Digging a circle around your tree isn't just for looks. There are very practical reasons to remove turf from around the trunk. Grass competes with trees for water and resources and gives nothing back of value. Mulch is a much better option and can protect the tree from disease, drought, harsh climates and even the stray lawnmower blade. By digging out a circle and filling it with mulch, you not only give your landscaping an aesthetic boost, but you also give your tree a health boost.
The ring around a tree should be extended to the dripline, or the invisible line where water literally drips from the tree branches when it rains. This is generally the span of the bottom branches. Within this circle, water is delivered to the rootlets which feed the tree. Mulching around this circle will help to disperse the nutrients and water evenly, rather than only to the roots immediately near the trunk, thus preventing trunk rot. For extremely large trees, extending the mulch ring to the dripline may not be practical. It may not only diminish the useful areas of your yard, but labor and cost could be prohibitive. A circle with a radius of 12 feet will still provide many of the benefits of a full dripline circle.
Creating a Compass
Tie a length of twine around the tree's trunk and unravel it as far as the dripline. Tie the open end to a garden spade. Use the trunk and twine as a compass point and push the spade in the ground. Work around the tree, pulling the twine taut as you go, and push the spade into the ground over and again to create a visible circle along the dripline. This indent will give you an even border for your ring and a starting point for pulling up the turf grass.
Digging out the Grass
Use the spade or a square-tipped shovel to begin lifting the turf grass, starting at the indent of your circle and working in. Push the spade about an inch below the grass and pull up as much of the root system as possible, rocking the spade to separate the sod from the earth. It may be better to think about "lifting" the grass rather than "digging." Work through the entire circle, but take extra caution when you reach the area near the trunk and around high-growing tree roots. Do not dig into these sensitive areas of the tree, but try to lift and roll up the sod with the shovel as you go. Some deeply-rooted weeds may need to be removed by hand.
Mulch should serve to recreate the natural conditions in a forest. The "mulch volcanoes" that gained popularity in recent decades have proven to be more of a detriment to tree health than a benefit. Chose an organic or composted mulch product and spread 2 to 4 inches of mulch around the tree, or less if you know the area has poor drainage. Mulch should rest around the tree in a natural fashion and be spread evenly so it just touches the natural root line of the tree without spreading up towards the trunk or over the root crown.