Switchgrass (Panicum virgatum) is a hardy perennial grass native to North America, spanning a range from Canada to Mexico. The concern about its spread is understandable, given its vigorous nature and tendency to spread in garden settings. However, switchgrass is not classified as an invasive species because it naturally belongs to the North American ecosystem. The debate over its behavior centers on its aggressive growth habit, which allows it to thrive, especially in disturbed or cultivated areas. Understanding its natural mechanisms for expansion is the first step toward effective management.
Defining Aggressive Growth vs. True Invasiveness
The distinction between an aggressive native plant and a truly invasive species is based on scientific criteria. A species is only deemed invasive when it is non-native to the ecosystem under consideration, and its introduction causes economic or environmental harm. This harm typically involves outcompeting native flora, disrupting the food web, or altering ecosystem processes. Switchgrass is a dominant species of the historic tallgrass prairie and is native to the United States and Canada. Its vigor is a characteristic of its success as a native prairie grass, not a threat to the overall ecosystem.
Natural Growth Habits and Propagation
The ability of switchgrass to spread comes from two primary biological mechanisms: rhizomes and seed production. Rhizomes are horizontal underground stems that allow the plant to grow new shoots and roots outward from the main clump. This slow but steady expansion leads to the perception of “running” or “sod-forming” behavior, particularly in certain cultivars. Switchgrass cultivars are generally categorized as either “upland” or “lowland” types, which affects their spread.
Upland types, which are often shorter and more cold-tolerant, tend to have more vigorous, sod-forming rhizomes. Conversely, lowland types may appear to have a more distinct bunchgrass habit, though they still use short rhizomes to expand the clump. Beyond rhizomes, the plant produces tiny seeds in delicate, airy panicles that can be carried to new locations by wind or wildlife. Self-sowing is typically minimal in well-maintained settings, but new plants can establish from seed under ideal, often disturbed, conditions.
Native Status and Ecological Significance
Switchgrass is a long-lived perennial and one of the signature species of the North American tallgrass prairie. Its deep-rooted structure, which can extend ten feet or more into the soil, provides exceptional soil conservation benefits. The extensive root mass helps to hold soil in place, making it highly effective for erosion control and managing runoff. The grass plays a significant role in supporting wildlife within its native habitat. Its dense, upright growth provides excellent cover for nesting birds, and seeds persisting through the winter are an important food source for songbirds.
Practical Management of Switchgrass Spread
Managing switchgrass spread requires a two-pronged approach targeting both rhizomes and seeds. To manage expansion from underground stems, install physical root barriers around the planting area. These barriers, typically plastic or metal sheeting, must be set vertically into the ground to contain the rhizomes. For established clumps, dividing the grass every few years maintains vigor and controls size; this is best performed in early spring by removing sections. To prevent unwanted seedlings, cut back the feathery flower heads in late summer or early fall before the seeds mature and drop to the soil.