Any home owner who has gotten a notice from the City of Portland to repair their sidewalks or else knows how contentious of a battle it can be for trees and sidewalks to co-exist in the city. Not only are the quotes from concrete contractors enough to make you sick the thought that due to your street tree’s roots you may have to do this again in a few year is just about enough to drive you over the edge. I wish I had some miracle cure all solution to ease the pain, but unfortunately when it comes to controlling tree roots there is only so much that can be done.
What not to do
- Do Not cut a tree root or let your concrete contractor cut one. Tree roots that need to be cut must be marked by the city arborist prior to cutting. Cutting them without this approval is a surefire way to cause permanent damage or death to your street trees and to buy yourself a hefty fine from the city. This includes the method of carving an “X” on the top of the tree root (which does not work, by the way). Studies show that despite tree root pruning, sidewalks will, on average, lift again within five years without the use of other root control methods.
- Do Not Heavily prune your tree or use tree growth inhibitors. Heavy pruning is expensive and most of the time does not work. When tree growth inhibitors are used energy that would normally go the development of the crown of the tree is often redirected to the root system when these methods are deployed therefore further aggravating the problem.
- Do Not Assume you need to replace your concrete. Concrete contractor have other options and it you are going to end up doing this again in a few years due to new root growth you may want to hold off if there are other options available to you such as concrete grinding and/or patching.
- Do Not Wait. If you get a notice from the city it usually gives you a extended amount of time to correct the problem. They do that for a reason, because it takes an extended amount of time to arrange all the permitting and the work to get done.
As with many things the solution starts with prevention. The type of tree planted is big determiner if you are going to have root problems in the future, as is if the tree is planted correctly. You can review our blogs posts under tree planting for advice on choosing and installing a tree correctly. Additional options such as root barriers can be installed when trees are young to direct the growth of roots. Sometimes it is better to remove existing trees, start over, and get it right the second time. Of course you will need the city arborist’s blessing to do this.
Nothing will determine your success in dealing with the invasion of growing roots more than choosing the right concrete contractor when repairing or replacing your concrete. You need a contractor who is willing to use a complete arsenal of tactics to repair the current problem and prevent a re-occurrence. These methods include but are not limited to the use of pea gravel which allows tree root to expand, reinforcing concrete with rebar so that the tree root must lift several slabs at once in order to cause damage to the sidewalk, creating a meandering sidewalk or a side walk with cut outs to create more space for roots, and create slightly sloping sidewalks to allow elevation change due to root growth.The example to the left shows a slightly arching sidewalk with cut outs for tree work growth. Home owner should also explore the option of having sidewalk repaired or ground down instead of removed and replaced to limit their investment. A knowledgeable concrete contractor will explore all of these options with you including repair.