In order to grow turf under shaded or partially shaded conditions, it is necessary to understand both the detrimental effects of shade as well as cultural practices which can be used to minimize these difficulties.

Reduction of Light:

Although buildings and other structures may shade turf, trees are generally the most common cause of shade. The most obvious impact of shade is a reduction in the amount of light available to the turf. Grasses, like all green plants, convert light energy into carbohydrates via photosynthesis. These carbohydrates serve as the building blocks and energy source for plant growth and development. Thus, if a plant does not receive enough sunlight to manufacture sufficient "food" (carbohydrates), its vigor and growth will be reduced. In addition to reducing the total amount of light available, tree shade also severely limits the amount of useful light reaching the turf. All wavelengths of light are not equally effective in photosynthesis. Green plants absorb (and use for carbohydrate production) primarily orange, red and blue light, while they reflect mainly green and yellow (which are not very effective in photosynthesis). Therefore, the majority of light reaching shaded turf is likely to be light which has filtered through the tree canopy and is low in the wavelengths most valuable in photosynthesis and carbohydrate production.

Root Competition:

Aside from altering the light reaching the turf, some trees produce surface roots which compete with the grass for nutrients and water. This competition further inhibits the ability of the grass to grow, and it becomes very difficult to maintain a turf of desirable quality. Exclusion of rainfall by tree canopies can dispose shaded turf to drought stress, a situation which is often overlooked when assessing shade effects. Increased relative humidity and decreased air circulation in wooded areas favor development of turfgrass diseases such as powdery mildew, as well as encouraging moss and algae problems.

Tree Management:

Intelligent tree management practices are essential to any effort to minimize shade problems for turf. Decline of turf growing under trees may occur gradually over a number of years. As trees grow, their canopies become wider, thicker and denser, and their roots increase in mass and spread. Consider removing trees and shrubs which do not contribute meaningfully to the landscape design. Pruning tree limbs which grow at heights below eight to ten feet can often substantially improve the amount of morning and afternoon sunlight reaching the turf. Selective thinning of the tree canopy itself will also allow more photosynthetically useful light to penetrate to the turf. Planting of shallow-rooted trees such as willow, silver maple, cottonwood and sweetgum should be avoided, if possible, in order to reduce nutrient and water deficits due to root competition and to avoid future impediments to mowing.

A program of tree fertilization can be initiated to provide for the tree's requirements, reducing the tree's competition with the turf for available nutrients.

Tree management practices such as pruning, thinning and fertilization can be harmful to a tree if carried out improperly. Consultation with a certified arborist is advisable before undertaking work on valuable trees.

Shade-Tolerant Turfgrasses:

When establishing turf under shaded conditions, species and cultivars possessing good shade tolerance should be chosen. The fine-leaved fescues (hard fescue, Chewings fescue and creeping red fescue), as a group, are generally well-adapted to shaded conditions. Although widely used throughout the northeastern U.S., only a limited number of Kentucky bluegrass cultivars possess adequate shade tolerance to provide a quality turf under shade. Tolerant cultivars include 'Bensun' ('A-34'), 'Birka,' 'Bristol,' 'Eclipse,' 'Glade,' 'Nugget' and 'Touchdown.' Rough bluegrass, Poa trivialis, is quite tolerant of shade, but its use is limited to moist, fertile soils not subjected to heat, drought or traffic.

Turfgrass Management Practices:

In order to provide increased leaf tissue for photosynthesis, mowing height should be maintained as high as practical in shaded areas (2.5-3.5 inches). Timely removal of fallen tree leaves and grass clippings also improves the supply of sunlight to the turf. Nitrogen fertilization is usually reduced to 1-2 lb. N/1000 square feet in shade (as compared to turf grown in full sun) in order to avoid stimulating growth that further reduces the plant's carbohydrate levels. Watering should be practiced infrequently (usually no more than once per week) to minimize disease potential. Infrequent, deep watering (to a depth of 6 inches) is desirable to encourage deep rooting of the turf.

Adapted from the University of Massachusetts Extension, 2000