The autumn garden is full of late-season color: bold dahlias and asters, pastel Japanese anemones, dusky chrysanthemums, and sunny goldenrods. But there is another group of plants flowering at this time, although the "blossoms" are not quite what you might expect. Ornamental grasses are in their full glory during the golden days of fall.
All summer, these warm-season grasses have produced foliage...and more foliage. Some feature delicate arching sprays; others form clumps, filling in the holes where spring bulbs or early perennials once bloomed. The tall, more upright forms take on the silhouettes of specimen plants and occupy spaces where small shrubs or trees might be at home. And the low-growing, mounding varieties manage to play off their neighboring annuals, perennials, or even dwarf conifers with contrasting texture and color. Ornamental grasses are some of the most versatile plants in the garden, offering fine lines with feathery flowers.
The range of distinctive foliage includes blue, chartreuse, burgundy, gold, green with white stripes, and even black. Ornamental grasses are adaptable enough to thrive in a wide variety of sites. Although most prefer full sun and fertile, well-drained soil, there are grasses for shade, wet soil, pond and stream banks, slopes, or sandy soils. But which ones are the best? Which ones can stand up to cold, snow, wet springs, and clay soils — and still come back strong? Which ones will hold their tawny color and flower plumes throughout winter without breaking form and shattering seedheads? And, most importantly, which ones will prove not to be invasive thugs by setting thousands of seeds and threatening our natural landscapes?
Some of the better grasses that have performed reliably in the Chicago area include the following:
- Annual fountain grass (Pennisetum setaceum) The arching green foliage forms large mounds and sends up pink bottlebrush flower heads. It is not hardy but is a good choice for containers or massed in annual beds. 'Rubrum' is an outstanding 4-foot, burgundy-foliaged cultivar.
- Big bluestem and little bluestem (Andropogon gerardii and Schizachyrium scoparium) The bluestems are true native prairie grasses suitable for naturalistic areas, prairie gardens, or erosion control. Big bluestem, a tallgrass prairie native, grows 4 to 6 feet in a clumping form, producing purple spiked flower heads that give it the common name of "turkey foot." Little bluestem grows 2 to 3 feet with a clumping form that becomes more vertical as the grass matures. Its blue base turns red in fall, and the flower heads are silver. 'Blaze' and 'Carousel' are recommended cultivars for fall color and winter interest.
- Blue fescue (Festuca glauca) This fine, quite small grass, under 12 inches, assumes a mounding form but produces silvery blue, needlelike leaves. Flowers often fail to appear. It is a good grass for the front of the border or for a ground-cover effect. 'Elijah Blue' is a preferred cultivar.
- 'Dallas Blues' switch grass (Panicum virgatum 'Dallas Blues') A highly recommended cultivar of the Midwest's native switch grass, 'Dallas Blues' has broad, very blue leaves that form a loose clump at first, but mature into an upward, slightly open habit. Very large, long-lasting plum-colored plumes form in September and make excellent cut flowers. This beautiful grass is planted in great masses at the Chicago Botanic Garden's Evening Island.
- Fountain grass (Pennisetum alopecuroides) Just as its name implies, this grass's spraylike foliage forms dense 3- to 4-foot green mounds. White foxtail flower heads form on long, curving stems in late summer. It is a good grass for massing or in the middle of a border, and 'Hameln' is a recommended 2- to 3-foot dwarf form.
- 'Karl Foerster' feather reed grass (Calamagrostis x acutiflora 'Karl Foerster') 'Karl Foerster' is a trouble-free, 4- to 5-foot upright grass that is stunning when massed or singled out as a vertical statement. The brown flower heads form early and last for months. The plant tolerates heavy clay soil, drought and partial shade, retaining its tan color and seed heads in winter. This is another featured grass at the Garden's Evening Island, where thousands wave in the wind like brown velvet.
- Northern sea oats (Chasmanthium latifolium) This grass is a loose, medium-sized, 3- to 4-foot clump with broad leaves resembling bamboo. It is ideal for shady or damp conditions. Flat, maroon seed heads develop in June but turn bronze in autumn and remain attractive all winter. This grass is a good choice for dried arrangements.
- Scottish hair grass (Deschampsia caespitosa 'Schottland') This is a cool-season, 2- to 3-foot grass that produces its delicate, fuzzy yellow flower heads early in the season. Dark green, very fine foliage turns tawny as the season progresses. 'Schottland' is strongly recommended for massing when a delicate texture is desired.
- Tall moor grass (Molinia caerulea spp. arundinacea 'Skyracer') A tall, 7-foot grass that is quite effective in groups, 'Skyracer' features purple flower panicles held high above the foliage. This grass turns an attractive yellow in autumn.