The ornamental grass known as Pampas Grass (Cortaderia selloana) is a large perennial native to South America. It has gained popularity worldwide due to its vigorous growth rate, allowing it to quickly establish a dominant presence in a garden setting. Understanding this rapid development is important for anyone considering it for their landscape.
Quantitative Growth Rate of Established Plants
Once established, Cortaderia selloana exhibits notably rapid annual growth. Under ideal conditions, a plant can add several feet to its height in a single growing season. Mature foliage typically reaches 6 to 10 feet tall, with the silvery-white or pink plumes adding 2 to 3 feet, sometimes reaching 12 feet overall. In warm climates, growth can be quick, sometimes increasing up to an inch per day during peak summer months.
The plant’s horizontal spread is equally impressive, forming a dense, clump-forming tussock that can stretch up to 8 feet wide. This rapid expansion is driven by the dense, fibrous root system spreading laterally. This substantial expansion requires established plants to have significant space and annual management to keep their size in check.
Time Required for Initial Establishment
Although the mature growth rate is fast, the plant requires a foundational period for its root system to fully develop. When planted as a seedling or small transplant, the first year is primarily dedicated to root establishment beneath the soil. Visible growth above ground is slower during this phase compared to subsequent years. New plants require consistent watering during this initial period to help the roots take hold.
If grown from seed, the timeline is extended, and the plant will not typically produce its recognizable plumes for the first two years. The plant is considered fully established and capable of exhibiting its full growth rate after approximately two to four years. At this point, the plant begins to reach its mature size and demands the most attention in terms of space and maintenance.
Environmental Factors That Accelerate or Slow Growth
The speed at which Pampas Grass grows depends highly on specific environmental conditions. Maximum growth occurs when the plant is situated in a location receiving full sun, defined as a minimum of six hours of direct sunlight per day. Planting in partial shade will slow the growth rate, resulting in shorter foliage and fewer plumes. The availability of soil nutrients also modulates the speed of development.
While Cortaderia selloana tolerates poor soils, its fastest growth is observed in rich, loamy, and well-draining soil. Adding organic matter and nutrients can significantly accelerate vegetative growth. Consistent moisture, particularly during dry spells, supports a faster growth rate, though the plant becomes highly drought-tolerant once its extensive root system is established.
Climatic conditions dictate the length of the growing season and overall size. Pampas Grass thrives in warm climates (USDA zones 7 through 11). In cooler parts of its range, the plant goes dormant in winter, halting growth for several months. This dormancy shortens the annual growing period, resulting in a slower overall expansion rate compared to regions with extended growing seasons.
Managing Rapid Growth Through Maintenance
The plant’s rapid growth necessitates specific annual maintenance to control its size and maintain vigor. The most important task is annual pruning, which should occur in late winter or early spring before the new growth cycle begins. The foliage mass should be cut back hard, typically to about 12 inches above the ground. This severe cut clears out the old, dead material and stimulates a fresh flush of growth.
Due to the sharpness of the leaf margins, often described as razor-edged, it is necessary to wear heavy gloves, long sleeves, and eye protection during this annual task. Beyond yearly cutting, managing the horizontal spread requires periodic division. To maintain the plant’s health and prevent the center from dying out, large, established clumps should be divided every few years. This process involves physically separating sections of the root mass and replanting them or removing them entirely.