Grass and trees are fierce competitors for oxygen, nutrients, water and sunlight. That’s why you seldom see nice healthy trees and grass in close proximity to each other. Usually one or the other will be dominate.
In the urban environment, sod is often placed over the root system of a tree and it generally has the advantage obtaining nutrients and water. If the grass is thick, these much need items are all but unavailable to the tree. However, the tree probably has the advantage when it comes to sunlight. If left on their own, the tables will turn and the tree may get the upper hand as leaves and twigs fall and begin to smoother out the grass. But they are rarely left on their own because the leaves are raked and discarded most of the time.
One way to have the best of both worlds includes a little compromise, but the results are good for both the grass and the tree. Avoid the competition with a little separation. Do this by removing the grass and placing a two to three inch layer of wood chip mulch over the root system of the tree out to the drip line (edge of the canopy). The mulch not only adds a source of organic nutrients for the tree, it regulates soil temperatures, holds moisture in the soil and discourages grass from encroaching. Give it a try.
Written by Paul Martin, ISA Certified Arborist