Turfgrasses provide many of the same environmental benefits as trees. They
In areas where the lawn is the primary design feature, select woody plants that do the least damage to grass growth and maintenance. The woody plants should be small, have an open canopy (trees that allow sunlight to penetrate to the ground) or have a high canopy. Select trees that do not root near the soil surface; surface rooting is most serious where a shallow topsoil is present. Remember, tree roots get larger as the tree gets older.
While shade is the biggest, most obvious problem trees create for turf growth, a tree's roots also contribute to poor turf performance. Contrary to general thinking, most tree roots are in the top two feet of soil. More importantly, the majority of fine, water absorbing roots are in the top six inches of soil. Grass roots ordinarily occupy a much greater percentage of the soil volume than tree roots and out-compete them for water and nutrients, especially around young trees. However, grass root density is often much lower in areas where trees were established first. In these situations, tree roots compete much better for water and nutrients and prevent or reduce the success of establishing new turf.
Competition is especially important when transplanting, seeding or sodding. The newest plant in the area must be given special treatment and must receive adequate water, nutrients and sunlight. This frequently means that competing sod should be removed from around transplanted trees and shrubs, or that some of the lower branches should be removed from existing trees above a newly sodded lawn. In any case, DO NOT do any deep tilling around trees.
Mulching is an alternative to turf around trees and its use eliminates potential competition. A 2- to 4-inch layer of wood chips, bark or other organic material over the soil, under the drip line is recommended because it:
Many herbicides or weed killers that are used in turf can cause severe damage to trees when misapplied. This can occur on windy days, causing the drift to fall on non-target plants or on hot days when the herbicide may vaporize and diffuse into the air. While most herbicides do not kill tree roots, some, such as soil sterilants and a few others, do. Herbicides that can cause tree damage have statements on their labels warning against using the product near trees.
Watering of lawns is beneficial to trees if the watering is done correctly. Trees need the equivalent of one inch of rain every seven to ten days. Frequent, shallow watering does not properly meet the needs of either trees or turf and can be harmful to both.
Turf growing under or near trees should be mowed at the top of its recommended mowing height. Mowing off no more than one-third of the grass blade's height and letting the clippings remain on the lawn will do much to ensure a healthy and vigorous lawn. In an ideal situation, tree and turf maintenance would be handled by the same individual in order to maximize the benefits of all maintenance practices.
Developed by the International Society of Arboriculture (ISA), a non-profit organization supporting tree care research around the world and dedicated to the care and preservation of shade and ornamental trees. For further information, contact: ISA, P.O. Box 3129, Champaign, IL 61826-3129, USA.
© 1995 International Society
UPDATED FEBRUARY 2000