Proper Tree Mulching
While it is common to see 4 to 6 inches of mulch around a tree, this is usually too much. I would suggest 2 to 3 inches placed in a ring around the tree with the center around the trunk empty, kind of like a doughnut. How wide to make the ring is up to you, but the farther the better. Trees don’t like to compete with lawns for nutrients and water, and the more mulched area you can give them, the better off they will be. Mulched trees have fewer problems than trees growing in lawns. Even a small, 2 to 3 foot ring can make a big difference. The mulch creates a more natural growing environment with its organic material breaking down and supporting vital soil microbes. Other benefits include increased moisture retention and cooler soil temperatures, both of which favor optimal root growth.
If done properly, mulch is a great asset to your landscape and aids your trees during summer drought periods by maintaining soil moisture. It also helps insulate the roots during the winter months, which allows them to remain active longer into the season. http://ow.ly/i/1XIVk