Prepared for the Calgary Horticultural Society

ORNAMENTAL PERENNIAL GRASSES

The Calgary Scene

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 happily here.

True grasses* 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.

The cool 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 24^o 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.

Grasses provide 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 sites.

                Recommended Ornamental Perennial Grasses

Selected References

Calgary Horticultural Society. The Calgary Gardener. 1995. Canada

Darke, Rick, The Colour Encyclopedia of Ornamental Grasses, 1999. USA

Flanagan, June, Native Plants for Prairie Gardens, 2005, Canada

Greenlee, J., The Encyclopedia of Ornamental Grasses, 1992. USA

Grounds, Roger, Gardening with Ornamental Grasses, 2004, UK

Hockenbury Meyer, M., Ornamental Grasses for Cold Climates, 2004. USA

Kam, B., and Bryan, N. The Prairie Winterscape, 2003. Canada

King, M., and Oudolf, P., Gardening with Grasses. 1998. Europe

Ondra, N.J., Grasses, 2002. USA

Quinn, M., and Macleod, C., Grass Scapes, gardening with ornamental grasses, 2003. Canada

West, B., Native Grasses in the Landscape, 2005, Canada

Glynn Wright                          Nov 14, 2005.doc