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
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
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 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.
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.
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
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.
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.
from the University of Massachusetts Extension, 2000