Tree Rings - Not Just for Looks
Tree rings in this article are not the ones inside the tree that you count to determine how old the tree is, but rather the maintenance practice of removing the lawn away from the trunk of a tree which has been planted in a lawn area.
First of all, planting trees in lawn areas is not advisable because trees and turf have drastically different watering needs. But if you do have a tree growing in a lawn area, it is a good idea to make a "tree ring" by removing the grass from around the trunk of the tree. This can be done for any tree, regardless of age. The size of the ring should be determined by how large the tree is. It looks good to keep the tree ring roughly as big as the tree's canopy - up to a point - eventually there may not be any grass left if the tree is a large mature specimen. For a newly planted tree, a three-foot diameter ring is generally a good starting point. Expand the diameter of the ring as the trees grows, until it gets to be 15 to 20 feet, or until it interferes with some other boundary in the landscape.

Start by using a tape measure to measure an equal distance all the way around the tree. Mark the ground as you measure around the tree until you have a circle. Use a sharp shovel or spade to cut straight down into the grass about four inches all the way around the circle, then remove the grass inside the ring with a flat shovel or mattock, being careful not to damage the tree trunk in the process. Add a 3 - 4 inch layer of mulch on top of the exposed soil to shade the tree roots and help retain moisture in the soil. Maintain this mulch layer by occasionally adding more as necessary, but never pile it up around the trunk. "Mulch volcanoes" if left too long, can actually kill the tree. Maintain the ring edge by whichever method you prefer - curbing, plastic or metal edging, or by simply cutting it like a planter bed.

Not only are tree rings more aesthetically pleasing, but they are good for the tree. When the tree is young there is less competition with turf for water. Tree rings also reduce the chance for mechanical damage to the tree from lawn maintenance equipment ("weed-eater blight" and lawn mower hits).
- Courtney