Notching a large tree root
We have a very large Cottonwood growing on our boulevard. One of its roots has lifted up a section of sidewalk which has to be replaced. What is the best way to notch the tree root (so the sidewalk can be poured flat) before pouring the sidewalk? We don't want to hurt the tree, but the city is requiring us to flatten out the sidewalk. Any advice?
Ward County North Dakota
There is no painless solution. You need to decide if you love the tree or love a new sidewalk.
A cottonwood is a terrible choice for a boulevard tree. It is much too large and aggressive. But there is nothing we can do about it now.
If you love the new sidewalk, you need to cut the root that is heaving the sidewalk. What else can be done?
Make a clean cut. Wound dressings are not needed.
Minimize the amount of digging. This includes the depth of the digging and the expanse of the digging around the tree. Under the best case scenario, you will destroy about 25% of the tree's roots.
Minimize compacting the soil around the tree due to the use of heavy equipment. Minimize any damage (scraping) to the bark due to the use of heavy equipment. This will protect the roots you do not destroy.
Yes, this will hurt the tree. It will not likely kill the tree, but you will cut off a good amount of its roots. The tree will show reduced vigor, but will likely survive. The reduced vigor can be compensated by watering and fertilizing the tree, if you wish. Maybe a spring fertilization and then water whenever we have drought spells for the next two to three years.
A cottonwood is an adaptable tree. It is not overly sensitive. It should survive this "surgery". Just minimize the pain and protect as much of the root system as possible.
If you don't want to hurt the tree, live with a raised sidewalk.
Gary Johnson of the University of Minnesota has a lot of information published on tree care in urban environments (Urban forestry). You many wish GOOGLE him to find some related information.
Let me know if you have any more questions.