Pampas grass (Cortaderia selloana) is a large perennial ornamental grass native to the Pampas region of South America. Introduced worldwide for its imposing size and distinctive, feathery plumes, the plant is now recognized as problematic in many regions outside its native range. Its aggressive growth, physical dangers, and environmental impact have given this decorative species a negative reputation.
Aggressive Invasive Growth
The primary concern regarding Pampas grass is its capacity for aggressive, unchecked growth, leading to significant ecological disruption. Female plants produce a prodigious quantity of seeds; a single plume can yield up to 100,000 seeds that are easily dispersed by wind over long distances. This reproductive success allows the plant to quickly colonize disturbed areas and coastal habitats, where it outcompetes native flora.
Once established, Pampas grass forms dense clumps, known as tussocks, that shade out smaller, indigenous plants. This leads to monocultures, drastically reducing local biodiversity. Since it tolerates a wide range of soil conditions and is drought-tolerant, it efficiently takes over various habitat types. It is classified as a noxious weed in many areas, including parts of the western United States.
Significant Physical and Fire Hazards
Pampas grass presents immediate safety risks to people and property. The long, slender leaves have razor-sharp, finely serrated edges that can inflict deep cuts on human skin, earning the plant the nickname “cortadera” (cutter). This characteristic makes routine maintenance, such as pruning, hazardous and difficult without heavy protective gear.
The plant poses a serious fire hazard, especially in dry climates prone to wildfires. Its dense, clumping habit causes it to accumulate a large amount of dry, dead material, or thatch, in its interior. This material makes the plant highly flammable and capable of burning intensely. When ignited, these clumps act as a fuel source and “ladder fuel,” allowing fire to spread rapidly and increase the intensity of wildfires.
Challenges in Removal and Management
Eliminating established Pampas grass is difficult due to the plant’s robust biological structure. The species develops an extensive and tough root system, with roots potentially occupying over 1,000 square feet and reaching depths of up to 11 feet. Mechanical removal of a mature clump often requires heavy equipment, such as an excavator, making the process labor-intensive and costly.
Manual removal is not feasible for large specimens, and remaining root fragments can easily resprout. Effective management often requires chemical control, where systemic herbicides are applied after the leaves have been cut back. However, the size and density of the tussocks limit the effectiveness of the application, often necessitating multiple treatments and ongoing vigilance.
Allergic and Respiratory Irritants
Health concerns relate primarily to airborne irritants. Pampas grass is wind-pollinated, and its plumes release a large volume of pollen, making it a significant allergen for sensitive individuals. Exposure can trigger typical hay fever symptoms, including sneezing, runny nose, and itchy eyes, and can aggravate conditions like asthma.
For those with grass pollen allergies, Pampas grass can extend the allergy season since it often pollinates later than local grasses. The dense tussocks also create a moist environment conducive to harboring mold and mildew. These can become respiratory irritants if the plant is disturbed or located near ventilation intakes.