I recently bought a house and the grounds were professionally landscaped, so all the trees have mulch circles around them of about 6-12 feet in diameter depending on the size of the tree.
Originally these circles were mounds at the base of the containing only mulch and devoid of anything else.
In the last couple of years, grass from the surrounding lawn has started to infiltrate these circles and fill them up.
Should I allow this to keep happening and have grass grow into the area around the trees, or is there a reason to keep grass away from the base of the trees and maintain the mulch mounds?