Thursday, June 30, 2011

Native Grasses & Natural Landscapes

The introduction of ornamental grasses to the American landscape is one of the defining moments in modern garden design. These grasses, planted in clumps or large masses, recall elements of the nation's vanishing prairie, while adding sophistication and panache to even the most groomed garden.

Regrettably, many of the grasses frequently used, especially those with ostrich feather-like plumes or stylish zebra-stripes, are both exotic and invasive, especially when planted near open fields, and can pose serious problems for our local ecosystem. For a more habitat-friendly approach, gardeners can and should turn to the abundant inventory of native grasses which will provide the same elements of year-round color, texture, and graceful, swaying motion.

One of the most widely available and popularly used native grasses is big bluestem (Andropogon gerardi), or "turkey foot," affectionately dubbed "monarch of the prairie" by some horticultural boosters. Big bluestem was the dominant species of grass which formed our fabled tall grass prairies, as well as the sod used by homesteaders (sodbusters) and pioneers to build sod huts.

Sod dwellings don't show up very much in most parts of the country, but big bluestem does, both in habitat restoration plantings and in backyards, where they are frequently clumped in mulched planting beds or "grass islands" which decoratively float atop a trimmed lawn. Formal plantings also use these seemingly untamed specimens to dramatically frame a front entrance or serve as sentinels at the end of a driveway.

Big bluestem can reach up to ten feet in height and prefers full sun, although it is tolerant of partial shade and either moist heavy, or sandy, drier soils. Like most native grasses, it prefers being left alone, and fertilizing or unnecessary watering will simply lead to floppy growth. This is a tough plant, let it prove itself! The plant's common name comes honestly from its vertical height and the subtle blue tint of the stem. And while the leaves remain bluish-green during much of the year, autumn frosts help transform that foliage to a mellow bronze or copper shade which will last throughout the winter.

The plant's less common name originates with the three-fingered prongs or "rames" of the purplish-blue seed head, which resembles a turkey's foot, and which begin forming in late summer, and provide seed to a host of migratory and native songbirds through early winter.

A close cousin to big bluestem is little bluestem (Schizachyrium scoparium), which shares many of its relation's best characteristics, although it is best planted in masses for best effect, especially considering the beauty of watching a whole miniature sea of grass swaying their silver seed heads in the breeze.

Also a sun lover, the fluffy, tufts of this species mature on a clump-forming plant destined to stay between two and three feet in height. Like most sod-forming grasses, little bluestem does most of its growing underground, sending roots eight feet deep, which makes it equally adaptable to periods of drought or flooding. These qualities make it ideal for erosion control and mower-free hillside stabilization. It is also salt-tolerant, which nominates it for use as en edging plant along sidewalks and curbs.

For gardeners looking for a mid-size grass, there are few more noteworthy than switchgrass (Panicum virgatum), a full sun plant that can adapt to partial shade and either moist or dry conditions. It is wonderfully useful as either a specimen plant, or in small, bush-like clusters, or even planted en masse. Maryland-based garden writer Carole Ottesen favorably compares these massed plantings to a field of wheat. Staying somewhat between three and eight feet tall, depending on soil conditions, the rich green foliage slowly takes on a buttery-cream complexion in fall.

Another attractive and adaptable option for yards with light to moderate shade is bottlebrush grass (Hystrix patula). This species is modest in most respects, averaging only two to five feet in height, and producing only moderately attractive, medium-green foliage, turning straw-colored in autumn. However, the bristly seed heads are quite remarkable, resembling by turns an actual bottlebrush or the long quills of a hedgehog, from which the genus name Hystrix (porcupine) is taken.

And while almost all grass seed heads make for wonderful dried or cut flower arrangements, bottlebrush flowers are incomparable when placed in a window for a striking bit of backlighting.

A close rival for flower arranging - and garden use - is northern sea oats, or river oats (Uniola latifolia), a low-growing, shade-tolerant species whose 30 inch height makes for an excellent ground cover or placed along a perennial boarder, where visitors can fully appreciate its drooping clusters of oat-shaped seeds and rusty-orange fall foliage.

In the same vein, broom sedge (Andropogon virginicus), another cousin of the bluestems, works well as a ground cover or for erosion control, with bluish-green clumps keeping to about 20 to 30 inches in height, with another foot or two more for its inflorescence. Like many of our favorite native grasses, autumn brings on a rich orange color, with seeds for meadow birds and the occasional migrant.

Clearly, the range and application of native grasses is limited only by the size of the garden bed or landscape, and its desired use. Taller and medium sized grasses can serve as hedges or screens, to hide unattractive fences or foundations, or more properly as a backdrop for other garden plantings. Typically, these individuals are best spaced two to three feet apart.

Medium to low-growing specimens often work best in larger groupings, planted one to two feet apart, and are used successfully as ground covers, especially those shade-loving or shade-tolerant grasses which can fill in nicely under mature trees with open scaffolding or along the edge of a wooded area.

A key to making the most of native ornamental grasses is combining them with other flowering natives, or non-invasive annuals and perennials, which will compliment the structure and form of the grasses, while providing color during the spring and summer, as well as a low-flowing, spreading appearance.

Lastly, to truly transform your grass islands or prairie shrubbery into an outdoor bouquet, try to marry the bronze, orange, and copper hues of fall foliage, to say nothing of their crimson-purple flowers and rusty-brown seed heads, with the floral display of late-summer and autumn show-offs like joe-pye weed, sunflowers, asters, ironweed, and goldenrods.

With any luck, the memory of your grassy garden, along with vases filled with bold sprays of seed heads, will keep you smiling all winter long.

Copyright 2011, Joseph M. Keyser

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