Panicum virgatum ‘Shenandoah’ is a widely planted ornamental grass, valued for its striking seasonal color and sturdy structure. As a cultivar of native North American switchgrass, it is popular in gardens but often raises questions due to its vigorous growth habit. Gardeners frequently confuse its ability to rapidly expand within a cultivated area with being an invasive species.
Identifying Shenandoah Switchgrass
The ‘Shenandoah’ cultivar is a clumping, warm-season perennial grass that develops an upright, vase-shaped structure. It typically reaches a mature height of 3 to 5 feet, with an almost equal spread. Its dramatic foliage coloration emerges blue-green in spring before the leaf tips develop a reddish tint by mid-summer. This color intensifies to a deep, wine-burgundy hue by autumn. In late summer, airy, reddish-pink panicles emerge above the foliage, adding fine texture that persists into the winter.
Aggressive Spreader vs. True Invasive
The distinction between an aggressive garden plant and an invasive species is defined by ecological impact and origin. An aggressive plant, such as ‘Shenandoah’, is typically a native species or cultivar that spreads quickly and can outcompete other plants within a managed landscape. This tendency is primarily a nuisance to the gardener who must maintain boundaries, but it does not cause widespread ecological harm. The parent species, Panicum virgatum, is native to the United States.
Conversely, a true invasive species is defined by law as non-native to the ecosystem and one whose introduction causes or is likely to cause environmental or economic harm. Invasive plants escape cultivation, disrupt local biodiversity, and displace native flora because they lack natural predators or diseases to keep their populations in check. While ‘Shenandoah’ is a vigorous self-seeder and can slowly spread via its rhizomatous root system, it is generally not classified as an ecological invasive species across most of the U.S. Instead, it is best described as an aggressive spreader that requires management within the confines of a garden bed.
Controlling Its Spread in the Landscape
Managing the spread of ‘Shenandoah’ switchgrass involves two main strategies: controlling self-seeding and limiting clump expansion. To prevent the grass from producing unwanted volunteer seedlings, the airy flower panicles should be removed through deadheading. This action is most effective in late summer or early fall, before the small seeds fully mature and are dispersed. Preventing self-seeding is the most direct way to keep the grass contained to its original planting area.
Since ‘Shenandoah’ is a clumping grass that expands outward over time, periodic division is necessary to manage its size. The extensive, fibrous root system will eventually cause the center of the clump to die out, signaling the need for division. Using a sharp spade, the clump should be divided every three to five years in the early spring, just as new growth begins. This practice maintains the plant’s vigor and keeps its footprint manageable within the landscape design.