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To curb or not to curb?

Instead of installing curbing around a parking lot island or median strip in the traditional manner, consider placing the curb on top of the pavement edge.

traditional curbing design and alternate design diagram

A Curbs designed in the traditional fashion often deflect roots laterally and under the curb. This can result in broken curbs as roots enlarge.

B Curbs placed on top of the pavement may allow more roots to grow under the pavement and could be less expensive to install. They can be constructed from concrete, treated wood, or synthetic materials.

Curbing can be constructed from treated wood, which is lighter than concrete, to prevent pavement sag. Also consider building islands without curbs or with only shallow curbs. Deep curbs often deflect roots, preventing them from growing beneath pavement, which also restricts root growth and stresses the trees. Building parking lots without curbs around islands could increase tree health by allowing more roots to escape the island and grow beneath the pavement.

A possible disadvantage of this is that the property owner might perceive the raised pavement near aggressive surface roots a hazard. Crack created by roots also allow water to enter the soil beneath the pavement; freezing and thawing in cracks then causes further pavement damage.

But remember, most pavement cracks after it is installed, often without help from the trees! If pavement remains intact, trees are growing poorly.