Picking a Tree for a Narrow Sidewalk Strip

A sidewalk strip is one of the hardest places a tree will ever grow. The roots have little soil, the crown meets wires and buildings, and the pavement gives off heat. Most street trees that fail were simply the wrong choice for the space. A few checks before planting make a large difference to how long a tree lives.

Urban green space, from the I Hug Trees image library

Start with the size it will become

Nursery trees are small, so it is easy to forget that a young maple or fig will one day be many metres tall and wide. Look up the mature height and crown spread of any species you are considering, then compare them with the real space: the width of the strip, the distance to the building and the height of the nearest wires.

Very narrow strips, roughly a metre across, usually suit only trees that stay small. Where the strip is too tight for any tree, a wider bed, a curb extension or a tree pit with more soil beneath the paving can solve the problem better than forcing a large species into a small slot.

Look above and below the ground

Overhead wires are the most common reason a street tree is cut back year after year. Under a power line, choose a species that stops growing below the wire height, instead of one that will be pruned into a lopsided shape every few years.

Below the surface, check for pipes, cables and compacted fill. Species with shallow, thick roots can lift paving, while deep-rooting trees often cope better. Even so, the best protection for the pavement is plenty of good soil, because roots only run along the surface when the soil below is too poor or too small for them. Our piece on the power of trees in cities explains why that effort pays back.

Match the tree to the street's stresses

Streets bring reflected heat, drought, pollution and, in colder places, de-icing salt. A tree that thrives in a woodland may sulk beside a busy road. Ask local nurseries and the city forestry office which species have lasted thirty years on streets like yours, and favour ones adapted to your climate and soil.

Think about what falls from the tree, too. Heavy fruit, sticky sap and brittle branches become a nuisance on a sidewalk. A clean, sturdy species saves neighbours from complaints and the tree from an early removal.

Do not plant the same tree everywhere

A whole street of one species is at risk when a single pest or disease arrives. A widely quoted guideline is to keep any one species under about 10 percent of a city's trees, any one genus under 20 percent and any one family under 30 percent. You cannot meet that on one block, but you can choose a different species from your neighbour's, and add biodiversity one street at a time.

If you want to see how much cooler a planted street can be, the free Land Surface Temperature tool gives a temperature and greenness report for any point on the map.