and valuable, so both needs must be taken seriously.

• Most of the damage to sidewalks is caused as roots become thicker through secondary growth.

• Sidewalk damage is often caused not by the tree but by the soil in its expansion and contraction.
• The buttress roots supporting the tree cause the worst damage.
• Roots often follow cracks, because there they find the water and air they need.

• Most of the damage to trees comes when the main roots are cut close to the trunk.

• When larger roots are cut, trees lose mechanical support from that side, and become more likely to cause harm from windthrow.
• Main root cutting also heavily reduces the flow of water and nutrients to the crown, causing especially older trees to die in 3-5 years.

                                                      Buttress roots of sugar maple cut for sidewalk replacement

• If a tree is in poor condition, it is best to remove the tree and replace the sidewalk.
• For trees in good condition, a sidewalk can be curved around the trunk (at least 2-3').
• In some cases, a raised edge can simply be ground down, or smoothed over with asphalt.
• The new sidewalk may be ramped up and over the roots by starting further away.
• You can also do minimal excavation, and then pour asphalt directly over the roots.
• Gravel, mulch, pavers set in sand, or asphalt can be used instead of concrete.

• 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 over 2" in diameter.
• Roots recover better from being severed when you

• cut them cleanly with a saw instead of breaking them with a backhoe
• protect them from drying out while work is going on
• mulch and water well afterwards
• provide slow-release fertilizer in early fall or spring

• Provide enough space for the species you want to plant.
• Try to keep large-growing trees in tree lawns 10' wide or greater, medium trees in lawns 6-10' wide, and small trees in 4-6' lawns. Avoid planting trees in lawns under 4' wide.
• Give species with many large surface roots (like Norway maple) lots of room.
• You can't necessarily rely on root barriers--the roots do grow down, but then often come right back up!
• Consider experimenting with a structural soil mix that will better tolerate root growth.

Fazio, James R., Ed.  1991.  "Resolving Tree-Sidewalk Conflicts."  Tree City USA Bulletin 3.  Nebraska City, NE: National Arbor Day Foundation.  Anonymous.  1995.  "Trees and Sidewalks."  Iowa State University.  For other information, advice and help on this topic, call offices of your State Urban Forestry Coordinator or University Extension service, visit urban forestry web sites.