Question
We need to cut away some large roots around our river birch its raised the landscape and is causing water to drain back toward our house. we love this tree will it destroy it?

Josie

Answer
The percent of the roots that are cut is the determining factor. The roots of a tree will extend about 1 1/2 times the width of the branches. A tree can survive root cutting if the amount of roots cut does not exceed 25-30% of the root system. This includes adding soil over the root area or taking soil away from the root area. The root system can be measure roughly by drawing a circle around the tree where the ends of the branches hang and then estimate the area to be cut or filled and calculate the percent damage. The roots will extend further than the branches but these will be smaller and can with stand cutting.
IF you cut a large roots you can expect some foliage dieback on that side of the tree. You have cut the root that supplies the food and water to the foliage and the tree will drop some of the foliage to compensate for the root loss. You can cover the exposed roots as long as you do not put more than 3 inches deep of sand over the exposed root. You maybe able to put sand down and sod to direct the water away. Without seeing the area It is hard for me to make that determination.
IF covering is not an option then cut the root but try to stay out from the trunk as fart as possible. And after the cutting I would water once a week with 1 inch of water--place a pan under the tree and turn the sprinkler on and when the pan has 1 inch of water in it stop. This will encourage new root growth and help the other remaining root to have more water for the foliage.