It's easy to think that your Bradford pear (Pyrus calleryana "Bradford") has it in for you. Not only do its flowers smell -- not in a good way -- but its branches break easily, and the tree has surface roots that seem designed to spoil your grass and make you stumble. While removal is an option for the long run because Bradford pears generally live only 15 to 20 years, covering pesky surface roots too deeply can lead to an early demise.
About Bradford Pear
Bradford pears, also called callery pears, grow in full sun in U.S. Department of Agriculture plant hardiness zones 5 through 9. They grow from 30 to 50 feet tall with a spread of 35 to 40 feet. Branches are densely packed and tend to break off, and the heavy shade the tree creates tends to shade out grass and other plantings. The tree has a shallow root system.
Where roots emerge from the soil, they can send up shoots. Planting too deeply can cause a Bradford pear's roots to grow around the trunk, essentially choking the tree until it dies. Moisture can be held around the root flare -- where the roots meet the trunk -- by soil or mulch and cause the tree to rot at the base. A root system that is buried too deeply may not get the water, fertilizer or oxygen it needs. Roots can also push up into added soil or mulch and cause the original, deeper roots to die back, leaving the tree vulnerable to drought stress and storm damage.
When planting a Bradford pear, the root flare should be 1 to 2 inches above grade. This doesn't always mean planting the root ball at the same depth it was in the container -- sometimes soil has been added to the top of the pot at the nursery. Always look for the root flare and expose it as necessary. Adding soil over the root zone to sow grass seed or plant garden plants isn't recommended. The dense canopy of a Bradford pear shades out most plants anyway.
Applying mulch over the root zone of a Bradford pear can prevent shoots as well as retain moisture, stop weeds and prevent a tripping hazard. This Old House recommends removing excess mulch and soil from around over-mulched trees and reapplying 1 inch of mulch over the root zone -- keeping the mulch back at least 3 inches from the trunk -- each year for three years. At the end of three years, clear off the mulch and begin again with 1 inch. You can lay down 2 to 3 inches at once, but no more than 3 inches at any one time. The mulch should extend to the edge of the tree's drip line, or at least 2 feet for every inch of trunk diameter.