September 13, 2019

How to design and build a retaining wall near a tree and not kill it?

Written by Jeremy Zeis

Three steps to make sure your tree survives retaining wall construction.

It’s time to design that retaining wall that you’ve been wanting for a while now, but there’s just one problem; your favorite tree is standing in the general area that the new wall will be. Construction can be a brutal process and you aren’t sure if your beautiful tree will be able to survive the stress that putting up a retaining wall can create. Well, fortunately, we’ve got some good news for you. Along with some proper planning, the following three steps can be used to ensure that your tree will survive well beyond the construction and installation phases of your new retaining wall.

1. Talk to an arborist.

            We may be experts on retaining walls, but when it comes to trees we’ve got nothing on arborists. These tree professionals are the perfect people to consult about any specific needs that your tree might have when it comes to surviving retaining wall construction. They’ll be able to give you a general idea of what impact the changes you’re making will have on the existing trees and how easy it will be for them to adapt. If asked, they can also share some tips and tricks to monitor how healthy your tree is and what you have to do if it’s showing any warning signs.

 2. Be mindful of your tree when designing your wall.

  Trees need space. With roots that grow out in every direction, trees can take up a lot of ground space, but how much do they need in order to stay healthy? The most important area of the tree’s space to protect is the Critical Root Zone (CRZ). The CRZ is where the majority of the tree’s major root systems begin. This zone can be estimated by tracing the canopy of the tree onto the ground (the dripline) as seen in Figure 1. If you want your tree to survive, it is important to design your wall in a way that avoids interfering with the CRZ This can be done by curving your wall around the zone.

3. Avoid the Critical Root Zone during construction.

Not only is it important to avoid the CRZ with your design, but it’s also important to be mindful of it during construction. In order to maximize the chances of your tree surviving construction, any of the following actions should be avoided within the CRZ if possible:
·       Any soil compaction
·       Changing grade
·       Parking heavy machinery
·       Material storage
·       Digging into soil and damaging the tree’s roots

As you can imagine, even if they take place outside of the CRZ, any of the above actions will still affect the tree’s health, just not as severely as if they happen inside of the zone. It’s also important to note that not all trees will react to changes in their growing environment the same way, so be sure to find out how your specific tree will be affected.

In addition to the three steps above, we encourage you to learn more about proper retaining wall construction so that your favorite tree and new wall can both live healthy lives for decades to come. 

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