A fast-growing and large-clumping ornamental grass, pampas grass gets its name from the lowland plain of South America, the Pampas, where it is native. With graceful, arching leaves and amazingly ornamental flower and seed plumes, a clump of pampas grass is showiest in late summer through late autumn. It grows best where winters are not severely cold.
Although any species of grass that belongs to the botanical genus Cortaderia is generally called "pampas grass," it is most often a name assigned to one species, Cortaderia selloana. This species is native to the temperate regions of central Chile, central and northern Argentina and extreme southern Brazil.
Pampas grass is an evergreen perennial grass that forms a dense clump, called a tussock. Its long leaves arch gracefully, creating a mature plant with a height of 8 to 10 feet and diameter of 5 to 7 feet.
Blades of this grass are stiff, flat and narrowly linear in shape. Usually the leaves are medium green and have matte finish, slightly blue-green at times. The margins or edges of the grass blades are thin and sharp, mainly discovered after a paper-cut occurs if a bare hand strokes the blade. In regions with mild winters the foliage is evergreen, but many blades dry in the autumn, turning tan, and then replaced and masked by new emerging leaves the next growing season.
In late summer, erect stems rise above the arching mass of foliage and bear plume-like flowers that are beautiful. The individual flowers, called spikelets, are tiny and pink or purple tinted silver on the plume, called a panicle. The panicle is pyramid-shaped or oblong. After the flowers are pollinated in the wind, they ripen into persistent, soft, silvery beige seeds. The dried seed heads further bleach to nearly white over the winter months.
Grow pampas grass in full sun exposures, receiving at least 6 to 8 hours of direct sunlight daily. The soil must be fertile and moist, but well-draining to prevent any rotting of roots or lower stems. Previous year's foliage and seed heads should be removed each late winter before new grass blades emerge. Pruning the stems or taking a chainsaw blade into the clump of stems to reduce the plant to a height of 2 to 3 feet is common practice.
Grow pampas grass as a healthy, returning perennial plant in USDA Hardiness zones 7 through 11. Western North American gardeners may be more familiar with the Sunset Climate Zone rating for this grass, being best grown in zones H1, and 3 through 24. Selected varieties of pampas grass may be better suited for slightly colder or more tropical climates than the general hardiness ratings listed. Consult the plant label or literature to learn specific hardiness ratings of a specific variety, such as sun stripe, pumila or silver comet.
In warm-winter regions, pampas grass quickly spreads in the landscape thanks to the wind dispersal of its tiny seeds. Across the southern United States, for example, pampas grass is often regarded as invasive and may not be recommended for garden use. In some regions, such as Southern California or Hawaii, this grass species may be prohibited from sale or culture.