In the city of St. Louis, the average size of a tree lawn–that strip of grass between your sidewalk and the road that you live on–is a relatively narrow 3 to 5 feet wide, with some variation depending on your neighborhood.
The size of the tree lawn is an important consideration because it often dictates the best type of tree to plant. “A lot of the larger canopy trees that we have that are native to the state of Missouri, in their lifetime, are going to outgrow that space,” says Billy Haag, forestry manager with Forest ReLeaf of Missouri. “So, even though we love the large oak trees, maybe we have to scale it back and look at some of those medium-sized trees that are really going to thrive in a smaller area.”
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The site characteristics of each tree lawn, including the amount of sunshine it gets, whether it’s sloped or flat, and if there are existing trees around it that affect the shade and moisture of the area, are also important factors to keep in mind. “There’s a lot of things to consider and based on those site characteristics that’s how you’re going to choose the right tree to match that spot,” he says.
Planting the right tree in the right place is a first step to finding success with trees, in general, but understanding its purpose, whether the resident is more focused on air quality, fall color, or spring flowers, is also key to determining the best fit for you.
In other words, take your time before making your selections.
Additionally, there is the weighty issue of heavily compacted soil and ground on a tree’s root system that grows under a sidewalk or near a street. “Roots systems are not a mirror image of the tree’s canopy,” says Haag, “but in reality can stretch two to three times the width of that tree canopy in the first inch or foot and a half of the soil level. When they’re competing against compacted soil and ground, it’s going to be a little bit tougher for them to spread their roots where they want to go,” he says.
So, can trees that are planted on a sidewalk truly thrive? “I think we can get them to live there, but with those extra conditions of pollution, urban heat, as well as compacted soil, it’s going to be a tougher life for those trees,” says Haag.
Yet, street trees are vital to a city, especially in relation to their proximity to where people live. “From air quality improvement, to flood reduction, and providing shade, our trees are so valuable to human health and to our city’s infrastructure. We need street trees.”
Rethinking what a tree lawn looks like and how humans can help trees survive will keep both trees and the community healthy.
Diligent watering, for example, five to 10 gallons once per week for the first two years after planting is one of the best things any one can do for a tree. Limiting compaction under sidewalks through the use of silva cells is also helpful. The City of St. Louis incorporated this system when they redid the sidewalks near Jefferson.
“They were able to plant larger trees and then do the sidewalk on top of that,” notes Haag. “Now that the sidewalk is there that silva cell is right underneath it, limiting compaction so [the soil] is nice and loose, and those establishing trees are having an easier time reaching their roots into fresh soil.”
For those who might consider planting something other than a tree, think perennials, wildflowers, and grasses. “But nothing that’s getting too tall because that is a fairly skinny area,” says Haag, “and our prairie plants are just going to flop over onto the sidewalk and cause conflict with pedestrians.”
