Native Grasses

Native Grasses

By: Susan Tracy

Incorporating ornamental grasses into the planned landscape is a fairly trendy topic, judging from the number of recent articles in landscape design magazines and books newly published on the subject. It is easy enough to understand why.

What a range of choices this family of foliage plants offers the adventurous gardener-shape, size, texture, color, yearlong interest. Some tall species are dramatic enough, standing alone, to create a bold focal point; others form a dense hedge. Low clump grasses, massed, make an unusual groundcover. Spiky clumping grasses mixed with perennials in a border contribute to a relaxed, naturalistic look. In transition areas, massed swaths of waving grasses can blur the boundary between a formal garden and the natural landscape beyond. But why use the standard exotics like miscanthus, pampas grass, and fountain grass? Why not look closer to home for inspiration?

NATURE’S LANDSCAPE

For the past several years, I have been exploring the decorative potential of the perennial clump grasses native to my area-Bandera County ranchland, at the southeastern edge of the Hill Country. This interest evolved as I started planning the landscape to surround my new home, some six years ago. I envisioned a garden that would be a distilled, formalized reflection of the view beyond. With this goal in mind, I was determined to use only plants specifically native to my region. I made a decision, at the outset, to avoid irrigation as a means of artificially prolonging bloom and lush growth, instead choosing to follow nature’s lead-typically months of drought punctuated by infrequent, unpredictable and sometimes torrential rains. Since many of our flowering plants go dormant during the normally dry summers, color was clearly to be subordinated to other elements of garden design. Native clump grasses would be appropriate to the setting, I believed. How better to anchor a native garden to its setting? Mid- and tall-prairie grasses were once a characteristic feature of this region, after all. In the wild, they are easily established, quick to mature, and, absent overgrazing by livestock, long-lived. Our native grasses, deep-rooted, are extremely drought-tolerant. Best of all, this family of plants is one of the few unpalatable to deer, a major problem in my area! And still I was warned off from grasses, as too aggressive, and too unruly, and too messy. In a word, “garden thugs.” Happily, I was able to work with inspired landscape architect Rosa Finsley, from Dallas, who understood my vision, and guided my hand in the garden’s design and initial installation. In the years since, I have been impressed with how well many of the native clump grasses we incorporated have performed, in many cases surpassing the effect I hoped for. Learning the characteristics of each, over time, I know better now what will work out, what won’t, and why-principles which I encourage gardeners from other areas to apply to their own native species.

Most importantly, I want to know how a grass will look in every season. Garden book photos often feature what I call close-up “plant portraits,” highlighting a grass’s flower clusters (its ‘inflorescence’) but ignoring its seasonal vegetative characteristics. Most of our clump grasses exhibit significant foliar changes from season to season. Some grow most actively early in the year; others do not mature till later. The second group, termed “warm-season” grasses, put out vigorous new growth during late spring and on through summer, climaxing with seed formation in early autumn. Their foliage dries once they go dormant, in early winter, and new growth does not emerge until the following spring With these late-season grasses, an area full to overflowing in late summer can present a near-void after the dead growth is finally cut back, a maintenance chore best completed just as the new shoots start to emerge. By the end of spring, however, warm-season grasses are again growing actively, and continue to develop through summer.

WARM SEASON GRASSES

Indiangrass, little bluestem, switchgrass and big bluestem, four dominant species of the tall-grass prairies, are all warm-season grasses. All are highly drought-tolerant. Of them, my personal favorite is Indiangrass Sorghastrum nutans, its pale-bluish foliage crowned with dramatic gold inflorescence in late summer. In winter, the foliage dries to a peach-tinged buff color. Isolated but dense colonies of Indiangrass are occasionally to be found in nature, in full sun or light shade and in well-drained soil. As the growth pattern indicates, Indiangrass spreads mainly by rhizomes. For this reason, maintaining it as a solid swath is much easier than as distinct clumps. Plants set about 2 feet apart will merge together within two or three years. In my garden, this grass has been a star performer during the extremely dry summers we have been experiencing recently. Just as well, for excess water is said to make Indiangrass leggy and floppy, and encourages fungal problems when it is in flower.

For yearlong variation in form, it is hard to beat little bluestem Schizachyrium scoparium. In spring, its new growth makes a low clump with laxly arching, bluish-green foliage. In summer, when the stiff flowering stems appear, the plant shoots up, forming a tall, columnar mass now a deep olive-green. In autumn, the plant blooms. Back lit, it looks star-studded. Little bluestem maintains its upright form well into winter, the dry foliage turning a striking deep rust color. A loose grouping of nine to 10 plants interplanted with perennials, relatively inconspicuous in the spring, is far showier from midsummer on. Unlike Indiangrass, little bluestem is a slow grower. Since it does not spread by rhizomes, each plant, expanding very gradually, remains a distinct unit rather than merging into a solid mass.

Switchgrass Panicum virgatum is the tallest species I have used, well over 6 feet by summer’s end. Its feathery, pink-seeded plumy inflorescence is delicate and finely textured, yet almost insignificant relative to the sheer mass of the plant. A single specimen makes a handsome focal accent. Alternatively, spaced about 2 feet apart in two staggered rows, a group of switchgrass plants in my garden creates an informal, seasonal hedge, a dense barrier from early summer until I cut it back in late winter. Although switchgrass normally enjoys extra moisture in its preferred habitat along watercourses, it thrives in full sun and survives prolonged dry periods. In fact, this placement helps to limit a tendency to self-seed.

Big bluestem Andropogon gerardi, in spite of its name, is not. It is smaller than switchgrass, and until its characteristic “turkeyfoot” seedheads develop in the fall, not as tall as little bluestem. Sadly, this non-aggressive species is rare in nature now, so while it offers less visual drama than the other three, I included a small grouping in my entry-way to complete a symbolic connection with the region’s past.

