Trees set in an urban environment are essentially out of their element. The forest is the natural habitat for trees and because of that offer many benefits that an urban setting does not. One of the primary benefits is the upper soil layer in a forest is composed of 8-12 inches of decaying leaves, twigs, insects and many other important biological elements. In your yard however these debris are typically removed so the grass can grow green and healthy. As a tree grows up in this environment, essential nutrients are used up and not replaced by the debris layer found in the forest. This leads to a gradual decline to the health and vitality of the tree. One way to avoid this and provide a healthy soil for the tree to grow in is to add a layer of organic mulch around the tree base.
Organic mulch is any type of mulch consisting of once living plant life. Typically the best organic mulch is composed of a mixture of shredded leaves, broken twigs, and tree bark. Organic mulch slowly degrades into the soil replacing essential nutrients and also provides a home for beneficial insects. It is important that the mulch is applied properly otherwise it can be harmful to the tree health.
Mulch should be spread no thicker than two to four inches. Any thicker than that and the mulch will hold too much moisture and be a breeding ground for harmful fungi. Also when mulch is piled to thickly poor drainage and soil aeration can result. Typically a healthy mulching regimen will extend the mulch out to the drip line of a tree. In an urban setting this may not be practical however but don't let that discourage you. Remember to never pile the mulch directly against the tree bark or root flare, give the base of the tree several inches of clearance to avoid fungal infections.
Other benefits of mulching include not have to expend extra energy mowing around exposed roots and the trunk of the tree. Also there would be no need to weed eat against the tree and thereby no weed eating scars could be left. When done properly, mulching along with a proper border can add aesthetic and monetary value to your yard.