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University
of Rhode Island GreenShare Factsheets
Growing
Turf under Shaded Conditions
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.
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.
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.
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.
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.
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
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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