Several species of muhly grass, native to my area, have great ornamental potential. Unlike most other late-season grasses, they look good in virtually every season.

Lindheimer muhly Muhlenbergia lindheimeri is the most familiar to landscape professionals, with good reason. This large (to over 4 feet when in bloom) grass stays green yearlong with little variation other than in autumn, immediately after its dramatically bold, spear-shaped inflorescence appears. Lindheimer muhly is non-aggressive, only expanding slowly outward. Over time, its center tends to die out, so periodically I will comb this grass through with a cultivator, pulling out any dead matter. One mature plant, or a small tight grouping, can provide an impressive focal point in the landscape. For a spikelike accent in a mixed border, the smaller (2 feet), more compact pine muhly M. dubia, may make a better choice. Except for its less impressive inflorescence, pine muhly is quite similar in appearance and growth habit to Lindheimer. On my property, this species grows naturally in full sun on my thin-soiled, rocky, flat hilltop, but it has adapted happily to the rich soil my garden provides. Seep muhly M. reverchonii is yet another in this genus with year-round decorative value, similar in appearance to gulf muhly. It is probably most effective when used in a mass planting for a groundcover, for both practical and aesthetic reasons. Its tendency to self-seed in suitable habitat tempers its welcome in a mixed planting, but planting it as a solid isolated mass accentuates the cloud-like effect of its delicate foliage, and, in early autumn, its elegant, smoky pink inflorescence. In nature, seep muhly is usually found near water, as its name implies. On my property a few small colonies of this grass can be seen along the river, growing in full sun. In my garden, it is planted in a bed only lightly shaded, yet it has turned out to be surprisingly drought-tolerant. A prolonged dry period does induce dormancy, however. When the rains return, I just cut the mounds down hard to encourage rapid new growth.

COOL SEASON GRASSES

By contrast to the grasses above, all late-season bloomers, “cool-season” species grow most actively during late winter and early spring, generally setting seed well before summer. In early spring, the lush green foliage of a cool-season grass seems particularly welcome, but it is important to factor into the garden design the characteristic appearance of the grass later in the season. Canada wildrye Elymus canadensis and Virginia wildrye E. virginicus, for example, are medium-tall cool-season grasses suitable for a dry, lightly shaded area, with bold flowering spikes appearing by mid-spring. The seedheads persist for many months, but by July the plant’s foliage tends to go dormant, with new growth not appearing till fall. The wildryes are best cut back to the ground at this point, or placed where dry summer foliage will not be discordant. I use them as casual, isolated accents at the wild edge of the garden, much as they might appear in nature.

Three-flower melic Melica nitens is another cool-season species also preferring part shade, but with a longer season of interest than wildrye. It is particularly beautiful while in flower in midspring, with a clustered profusion of showy spikelets. Its seeds disperse readily, however, and in suitable habitat volunteers soon proliferate, so I harvest the stalks when the seeds first ripen, scattering the laden stems around my property to promote germination away from the garden. Then, once the plants have finished blooming, I cut the foliage back severely, inducing fresh verdant clumps that will stay lushly green for the remainder of the growing season.

Inland oats Chasmanthium latifolium is another cool-season grass looking good year-round, with coloration varying from season to season. New growth emerges in late winter-a luxuriant, vibrant, pale yellowish-green, slowly turning dark bluish-green by summer. The plant flowers in spring: flat green spikelets nodding on laxly arched loose panicles. By late summer the seeds have ripened, their tan color a contrast to the foliage, which by now is a soft, olive-tinged green. Even after the leaves finally dry in early winter, the plant itself remains handsome. Its seeds are slow to break off, and its stiff, bamboo-like foliage rustles in the slightest breeze. I generally wait until late January, when the next year’s shoots break ground, to remove old growth.

One word of warning: inland oats is an aggressive self-seeder. In its natural habitat, the moist rich soil of shady streambeds, it forms extensive colonies. Clearly, self-seeding is an undesirable characteristic in a mixed border planting with regular irrigation. At the same time, inland oats is a most effective and unusual, elegant massed groundcover. I planted it in the shade of a live oak, in a rock-bordered bed with a sunny, dry pathway beyond. Volunteer seedlings within the bed are welcome, while the inhospitable habitat outside the border discourages germination.

Finally, sideoats grama Bouteloua curtipendula, the state grass of Texas, is a mid-season bloomer. In spring, and early summer, this well-behaved plant, in low-growing, compact clumps with pale-green foliage, is nice, if unobtrusive, at the front of a lightly shaded border. It becomes far more noteworthy during its bloom period in July, when few other plants are flowering. The inflorescence has the appearance of a finely textured fringe running down one side of its stem, especially dramatic when backlighting emphasizes the display.

Taking into consideration the specific growth characteristics and natural habitat of these grasses, or any others to be incorporated into a garden setting, will help keep maintenance requirements at a minimum.

MAINTENANCE

In my own garden, once-a-year removal of old growth is a basic chore, of course, and then, mindful of the ongoing, precarious balance between control and chaos that a garden represents, I periodically tidy things up. (With grasses, it seems particularly important to keep the design coherent, lest “casual” degenerate to “negligent!”)

After a soaking rain, I will check to be sure the edges are still clearly defined, and whack back unruly stragglers. I pull up errant seedlings while they are still small, and divide any clumps that are starting to look unruly, for even a well-behaved clump grass will eventually outgrow its allotted space. Then, with a little time and energy to spare, I will pot up the divisions or sprouts and replant them elsewhere on my property. It seems only right to return to the wild what we have taken from it, restoring to the prairie landscape those grasses that once dominated it.