Prairie dropseed, Sporobolus heterolepis

Prairie dropseed, Sporobolus heterolepis, in mid-summer.

Prairie dropseed, Sporobolus heterolepis, is a warm season grass native to the tallgrass and mixed grass prairies of central North America that is also a popular low-maintenance ornamental landscape plant in zones 3 to 9. Found mainly on the Great Plains from Texas north to southern Saskatchewan, this long-lived perennial clump-forming grass also occurs less commonly in certain habitats in scattered pockets in the eastern Midwest and Northeast to Quebec. It is native to about the southern half of Wisconsin. It was was named a Plant of Merit by the Missouri Botanical Garden in 2005 and was selected as the Wisconsin Nursery and Landscape Association’s herbaceous perennial of the year 2018.

Prairie dropseed in late May at Olbrich Botanical Gardens, Madison, WI.

Plants grow 2-3 feet tall and wide from a fibrous root mass, forming an arching, fountain-like mound of foliage with a fine texture. The smooth, medium green linear leaves are very narrow and either flat or rolled. In fall, the dense tufts of foliage turn an attractive golden bronze, often with orange or copper highlights, and resists flattening by snow so this plant can provide winter interest if not cut back until spring.

Prairie dropseed flowering (L) and in seed (R).

In mid- to late summer, small pink and brown-tinted flowers are produced in airy, 3-8 inch long flower heads with a narrowly pyramidal silhouette. One or more stout but slender culms develop from the center of each leafy clump. The wiry, open branching panicles terminating in individual spikelets are held well above the foliage and add movement in the garden. Each spikelet has two glumes of different lengths, a lemma, a membranous palea and a floret. The wind-pollinated florets are highly unusual for a grass, having a fragrance variously described as vaguely reminiscent of coriander, licorice, popcorn or sunflower seeds. The florets are followed by small, smooth, hardened rounded seeds (technically an achene, a type of fruit, rather than the more normal caryopsis or grain that most grasses produce) within tan hulls, which drop to the ground when mature – hence the common name of dropseed. Birds such as sparrows and juncos, and other animals, feed on the seeds; Native Americans ground the seed to make flour. Although it does produce seed it generally does not self-sow freely in gardens.

New growth of prairie dropseed in spring.

Grow prairie dropseed in full sun in most types of well-drained soil. Although it prefers dry, rocky soils it does fine in heavy clay, too. It tolerates drought but also periodic inundation so can be used on the upper edges of rain gardens where it doesn’t remain too wet. It has no serious pest problems, is not favored by deer (although it may be grazed), and is tolerant of juglone so it can thrive around black walnuts. Once established it needs little care other than pulling, cutting, or burning the old foliage off in late winter or early spring before new growth begins.

Prairie dropseed combined with fall-blooming sedums and alliums.

Use prairie dropseed in perennial or mixed borders, naturalistic plantings, meadows, and restored prairies and roadside revegetation. It is a good addition to rain gardens and aids in erosion control. Its fine, flowing appearance is a good contrast to plants with bold foliage or upright form. It makes a great filler between many types of herbaceous perennials but especially those native to prairies, too, such as purple coneflower (Echinacea purpurea), small goldenrods, liatris, blackeyed Susan (Rudbeckia fulgida var. fulgida), and butterfly weed (Asclepias tuberosa). Planted in large masses it can be used as a tall ground cover or can be used to create a distinctive border. It can also be used as an accent specimen plant. It is particularly nice when positioned so the flower and seed heads are backlit.

Prairie dropseed with purple Verbena bonariensis and other ornamental plants.

It can be the dominant plant in a “matrix planting” where a single species, or handful of species form a matrix into which other plants are blended. In its native habitats it is commonly associated with little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardii var. gerardii), grama grasses (Bouteloua spp.), panic grass (Panicum spp.), Indiangrass (Sorghastrum nutans), leadplant (Amorpha canescens), green milkweed (Asclepias viridiflora), coreopsis (Coreopsis spp.), purple sorrel (Oxalis violacea), phlox (Phlox spp.), and yellow cone flower (Ratibida pinnata) among other plants.

Sporobolis heterolepis ‘Tara’ at Olbrich Botanical Gardens, Madison, WI.

Although prairie dropseed can be grown from seed, it is slow growing, taking about four years to reach blooming size and so it is often started from plugs (in prairie restoration) or divisions (in gardens). If growing from seed, sow outdoors in fall or stratify in dry soil for 10 weeks if planting indoors in spring. Divisions, taken in spring once growth resumes, can take a long time to establish but clumps rarely require dividing and are very dense and difficult to divide.

Generally only the species is available, however, plantsman Roy Diblik of Northwind Perennial Farms in Burlington, WI discovered a dwarf selection in 1994 in the Kettle Moraine area and introduced it as the cultivar ‘Tara’.

– Susan Mahr, University of Wisconsin – Madison