Reducing root size on large locust tree during sidewalk replacement - urgent - Ask Extension
New sidewalk will be poured 8/3.I have to repair sprinkler lines going under a sidewalk. The sidewalk has been removed. I exposed several large ro...
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Reducing root size on large locust tree during sidewalk replacement - urgent #670134
Asked July 28, 2020, 10:56 PM EDT
New sidewalk will be poured 8/3.
I have to repair sprinkler lines going under a sidewalk. The sidewalk has been removed. I exposed several large roots about 4'-5' away from the trunk so I could see what we're dealing with both for the tree and sprinkler system. The large roots caused the sidewalk to heave. Can I trim off the top third to half of the roots so we can get the 4" thick sidewalk poured to be level with the existing sidewalk? Tree is 40-50 years old. I don't want the concrete contractor applying a chain saw to the problem.
Arapahoe County Colorado
Expert Response
Hi, thanks for contacting Colorado Extension Ask an Expert.
Thank you for sending in images of your tree and the sidewalk,
Tree roots crack sidewalks as the roots grow and expand in girth. However, that primarily occurs close to the tree--within about 10 feet. The biggest surface roots are immediately beside the tree. To avoid the sidewalk/tree root issue in newly planted trees, it will depend on your tree and how good your soil is. In good soil, roots do not need to be as close to the surface, they grow deeper. But, most tree roots are always in the top 18" to 2 feet of soil. See Plant Talk # 1507 https://planttalk.colostate.edu/topics/lawns/1507-tree-roots/ and https://extension.colostate.edu/topic-areas/yard-garden/healthy-roots-and-healthy-trees-2-926/
Unfortunately, if you any cutting on large tree roots harms the tree and is risky to large established trees. Cutting off a small root (small roots should not cause the cracking and heaving you mentioned in your question) should not cause serious harm to the tree.
You could try to dig a trench 12 to 24 inches deep with a width of at least five feet and bury the root of the tree to try to redirect it to grow deep under the sidewalk, eliminating the heaving caused by roots just under concrete. However, remember most tree roots are always in the top 18" to 2 feet of soil so they can supply water and nutrients to the tree so if you bury deep under the proposed sidewalk, you risk distressing an established tree which causes further problems.
Sorry I could not give you a definitive solution, other than do not shave or cut large roots of established trees.
Thank you for sending in images of your tree and the sidewalk,
Tree roots crack sidewalks as the roots grow and expand in girth. However, that primarily occurs close to the tree--within about 10 feet. The biggest surface roots are immediately beside the tree. To avoid the sidewalk/tree root issue in newly planted trees, it will depend on your tree and how good your soil is. In good soil, roots do not need to be as close to the surface, they grow deeper. But, most tree roots are always in the top 18" to 2 feet of soil. See Plant Talk # 1507 https://planttalk.colostate.edu/topics/lawns/1507-tree-roots/ and https://extension.colostate.edu/topic-areas/yard-garden/healthy-roots-and-healthy-trees-2-926/
Unfortunately, if you any cutting on large tree roots harms the tree and is risky to large established trees. Cutting off a small root (small roots should not cause the cracking and heaving you mentioned in your question) should not cause serious harm to the tree.
You could try to dig a trench 12 to 24 inches deep with a width of at least five feet and bury the root of the tree to try to redirect it to grow deep under the sidewalk, eliminating the heaving caused by roots just under concrete. However, remember most tree roots are always in the top 18" to 2 feet of soil so they can supply water and nutrients to the tree so if you bury deep under the proposed sidewalk, you risk distressing an established tree which causes further problems.
Sorry I could not give you a definitive solution, other than do not shave or cut large roots of established trees.
I had two arborists look at the situation. Both said it was OK to remove the roots given the age and health of the tree. Given the tree's size it was permissible (not desirable) to trim up to 20% of the roots without serious damage to the canopy.
Also, given the age of the tree the root was not essential for tree stability. One hopes...
They recommended generous winter watering in any case.
The root is far to thick (4") to point it in a different direction. Digging up the rest of the landscape to redirect the root is not realistic I'd say.
Thanks for your input.
