Prepared for the Calgary Horticultural
ORNAMENTAL PERENNIAL GRASSES
In our short (or
“mixed”) grass prairie ornamental grasses are in an ideal environment to
provide highlights in our gardens and to compliment other perennials. Calgary
has been in the grassland biome for millennia, in part because grasses’
survival techniques include the presence of growth zones in the sheath at the
base of each blade which protects them from grazing and from fires. Our gardens
are typically described as being within zone 2b or 3, but grasses are often
cautiously labelled in older texts as belonging to zones 4 or 5, yet grow
belong to the monocot Poaceae (or Graminaceae) families, and about fifty
varieties of these can grow here. Most mature within three years and with
adequate water the majority are suitable for well-drained sunny sites but there
are at least a dozen that tolerate shady or moist sites quite well. In the last
century in Calgary, grasses were considered unattractive because of their
invasive rhizomes or stolons. One problem may have been that our season was not
long enough for some grass seeds to germinate and mature. In contrast to those
invasive grasses, “clumping” grasses have become increasingly popular,
especially over the last five to ten years throughout N. America, where
nurseries now offer a variety of grasses and grass-like plants.
When looking for
perennial grasses, keep several criteria in mind. Foliage colour varies, and
some are striped vertically, others horizontally. One of the attractive features
of grasses is that they provide year-round interest, and should be positioned
accordingly. The taller ones need enough room to permit them to “strut their
stuff” so they need as much space as their height: shorter ones can provide
interest to the front of borders. Their form varies; some are upright, such as
the Feather Reed grasses, others such as Blue Oat grass, are arching. Contrast
these with the short, mounded grasses like the fescues. In detail there are
combinations of those forms as well as “tufted” varieties. Note that the
heads often remain all winter, and their variable forms provide interest when
dormant, with racemes in the invasive Ribbon Grass, panicles in Tufted Hair
grass, and spikes as in the annual Purple Fountain Grass.
The stems or
culms lead to groups of flowers that produce wind-borne pollen. One interesting
feature of grasses is that the flower groups, or inflorescences, can rise to
twice the height of the foliage and the height to stem width ratio of grasses is
characteristically high, (in wheat, which belongs to the grass family, it is
100:1). Look for foliage and flower height in good texts such as “Grass
Scapes” by Quinn & Macleod.
season/warm season categorization of grasses, based on the temperatures needed
for rapid growth, is useful in the warmer parts of Canada and in the USA but has
less importance in Calgary unless we continue to have longer fall conditions.
Cool season grasses green up earlier and slow down or stop growing at
temperatures above 24o C (75 o F), but have the advantage
that they may retain their colour into fall and deeper into winter than the warm
season grasses, and may green up earlier in the spring. However, the warm-season
upright, grass, Japanese Blood Grass, Imperata cylindrica var. koenigii
‘Red Baron’, with its very attractive bright crimson colour can be grown
here as an annual to give fall and early winter colour and it forms a superb
contrast in colour against taller grasses with green foliage. Miscanthus
varieties can also be grown here as annuals for fall colour.
Most grasses here
grow well in our alkaline soil, but some, Tufted Hair Grass and Bulbous Oat
Grass, for instance, prefer acidic soil. The life-expectancy of grasses is
variable; Pampas grass, which rarely will flower here, can be over a
hundred year old yet some fescues may only last three years. The fungus, rust,
is the only common disease in grasses and it is not fatal, Bulbous Oat Grass is
susceptible to rust, as is Blue Oat Grass if the latter is in too much shade.
Grasses need little maintenance, but should be watered well in the first and
possibly second spring: in less fertile, drier, soil they are slow to grow.
Invasive types can be controlled that way, or put in open-ended pails. In terms
of maintenance, a spring haircut is good: a rule of thumb is that for plants
greater than 1.0 m high trim to 10cm, and for smaller plants, cut back to 5cm:
the small fescues need simply a brushing to remove the old blades in the spring.
Division can best be done then too.
hardy, attractive year round colour, appealing and varied foliage, form, and
fascinating flower heads. They provide graceful movement and sound, and add
humus content, trap snow, retain water and some control erosion. Careful
placement provides contrast to other plantings especially if combined with
broad-leaved perennials and they can be focal points or provide background. If
used selectively, they can be partnered with one another. From the colour
perspective, the tougher varieties retain their blue or green foliage well into
winter, while their tall seed heads turn golden brown.
Keep in mind that
heights (too high) and zones (too pessimistic) given in texts and on the web can
be quite wrong. Zone definitions in the US based solely on minimum temperatures
differ from Canadian ones. Colours and names can be misleading too, and synonyms
abound: For good design ideas, turn to Kurt Bluemel (http://www.kurtbluemel.com),
Karl Foerster, Wolfgang Oehme, Piet Oudolf, or Jim Van Sweden.
* This article
does not examine the sedges, rushes, cattails or restios, but these and several
annual grasses can provide similar effects in our gardens especially in moister
Recommended Ornamental Perennial Grasses
Horticultural Society. The Calgary Gardener. 1995. Canada
Rick, The Colour Encyclopedia of Ornamental Grasses, 1999. USA
June, Native Plants for Prairie Gardens, 2005, Canada
J., The Encyclopedia of Ornamental Grasses, 1992. USA
Roger, Gardening with Ornamental Grasses, 2004, UK
M., Ornamental Grasses for Cold Climates, 2004. USA
Kam, B., and
Bryan, N. The Prairie Winterscape, 2003. Canada
M., and Oudolf, P., Gardening with Grasses. 1998. Europe
N.J., Grasses, 2002. USA
M., and Macleod, C., Grass Scapes, gardening with ornamental grasses, 2003.
B., Native Grasses in the Landscape, 2005, Canada
Nov 14, 2005.doc