We have all seen thinning grass under large street trees; large surface roots that cause safety hazards and mowing obstacles; and tree trunks damaged by lawn mowers or trimmers. These situations can be caused by trees and grass growing too closely together. Most tree roots are in the top two feet of soil. More important, the majority of smaller, water-absorbing roots are in the top six inches of soil. Thus, trees and turf compete for sunlight, water and rooting space. In addition, raised soil at the ground level of street trees is due to the swelling of the base of older trees.

Mulching the area around trees eliminates potential competition. A 2- to 4-inch layer of wood chips, bark or other organic material over the soil, under the tree's drip line is suggested. If the mulch is any thicker, water and oxygen cannot reach the roots as easily and surface roots or girdling can occur.

Do not place the mulch against the trunk of the tree, contrary to common landscaping practices! The mulching assists in retaining moisture, reducing weeds, increasing fertility, improving appearance, protecting the tree trunk and improving soil structure. Mulching too high against the trunk of the tree may cause the bark to rot or it can girdle the tree. Both of those conditions can cause premature death of the tree.

Surface roots are often wounded by lawn equipment. As roots provide mechanical support in addition to water and nutrient uptake, damage to trees roots can eventually lead to a larger problem, an uprooted tree.

Watering newly planted street trees is an important part of establishing deep root growth. Water long and less frequently, letting the soil become moist to a depth of several feet. This will help prevent surface roots that may result from shorter, shallower watering. One inch of water per week is recommended, applied slowly within the entire drip line (the area under the spread of the tree's crown) and just beyond. You may want to water from a gently running garden hose for four to six hours on a weekly basis.