It hardly seems possible, but we are already back to another ideal tree planting season in Seattle. As the cooler temperatures and more frequent rainfall return, conditions are great for giving newly planted trees the best chance of establishing themselves and thriving. Healthy trees are a great asset to any property and to our city in general. They provide beauty, wildlife habitat, cool shade in summer, and help to mitigate the stress on our storm sewer system with their uptake of water.
Right now, we are going back to some job sites from earlier in the year to install street trees in the city-owned rights of way (ROW). In these instances, the city inspectors, the builder clients, and the vendor nurseries all agreed with us that it would be better to wait for the cooler days of autumn to plant trees rather than take extraordinary measures to properly water new trees during the late summer heat.
SDOT Is a Resource
Over the past year, we have learned a lot from the urban foresters at the Seattle Department of Transportation (SDOT). This city agency owns the planting strips, or rights of way, between the sidewalks and the curbs along city streets, and is responsible for ensuring that all ROW plantings meet the required standards. They have stepped up to help by inspecting trees and their root balls for good structure and general health before planting, rather than waiting until the trees are already in the ground. In some cases, they have gone out of their way to help locate difficult-to-find specimens at nurseries throughout the Pacific Northwest.
Besides the list of acceptable tree species and varieties for the ROW, there are also extra soil amendment and root barrier requirements. Soil amendments are generally required at a minimum depth of twelve inches. In the ROW, if a new tree’s root ball is deeper than that, the amendment is required to match the root ball’s depth. This can make for another hour’s worth of work, but in the long run it will boost the tree’s chances of thriving in its new environment.
Protect the Concrete
We have all seen city sidewalks that are buckled and broken by the slow strength of a mature tree’s root system. To prevent such damage and expensive repairs, SDOT requires root barriers along the edge of sidewalks close to new tree plantings. Generally, the requirement is eight linear feet of plastic barrier centered on the tree trunk, to a depth of twenty-four inches. Depending on the width of the ROW, sometimes a barrier is required on the curb side, too.
By meeting SDOT’s street tree requirements, landscapers and homeowners will be giving their new specimen its best chance to thrive and grow, helping to beautify our city, and saving repair costs in the decades to come. See the links below for more information about planting street trees in Seattle.