Shenandoah switchgrass (Panicum virgatum ‘Shenandoah’) is a widely favored ornamental grass, appreciated for its upright form and vibrant fall color. Gardeners often question if this popular grass is truly invasive or simply exhibits vigorous growth habits.
Defining Invasive Versus Aggressive Growth
Understanding the distinction between invasive and aggressive plants is fundamental for responsible gardening.
An invasive species is a non-native organism whose introduction to an ecosystem causes environmental or economic harm, or harm to human health. These plants typically outcompete native flora, disrupt natural ecosystems, and can lead to a reduction in biodiversity by forming monocultures. They spread rapidly and are difficult to control, often lacking natural predators or diseases in their new environment.
In contrast, an aggressive plant describes a species that spreads readily and rapidly within its native range. Such plants are well-adapted to their environment and can colonize new areas efficiently through various reproductive strategies, such as rhizomes or prolific seeding. While their spreading nature might be challenging for gardeners seeking a tidy landscape, a native plant exhibiting aggressive growth does not typically cause ecological harm. It remains a part of the natural ecosystem, contributing to its balance and supporting native wildlife.
Shenandoah Switchgrass Native Status and Behavior
Switchgrass (Panicum virgatum) is a true native of North American prairies, ranging across much of the central and eastern United States and parts of Canada. As a cultivated variety of this native species, ‘Shenandoah’ shares the inherent characteristics of its wild counterpart.
Its deep root system and rhizomatous growth habit allow it to form dense clumps and spread horizontally underground.
The natural behavior of switchgrass includes prolific self-seeding, especially in disturbed soils or open areas. Mature seed heads disperse numerous seeds, which readily germinate when conditions are favorable. While beneficial in a prairie ecosystem, these spreading mechanisms can lead gardeners to perceive ‘Shenandoah’ as “invasive.” However, its native status means it interacts positively with local ecosystems, unlike non-native invasive species.
Managing Its Spreading Tendencies
Gardeners can effectively manage the vigorous spreading tendencies of Shenandoah switchgrass to keep it within desired bounds.
One approach involves planting it in areas where its spread can be contained, such as within a perennial border where surrounding plants can compete with its rhizomes. Installing a physical root barrier, made of plastic or metal, around the planting area can also effectively restrict its underground expansion. These barriers, typically buried 10 to 18 inches deep, prevent rhizomes from venturing into unwanted spaces.
Regular division of established clumps is another method to control spread and rejuvenate the plant. Every three to five years, digging up the plant in early spring and dividing the root ball allows gardeners to remove excess growth and replant smaller sections.
To minimize self-seeding, deadheading the mature seed heads in late fall or early winter before they fully ripen can significantly reduce the number of viable seeds dispersed. This proactive step helps prevent unwanted seedlings from emerging in subsequent growing seasons.
Ecological Benefits of Native Switchgrass
Beyond its ornamental appeal, native switchgrass, including the ‘Shenandoah’ cultivar, offers significant ecological benefits to the landscape.
Its dense growth provides valuable cover and nesting sites for various bird species, particularly ground-nesting birds, throughout the year. The sturdy stems and seed heads serve as a food source for birds during winter months, contributing to biodiversity in the garden.
The extensive root system of switchgrass plays a crucial role in soil health and erosion control. These deep roots stabilize soil, prevent runoff, and contribute organic matter, improving soil structure over time.
As a drought-tolerant native, it requires minimal supplemental irrigation once established, making it a sustainable choice for water-wise landscaping. Its resilience and contribution to local ecosystems highlight its value as a beneficial plant in many garden settings.