The grass actually competes with the tree for water and nutrients. Scatter fertilizer around a tree and you will end up with very healthy grass. Tree food stakes inserted into the ground release nutrients below the grass layer. Use fertilizers specifically designed for shade or elm trees. Also, take care when mowing.
Lawn mowers can damage a tree.
Better yet, avoid the problem by keeping the grass back from the base of the tree. A buffer zone of loose soil or mulch is ideal. Watering In an elm, the tips of the roots are usually located outside of the weeping or drip line. This is the outermost extent of the crown of the tree. Therefore, sprinkling water onto the trunk will have little or adverse effect on the tree's health.