Pink Muhly Grass, or Muhlenbergia capillaris, has become a favored choice for late-season garden color. Gardeners are often drawn to its fine texture and dramatic fall display, but questions about its spread frequently arise. This article clarifies the botanical and ecological status of this plant, explaining why it is classified as merely aggressive rather than ecologically invasive.
Understanding the Definition of Invasive
The term “invasive species” carries a specific ecological and regulatory meaning. An invasive species must satisfy two strict criteria: it must be non-native to the ecosystem under consideration, and its introduction must cause, or be likely to cause, environmental or economic harm, or harm to human health. This definition is codified in the United States by Executive Order 13112.
A plant labeled “aggressive,” in contrast, is one that spreads rapidly and readily within a localized area, such as a garden bed. An aggressive plant may be challenging for a gardener to manage, but it does not displace beneficial native species in wild landscapes to the point of causing ecological harm.
Pink Muhly Grass: Native Status and Spread Characteristics
Pink Muhly Grass, Muhlenbergia capillaris, is a warm-season, perennial grass native to large sections of the United States. Its natural range extends from Massachusetts south to Florida and west to Kansas and Texas, where it thrives in prairies, pine barrens, and open woodlands. Because it naturally occurs across a significant portion of the country, it is generally not classified as an invasive species by state or federal regulatory bodies.
The grass exhibits a clump-forming growth habit. It does not spread via aggressive underground stems, known as rhizomes. Its primary method of spread is through self-seeding, where the lightweight seeds from the spectacular fall plumes are dispersed by wind and germinate in nearby disturbed soil. This localized spread can make it seem aggressive in a garden setting, but it is not a true ecological threat.
Managing Aggressive Self-Seeding in the Landscape
Since Muhlenbergia capillaris is a clumping grass that primarily spreads by seed, controlling its population focuses on reducing seed dispersal. The key to mitigating aggressive self-seeding is to remove the feathery plumes before the seeds fully mature. This can be done by cutting back the dried foliage and seed heads in late winter or early spring, just before the new growth begins.
Gardeners should cut the grass back to a height of approximately six inches above the ground. Beyond managing its seeds, the plant’s dense, fibrous root system occasionally needs attention, as the central crown can die out over time. To rejuvenate the plant and maintain spacing, the clumps can be propagated by division every few years, using a sharp tool to split the root ball and replant fresh sections.