Fountain grass, a perennial plant in the Pennisetum genus, is a widely planted ornamental grass celebrated for its graceful, bottle-brush plumes and mounding growth habit. However, specific species have become highly aggressive invaders in many regions worldwide. Its rapid spread and ability to thrive in harsh environments present a significant ecological challenge, especially in arid and semi-arid regions. The question is which varieties pose a serious threat to native ecosystems.
Distinguishing Invasive Fountain Grass Species
The primary invasive culprit is Pennisetum setaceum, often known as crimson fountain grass, which is native to North Africa, the Middle East, and Southwest Asia. This species forms dense, perennial bunches up to three feet tall, characterized by feathery, pink-to-purplish inflorescences. Its invasive potential lies in its ability to produce copious, wind-dispersed seeds that remain viable in the soil for at least six to seven years.
Many commercial cultivars, such as ‘Hameln’ or ‘Purple Fountain Grass’ (‘Rubrum’), are sold as non-invasive alternatives, but this distinction is not always reliable. The green-leaved, wild-type P. setaceum is the highly problematic, seed-producing species that escapes cultivation. When identifying the invasive type, look for the tall, green-leaved bunch grass with pale pink or purple spikes that readily shatter their seeds, a characteristic often absent in the darker-foliaged ornamental varieties.
Geographic Distribution and Official Invasive Status
The aggressive spread of P. setaceum is severe in warmer climates across the globe, including Australia, South Africa, and the Mediterranean. In the United States, it is widely established in the Southwestern US, including Arizona, Southern California, and Hawaii, where it poses a significant threat to delicate desert and dry forest ecosystems. It is also found in states like Colorado, Florida, Louisiana, and Tennessee, highlighting its adaptability.
Because the grass is detrimental, it has been given official legal designations to restrict its sale and movement. It is listed as a noxious weed in states like Hawaii and Nevada, formally recognizing its ecological damage. In California, the species is given a Cal-IPC rank of “Moderate,” indicating substantial ecological impacts on plant communities. These official designations prohibit or strongly discourage the propagation and planting of the fertile species within those jurisdictions.
Ecological Impact: Altering Fire Cycles and Native Habitats
The most concerning ecological impact of invasive fountain grass is its role in altering the natural fire cycle of non-fire-adapted ecosystems. Fountain grass is highly fire-adapted, and its dense, dry material acts as an easily ignitable “fine fuel” that significantly increases the overall fuel load. This increased fuel load leads to fires that are hotter, spread more quickly, and occur much more frequently than they would naturally.
Native desert shrublands and Hawaiian dry forests are not adapted to this new fire regime; the intense heat easily kills native plants, which often lack the ability to resprout quickly. The invasive grass, however, rapidly re-establishes itself following a burn, resprouting from its base and quickly setting seed, often increasing its density. This positive feedback loop is known as the grass-fire cycle, which systematically eliminates native flora and transforms diverse habitats into low-diversity, grass-dominated monocultures.
Beyond fire, fountain grass outcompetes native species through its efficient use of resources. The plant forms dense stands with extensive root systems, allowing it to monopolize available water and nutrients. This aggressive competition reduces moisture available to surrounding flora, displacing native and endangered species and accelerating the loss of local biodiversity. The sheer density of the grass also prevents native seedlings from establishing, cementing the shift toward an invasive-dominated landscape.
Management Strategies and Non-Invasive Alternatives
Managing established infestations requires persistent effort due to the plant’s deep root system and long-lived seed bank. For small infestations, manual removal is effective, but it is necessary to dig out the entire clump, including the base and roots. Any flower heads must be bagged and destroyed to prevent seed dispersal. This process may need to be repeated annually, as seeds can continue to germinate for many years.
Larger populations often necessitate chemical control, typically using systemic herbicides like glyphosate, which translocate to the roots to kill the entire plant. A common technique involves applying the herbicide to actively growing plants and allowing several weeks for it to take effect before cutting the dead material. Prevention remains the simplest strategy, including cleaning machinery and vehicles that may carry seeds and avoiding planting the fertile species near natural areas.
Non-Invasive Alternatives
Homeowners can choose non-invasive ornamental grasses that provide a similar aesthetic without the ecological risk. Alternatives include native species like Muhly Grass (Muhlenbergia capillaris), which offers delicate pink plumes and is well-behaved in the landscape. Other excellent, regionally appropriate choices are Blue Grama (Bouteloua gracilis) or Prairie Dropseed (Sporobolus heterolepis), which provide beautiful texture and form while supporting local ecosystems.