Where to Plant a Street Tree?

We hear a lot of discussion about the need to increase urban tree canopy, and the area people often focus on when planting new trees is the strip of land along the street in front of homes or businesses. This strip is known as a planting strip, buffer, neutral zone, park strip, or in Great Britain, a verge. These long strips of land often contain just grass and appear empty, making them seem like ideal spaces for planting trees. In most urban areas, however, planting strip conditions above and below ground may surprise you.

Our streets accommodate water, sewer, storm, gas, power, and communication infrastructure and we use strips as a place to install wayfinding signage and lighting. These utilities render the areas underneath streets very complex and crowded places. Often, it’s difficult for trees to find the space or quality soil that allow them to grow strong roots and mature into large conifers and broad leaf trees.

Even after 40 years in this field, I find placing trees in the right of way quite puzzling. Recently, I was preparing for what I thought would be the simple task of selecting and placing trees along a street that had none at the time. There were requirements in regard to spacing and minimum number of trees, but with 1200 feet of street space it didn’t seem like the requirements would be a problem. Wrong. There was a utility every place I looked. I needed to stay 5 feet from water mains and driveways and away from gas lines. There was an underground communications duct bank to avoid and a light pole with a setback of 25 feet. I finally found an open spot big enough for a large tree, only to realize that there was also a hydrant in the space and a requirement to keep at least 10 feet between tree and hydrant. Jeepers, where are trees to go? I located an alternative, seemingly open space and wouldn’t you know – the water and sewer services to the houses were in the same spot.

After many iterations, space was found but it was only big enough for a small tree. Because of the lack of usable space, the street won’t ever provide the classic feel of overhead branches providing a canopy of leaves as you walk or drive along.

To accommodate the variety of uses of urban streets most cities have developed clearance regulations for underground utilities, and rules vary from place to place. In a review of requirements across the US, Canada and Australia, I discovered a common goal to provide guidance for understanding the location and spacing of underground systems. Most cities and states have defined where utility main lines are placed horizontally, however, the depth of these utilities may vary. In addition, utility lines serving adjacent properties typically cross through planting strips, effectively creating a grid of lines under streets.

As we look to plant trees and even consider installing rain gardens along our streets, we often observe overhead power lines, but we need to also investigate what systems lie under the ground and how far we must stay from them. There are three levels of investigation: 1) the internet – you can often find information on utilities by looking on the local public works web sites,  2) your eyes – go outside and observe surface conditions, 3) formal notice – call the utility notification center 811 or www.callbeforeyoudig.com to locate utility lines along your frontage.

Once you have an idea of where utilities are, it’s important to find out what the clearance requirements are for your location. Clearance requirements must be observed between trees and most utilities, vaults, meters, signs, light posts, pavement types, and other miscellaneous structures. Setbacks are often designated from intersections and driveways and it’s important to pay attention to building entrances and windows. While you might think clearances and setbacks are consistent and based on research, you will find that dimensions vary and are often based on observational judgement and space allowance for potential repairs. Nevertheless, unless you are doing major corridor planting, it is advisable to adhere to required vertical and horizontal setbacks and clearances.

The setbacks that often surprise us are tree clearances between both intersections and street lights. Setting trees back from intersections keeps crossing zones clear so pedestrian and vehicular movements are visible. Street lights often get blocked by trees so planting trees away from the light posts ensures that when the tree develops a mature canopy, it can spread its branches without instigating awkward pruning in the future.

My advice on planting street trees? Look closely, do your research, and if by chance you find that increasingly rare space that will accommodate a large tree – plant it quickly before that space too becomes occupied.

Photos courtesy of MIG|SvR


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