Two North American Alternatives to Invasive Ornamental Grasses
Try switchgrass or prairie dropseed.
Ornamental grasses have become increasingly popular as modern tastes have shifted to more naturalistic garden designs. Grasses bring year-round interest, movement, structure and seasonal changes of palette that enhance every garden.
Unfortunately, several popular non-native grasses have escaped gardens to invade natural areas, where they can displace native species. Exotic grasses do not support wildlife in the same way native plants do, and recent studies point to invasive grasses’ potential to worsen wildfires and their effects. (Read one paper on the subject here.) Two common ornamental grasses to omit from the garden are Chinese silver grass (Miscanthus sinensis) and fountaingrasses (Pennisetum).
Miscanthus sinensis, also known as zebra grass, porcupine grass or maiden grass, has many cultivars, including ‘Morning Light’, ‘Flamingo’, ‘Ghana’ and ‘Adagio’ among many others. Though some of these are advertised to be sterile, cross-pollination with other cultivars has been shown to result in fertile, windborne seeds. Despite being listed as an invasive species in more than a dozen states, and regulated or even banned in several, M. sinensis is still being sold and planted widely.
Two other popular ornamental grasses, Chinese fountaingrass (Pennisetum alopecuroides), and African fountaingrass (P. setaceum), are also now recognized as invasive. As early as 2012, the Exotic Plant Management Team of the National Park Service and the US Department of Interior made Chinese fountaingrass the subject of an Invasive Plant Alert. The alert included a warning that its cultivars, including ‘Hameln’, ‘Cassian’, ‘Red Head’, ‘Mondry’, ‘Little Honey’, ‘Little Bunny’ and others, “do not come true from seed” and have high invasive potential. These plants already have naturalized throughout much of the Northeast, Mid-Atlantic and Midwest regions.
Meanwhile, African fountaingrass is considered invasive anywhere outside its native range in Northern Africa. It is already naturalized in the Southwest and the Southeast. It has been shown to increase fire intensity where it has naturalized in Hawaii and California.
We do have excellent, garden-worthy, native alternatives to these exotic grasses. Switch grass (Panicum virgatum) and prairie dropseed (Sporobolus heterolepsis) are two beautiful North American grasses that can fill the same garden roles without risk of ecological harm.
Plant Switchgrass Instead of Silver Grass
Switchgrass is just as attractive as Chinese silver grass, just as easy to grow and just as versatile. A denizen of America’s tall-grass prairies and meadows from the East Coast through the Central Plains and into the Interior West, it has deep roots that make it drought tolerant. It’s also deer resistant. It prefers full sun and actually does best in poor soil. It needs no fertilizer and rarely requires supplemental water. These virtues have prompted recent development of numerous cultivars in varied sizes, shapes and colors.
The cultivar ‘Heavy Metal’ provides a big impression. It grows up to five feet tall, with strappy leaves to almost a half-inch wide. These are steel blue in summer, turning bronze for fall and winter, when the grass provides texture, movement and contrast to evergreen shrubs and seeds and cover for songbirds.
‘Cloud Nine’ stands even taller, reaching seven to eight feet, making it a great substitute for the largest Miscanthus cultivars.
‘Northwind,’ a selection discovered by Roy Diblik of Northwind Perennial Farm and named the Perennial Plant of the Year in 2014, is the most upright of the tall switchgrasses. At five to six feet tall and narrow in habit, it provides a great vertical element in the garden.
For a smaller plant, there’s ‘Shenandoah’, at three to four feet tall with a graceful vase shape that complements both shrubs and perennials. The tips of its narrow leaves turn red and burgundy during the summer, and when it blooms, its tiny flowers form an ethereal cloud above the leaves.
The similarly sized ‘Ruby Ribbons’ boasts multicolored leaves that show shades of red, purple and green all summer long. It is dazzling in the fall, especially paired with purple asters.
The smallest of the switchgrass cultivars is ‘Cape Breeze’. At about two feet tall and wide, with leaves in a soft blue-green, it looks lovely at the front of the border—or along a sunny curb, since switchgrass can tolerate road salt.
All of the switchgrasses do best in full sun and well-drained soil. Too much shade or soil that is too rich can cause the taller varieties to flop later in the season. They can handle occasional inundation, but most of the cultivars do not perform well in persistently soggy soil. Cold-hardy to USDA Zone 4, these are warm-season, clump-forming grasses. Cut them back in late winter or early spring just before the new shoots emerge.
Plant Prairie Dropseed Instead of Fountaingrass
Prairie dropseed (Sporobolus heterolepsis) is the ideal native alternative to exotic fountaingrasses (Pennisetum). It has the same charming shape, with very fine-textured leaves that reach out from its center in graceful arches. It grows only two to three feet in height before blooming in midsummer. The tiny flowers are held on delicate stems that stretch another 18 to 24 inches above the leaves and then branch into dancing clusters. They develop golden seeds.
Most surprising for a grass, the blooming stalks are fragrant! Hard to define, the scent has been described as similar to popcorn, green coffee beans, cilantro or anise. The scent fades as the seeds ripen in fall.
Prairie dropseed may be used effectively in a sunny garden as a unifying matrix, tying a flowerbed together visually and covering the soil to eliminate the need for mulch. (Read more about matrix gardening.) It looks great in front of shrubs in foundation plantings, and it is small and elegant enough to form a well-behaved edge along a sidewalk or path. It is spectacular massed as a lawn substitute or as part of a prairie planting.
Prairie dropseed turns gold in October and continues to add structure to perennial beds even in winter. It is deciduous, but holds its shape pretty well even after being buried in snow. By late winter, the plants look rather quirky – somewhat like Cousin Itt of the Addams family. In spring, when green shoots are starting to show, a quick haircut will tidy things up.
Prairie dropseed is native to American prairies and dry meadows and is found in at least 26 states from the Canadian border to Georgia and west as far as New Mexico, but it is most common in the Central Plains states. Like switchgrass, it is a warm-season bunch grass. It does not spread itself by runners and, despite its name, does not easily spread by seed. The “dropseed” in the common name apparently refers to the fact that ripe seeds do fall to the ground, where they may be eaten by birds and small mammals. They do not seem to germinate easily. You are not likely to see it popping up around the garden.
Prairie dropseed is happy in Zones 3 to 9. A true prairie plant, it prefers dry and even rocky soil in full sun. It never needs fertilizer and remains unbothered by deer or rabbits. Its roots form a deep network ideal for stabilizing slopes and withstanding drought. As elegant as it may be for flower beds, it also proves ideal for roadsides or traffic islands, since it is undeniably tough as well as salt tolerant.
There are two prairie dropseed cultivars now on the market. ‘Tara’ and ‘Morning Mist’ both stay smaller than the species, at only 18 to 24 inches tall, and they grow more upright than fountain shaped. ‘Tara’ produces abundant flowers in late summer that stand almost straight up above its short foliage, rather than arching from the center. The reddish flowering stems of ‘Morning Mist’ are upright as well.
Prairie dropseed grows slowly compared to many grasses. Plugs can take up to four years to establish, and even nursery-grown container plants may need a couple of seasons before their roots form a dense, drought-resistant clump. Once established, though, prairie dropseed is long-lived and very low maintenance.
