Kentucky Bluegrass Lawns
Although most Kentucky bluegrass varieties prefer sun, there
are some that tolerate shade, such as Bristol, Eclipse, Georgetown,
Glade, Midnight and Sydsport. The best shade mixtures are roughly 60
percent fine fescue and 40 percent shade-tolerant Kentucky bluegrass
There are other steps to help your shady lawn. It is helpful
to limb up the trees a little and have the canopies thinned to allow
more sunlight through. You should hire a certified arborist to prune
large trees. They have the training and equipment to do the job
correctly and safely.
Besides casting shade, established trees compete with the
turfgrass for water and nutrients. This might not be a problem for
you because you have moss, indicating that excessive moisture may be
more of an issue. In most other cases, water deeply once or twice a
week when there is no rain, applying at least an inch of water at a
time. This means setting up your sprinkler to apply about a
half-inch of water an hour because that is what our clay soils are
able to absorb without runoff. If the area is sloped, you may have
to apply the water more slowly to avoid runoff.
You should also fertilize shaded turf at a slightly higher
rate than you would otherwise. Although you should start with a soil
test, using a slightly higher rate of nitrogen will benefit the
Fine fescues ordinarily require 1 to 2 pounds of nitrogen per 1,000
square feet over the growing season. To make up for the competition
from the trees, 2 to 2-1/2 pounds of nitrogen per 1,000 square feet
should be sufficient. This should be split into at least two
applications in late spring (mid-May) and late fall (mid-November).
If you prefer three, divide the nitrogen into three applications,
adding one in late summer (early to mid-September). Turf-type tall
fescue ordinarily takes 2 to 3 pounds of nitrogen over the growing
season. To compete with trees, raise that to 3 to 31/2 pounds.
Rough bluegrass and Kentucky bluegrass prefer 3 to 4 pounds of
nitrogen per season. Under trees, use the 4-pound rate. Use the same
timing suggested above.
To calculate how many pounds of fertilizer you need, divide 1
pound by the percentage of nitrogen in the fertilizer. For example,
how many pounds of 32-3-5 fertilizer are required to apply 1 pound
of nitrogen per 1,000 square feet to a 5,000-square-foot lawn?
Thirty-two percent is the amount of nitrogen, 3 percent is the
amount of phosphate, and 5 percent is the amount of potash. These
nutrients are always listed on a fertilizer bag in the same order.
1 ÷ .32 = 3 pounds
Multiply the 3 pounds by 5 to find that it takes 15 pounds of 32-3-5
for a 5,000-square-foot lawn. Simply substitute the analysis of the
turf fertilizer you normally use and the size of your lawn to
calculate how much is required to apply the suggested amount of
IMPORTANT: Proper Mowing
It is also important to maintain a higher cutting height when
turfgrass. There is a directly proportional relationship between the
topgrowth of the grass and the depth of its root system. The shorter
you cut it, the less root system it has to compete with the trees.
Leaving the grass longer also shades out germinating weed seeds. (It
is important to control weeds on shaded turf to eliminate their
competition for water and nutrients. The fact that turf in shaded
areas is often thin creates an ideal opening for weeds to creep in.)
Finally, keep falling leaves
off the grass as they block out the sun and starve
the roots by interfering with photosynthesis. This weakens the grass
plants and makes them more susceptible to other stresses because
they cannot manufacture sufficient energy reserves.
There are a number of factors that create an ideal environment
for moss: moisture, shade, soil compaction (because it reduces
drainage), low soil pH and low soil fertility. Excessive moisture is
the most important factor. Moss will grow in full sun and alkaline
soil as long as there is moisture.
Hiring an arborist to thin the crowns and limb up the trees will
allow more sun to reach the ground and speed drying after it rains.
followed by a thin top dressing of compost -- one-eighth to
one-quarter inch -- will help alleviate soil compaction and improve
drainage. You can have the
soil tested and
apply lime and fertilizer to favor the growth of grass.
OR ... you might want to consider working with what you have and not
struggling to grow grass in an environment that does not naturally
support its growth very well. You might create lightly mulched beds
under the trees -- perhaps you can encompass groups of them in a
single bed and underplant them with shade-tolerant shrubs and
perennial plants such as ferns, hellebores and native bleeding heart
plants. And dare I suggest ... moss?
In place of grass...
When you plant shrubs and perennials under trees, do not work up the
whole area; just dig holes twice the size of the rootballs and plant
Arrange for the mulch to extend out from the trees the length of
their limbs (known as the drip line). Two inches of mulch is all
that is necessary. You can place it close to but not touching the
bases of the tree trunks. Trees and grass have many opposing needs.
Grass prefers a higher fertility level and more neutral
soil pH than many
native trees. Changing the soil chemistry to favor grass will spell
trouble for the trees over time.
Test your Soil
Penn State soil test kits are available for $12 each. If you
purchase more than one kit at a time, additional kits are $9 each.
Make checks payable to Penn State Cooperative Extension and indicate
the number of kits you want. Send to Soil Test Kits, Penn State
Cooperative Extension, 400 N. Lexington St., Pittsburgh 15208.
Fall foliage tour
Trees and Shrubs for