The ornamental grass pampas grass (Cortaderia selloana) is a popular landscape feature recognized for its dramatic height and feathery plumes. Originating from South America, this perennial plant is prized for its tolerance to poor soil conditions and drought resistance. Pampas grass spreads aggressively under favorable conditions, leading to concerns about its invasive tendencies in many regions. This vigorous growth habit means a plant chosen for its aesthetic appeal can become a considerable maintenance challenge.
How Pampas Grass Propagates
Pampas grass employs two distinct mechanisms for its spread: seed dispersal and physical expansion. The most significant factor in its aggressive colonization is the sheer volume of viable seeds it produces. A single mature female plant can produce up to 100,000 seeds per plume, potentially releasing over a million seeds annually.
These exceptionally light seeds are dispersed widely by wind, allowing them to travel great distances from the parent plant. Pampas grass is a dioecious species, meaning it has separate male and female plants; only female plants produce fertile seeds. Male plants produce pollen but lack the showy, silky plumes that make female plants desirable for planting.
The second method of propagation is the slow, outward expansion of the root structure, known as a clumping growth habit. Established pampas grass maintains its massive size through the division of its crown and rhizomes, which are underground stems. This process results in large, dense clumps that can reach several feet in diameter. Propagating both by scattering seed and expanding its root mass makes it a formidable presence in the landscape.
Controlling Established Clumps
Addressing a mature pampas grass clump requires caution and considerable physical effort due to the plant’s size and structure. The foliage blades of Cortaderia selloana have razor-sharp edges, necessitating heavy protective gear, including gloves and long sleeves. The first step involves cutting the massive clump back to a short stubble, 2 to 4 inches above the ground, which exposes the dense crown and root system.
Physical removal is demanding because the root system can extend down 2 to 4 feet, creating a dense, heavy mass. For established plants, use an axe or sharp shovel to chop the crown into smaller, manageable pieces before digging them out. The goal is to remove the entire living crown, as the plant readily regrows from any remaining pieces of this central base.
For severe infestations or large clumps, a targeted chemical approach is often the most effective solution. Herbicides containing active ingredients like glyphosate are recommended for permanent eradication. The “cut-and-paint” method is highly effective, applying a concentrated solution immediately to the freshly cut crown surface. This targeted application minimizes chemical exposure to the surrounding soil, though multiple applications may be necessary to completely kill the robust root crown.
Choosing and Planting Varieties
When selecting pampas grass, proactive choices can significantly reduce the risk of aggressive spreading. The primary preventative measure is selecting specific cultivars known for reduced or non-existent seed production, often called sterile varieties. While some are marketed as sterile, investigate local invasive species regulations, as even these can occasionally spread.
A popular and less aggressive choice is the dwarf variety ‘Pumila’ (Cortaderia selloana ‘Pumila’), which typically matures at five to seven feet, making it more manageable than the standard ten-foot species. Purchasing plants propagated by division, rather than grown from seed, guarantees receiving the desired cultivar traits, including reduced fertility. Female plants are usually chosen for division because they have the most attractive plumes.
Proper placement is also a crucial strategy for containing the plant’s growth. Given the large size and sharp foliage, pampas grass should be positioned away from walkways, play areas, and property lines to allow for its eventual spread. Standard varieties require spacing of at least six to eight feet apart. Dwarf varieties can also be grown successfully in large containers, which prevents the spread of both seeds and rhizomes into the landscape.