June 1, 2011
By Sue Dyer
Ornamental grasses are some of the most underrated and under-used categories of plant material in modern landscaping. Their reputation is growing, but with so many advantages and so few disadvantages, it is clear their popularity has yet to peak. Given the impact, versatility and benefits these plants can offer, landscapers would be well served to consider them when planning their next project.
The changing seasonal nature of ornamental grasses provides four-season interest. In spring, they tend to ‘wake up’ relatively early, at the very least producing green foliage. Early-blooming varieties will provide intricate and interesting blooms, often much taller than their foliage, while late bloomers provide engaging foliage colours, giving great contrast with early bloomers in mixed plantings. As the late bloomers begin to flower, the flowers on the early bloomers will change colour, while the stems will transition to a beige or wheat-coloured shade.
From a size standpoint, large specimen grasses can be a great alternative to trees, in large part because they can often reach impressive heights much faster. For instance, northern pampas grass (Erianthus Ravennae) will grow plumes of 3.6 m (12 ft) during a single growing season. Tall plumes, if left intact, can also provide attractive winter interest. Plumes and blooms tend to be cut in the spring, before new growth comes in, allowing plants to remain interesting during the dead of winter.
Cultivating areas of group plantings in drifts can also create added impact. The density of the plantings and motion created as the wind causes grasses to move and sway en masse can make an immense visual effect. European marram grass (Ammophila arenaria, also know as European bench grass) is a good example of this, as is the popular miscanthus.
In addition, ornamental grasses can be used to soften any large or somewhat unattractive objects, such as buildings, industrial venting units or large air conditioners, while lower-growing varieties can be used as effective ground covers. There is also a wide range of colours available, from traditional greens to brilliant blues (e.g. Elijah blue fescue [Festuca glauca] or blue wheatgrass [Elymus Magellenicus]) to yellows, purples and reds.
An extensive range of ornamental grasses are currently available on the market, making it easy for landscapers to find the right variety for specific conditions, such as hot and dry settings, wet areas, shady or partial shade areas, container growing or large expanses. For example, one might choose a blue fescue for dry borders and june grass (Koeleria) for dry, prairie-like conditions, but opt for Glyceria Maxima, known as reed sweetgrass or reed mannagrass, for wet-edged settings and cat tails (Typha Latifolia) for very wet conditions.
While versatility abounds, it should be noted that ornamental grasses do have their limitations. For example, many a landscaper has planted pampas grass in a northern climate and failed to survive, as most varieties are not hardy to cold regions. (That said, some varieties not suited to colder climates perform quite well when planted in sheltered areas.)
Also, many varieties promoted in magazines and other publications simply won’t survive outside of a warm climate. Nevertheless, such publications continue to promote spectacular specimens, without the caveat of climate suitability.
It is therefore critical to be aware of local plant zone designations to ensure any grasses chosen are compatible with the area. For example, Carex is a very popular landscaping species, but it often does not survive in northern regions. There are, however, varieties that thrive in colder climates, such as Carex Nigra, which offers dramatic black blooms that can be used quite effectively in landscape designs.
Ornamental grasses are also largely unaffected by diseases and pests, resulting in better survivability, improved and consistent appearance, low pest control costs and reduced maintenance budgets. Their deep and fibrous root systems discourage gophers and other tunnelling animals. Grasses also improve soil conditions and fertility, even without supplemental feeding and can provide seeds for birds and other wildlife.
In addition, ornamental grasses can be used to create buffer zones for water features. In many cases, constructed wetlands have used large areas of reeds as small-scale sewage treatment systems. This demonstrates the significant filtration benefits of many grasses, which has subsequently led to the extensive use of grasses in swimming ponds. The right blend of grasses can produce a clean and safe environment in which to swim, without the need for chemicals and labour-intensive manual cleaning. The result is a visually attractive water feature that rivals a swimming pool, with significant environmental and health benefits.
Further, ornamental grasses can be used to stabilize slopes and waterfronts because their often extremely dense root systems are able to hold large masses of soil in place. In terms of shape, their upright form tends not to take up as much space as most shrubs, trees or more traditional perennials. Mixed with broadleaf annuals or perennials, they can add stunning texture, colour and size, whether large or small.
Ornamental grasses are low-maintenance plants, requiring only a spring cut-back. It is best to cut off blooms in early spring and cut the entire plant down to a height of approximately 80 to 100 mm (3 to 4 in.). This allows substantial new growth at a time when the plant will not be harmed from being cut, while ensuring the old, unattractive foliage and blooms from the previous year do not get mixed in with the new growth. While cutting blooms or foliage in the fall will not necessarily kill the plant, it can cause long-term damage and is therefore not recommended.
Ornamental grasses also have very low nutrient requirements. In fact, some become less healthy as soil nutrient conditions improve. (The aforementioned northern pampas grass is one such example.) They require little, if any, fertilization and are largely unaffected by poor weed control. Also, very few species are invasive in Canada. The varieties that do spread need not be avoided; instead, they should be planted selectively. Choose areas in which a substantial amount of the same grass species will be visually attractive and where the spreading nature of the plant will not cause issues with neighbouring plant material.
Most ornamental grasses are ‘clumpers,’ meaning as they grow in height, they will also grow in breadth. If left too many years, their breadth will expand such that the centre of the plant will begin to die out. At this stage (or before), the plant can be dug in the spring, divided rather aggressively into three or four plants and replanted. This, effectively, is how they reproduce. Many natural grass species spread by seed, causing them to be incorrectly labelled as invasive or simply undesirable. However, where this is the case, a perfectly suitable cultivar without the same spreading tendencies can usually be found.
The few compromises and disadvantages associated with ornamental grasses make them a visually interesting, versatile and beneficial option in any landscape design. Armed with the right knowledge, landscapers will no doubt continue to incorporate these unique plants into their designs.
Sue Dyer is the owner of Kings Creek Nurseries in Ashton, Ont., near Ottawa. She can be reached via e-mail at email@example.com.
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