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University
of Rhode Island GreenShare Factsheets
Ornamental
Grasses
Ornamental grasses haven't been so popular
since the Victorian Age. Dozens of ornamental grasses are now
available, and new forms are being added each year. The reasons
for this astonishing rise in popularity appear to center around
the practical, as well as the aesthetic merits of ornamental
grasses. As the public becomes more environmentally aware,
and learns more about low maintenance plants and sustainable
landscapes, ornamental grasses that can tolerate extremes of
drought and wetness are eagerly sought. Many ornamental grasses
are also able to endure the repeated soil freezing and thawing
typical of northeastern winters. Ornamental grasses are also
a part of the growing popularity of water gardening, as transitional
elements between dry land and water.
Ornamental grasses serve many functions
in the landscape. Ornamental grass foliage catches the wind,
adding a sense of
motion to the landscape. The native prairies of the Midwest
were often described as an inland sea. Tall grasses also rustle
in the wind, adding sound as a new dimension to the landscape.
In a border, grasses can be used as edging or background plants,
while larger specimens can be accent plants or screens. Rhizome-
and stolon-forming grasses stabilize banks or serve as ground
cover. Diminutive species can be utilized in rock gardens.
Combining grasses with woody or herbaceous perennial plants,
such as
shrub roses or Sedum 'Autumn Joy', help create a beautiful
and enduring, low input, sustainable landscape. The dried foliage
and flowers of many ornamental grasses are attractive and sway
with the wind thoughout the cold winter months. Many are excellent
for use in floral arrangements.
Ornamental grasses, in both foliage and inflorescence
(seed head), vary greatly in size, shape, color and texture.
One of the largest ornamental grass collections in the Northeast
may be viewed at the University of Rhode Island East Farm Agricultural
Experiment Station in Kingston. Call (401) 874-5220 to schedule
a visit. Mature plants range in height from 6 inches (blue
sedge, Carex glauca) to 14+ feet (hardy pampas, Saccharum
ravennae). Grass forms vary from low mounding to fountain
shaped to tall vertical. Foliage color includes shades of green,
yellow, blue, red, brown and variegated (green and white mixed).
A number of grasses change in foliage color in the fall, to
displays of straw yellow, orange, red or purple, providing
a wealth of choices. Foliage texture varies from fine to coarse
(blade width from 1/8 to 1 inch). The inflorescence also varies
in size and color, and may change color in the fall as well.
Although a few grasses tolerate shade, most require full
sun. Some grasses or grasslike plants tolerate wet soils, but
more require a well-drained soil. To become drought and pest
resistant, plants require a suitable root zone. In compacted
soils, even the root systems of the most drought-tolerant plants
will not develop. Incorporate organic matter into the root
zone to improve water-holding capacity and oxygen levels. Adequate
organic matter will develop a soil with sufficient pore size
to readily release water. The improved root zone will allow
for maximum root expansion and water extraction from the soil.
Improving the soil also will reduce irrigation frequency. Your
investment in soil improvement will be returned in fewer maintenance
problems and more attractive, longer-lived plants.
Ornamental grasses may be propagated from seed or division,
and can be purchased from seed companies, mail-order firms
and garden centers. Generally, the improved strains, which
include most of the new varieties, will not come true from
seed and must be propagated from divisions. Many grasses do
not transplant or propagate well after midsummer because root
growth slows dramatically. Container-grown plants may be transplanted
into the landscape throughout the growing season.
Since the foliage portion of the plant should be cut down
to the ground and removed each fall or spring, some fertilization
is required to compensate for nutrient loss. A 10-10-10 fertilizer
may be applied at a rate of 1 pound per 100 square feet. A
good deal of calcium and magnesium is lost when removing foliage,
therefore a soil test for deficiencies of these elements should
be carried out periodically and recommendations followed. Do
not over-fertilize ornamental grasses, as this can lead to
lodging (falling over) and disease problems.
In contrast to other flowering perennials, ornamental
grasses require minimum maintenance and most species are both
insect and disease resistant. However, improperly sited plants
may become diseased because of poor air movement, high nitrogen
soils or inadequate light. As ornamental grasses becomes more
common, pest problems may develop. At that point, cultivar
selection will be more important.
As with most plants, there are common myths or misunderstandings
about the ornamental grasses. For example, many durable and
hardy ornamental grasses growing in Rhode Island are mistakenly
called Pampas grass. Cortaderia selloana, the only true
Pampas grass, will not grow in Rhode Island. Ordering grasses
under the name of Pampas grass will result in disappointment
in this region.
Planting grasses whose dried foliage is to remain for
the winter near combustibles such as a house or garage is not
a wise practice. Dry grass foliage and flowers can be highly
flammable. Remove foliage in the fall if a potential fire hazard
is at all possible.
The first question to ask about a grass: is it rhizomatous
(spreading by underground stems) or clump forming? Rhizomatous
types make excellent ground covers, erosion control plants,
and dense cover plantings that resist the invasion of weeds.
The rhizomatous types spread at different rates laterally,
some as much as twelve or more feet a year, and may be invasive.
The clump formers simply increase in circumference, requiring
division every three or four years. Distinguishing between
the two types and locating them in proper sites will prevent
a great deal of difficulties in managing the garden, and results
in great satisfaction from this very desirable group of plants.
There are many grass or grasslike plants
suitable as ornamentals, both native (ex. big bluestem, Andropogon
gerardii) and exotic (ex. fountaingrass, Pennisetum
alopecuroides 'Hameln'). Native grasses were members of
the local flora before European settlers arrived. Exotic grasses
are introduced plants from other states or countries. Some
have escaped cultivation and become part of the local flora.
Some grasses, such as little bluestem, annual pennisetums,
and early flowering Miscanthus, can reseed in your garden or
spread to wetland areas where they can become real pests. New
grass species and cultivars should be evaluated for invasiveness
before being grown for sale.
The most popular groups of ornamental grasses
are Festuca (fescue), Miscanthus, Panicum (switchgrass) and
Pennisetum (fountaingrass).
Fescue: This cool season, clump-forming
grass requires protection from the hot afternoon sun. Blue
foliage forms are the most popular. Division in the early spring
is often required to restore vigor. Regular fertilization may
benefit this group.
Miscanthus: Considered the showiest
group of warm season, clump-forming grasses, it has very showy
flowers. A large group of grasses with considerable variability
in height, blade width, etc. Select cultivars carefully to
insure adequate hardiness and adaptation to your site.
Switchgrass: This native, warm-season,
clump-forming group is becoming more popular as new cultivars
become available. Cultivars with red fall color and blue foliaged
upright cultivars are popular.
Fountaingrass: Most members are warm
season, clump forming grasses. Some may become weedy, especially
south of Rhode Island. Both annual and perennial cultivars
are valuable in the landscape. Flowers are showy and are foxtail-like
in their appearance.
Dr. Brian Maynard, Sustainable
Landscapes Program Department of Plant Sciences, URI, Kingston,
RI
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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