Purple Fountain Grass (Pennisetum setaceum ‘Rubrum’) is highly valued in landscaping for its dramatic, arching form and striking burgundy-purple color. This ornamental grass features long, slender foliage that provides rich texture and contrast in garden beds and containers. From mid-summer through fall, it produces soft, crimson plumes that resemble fluffy bottlebrushes, giving it the characteristic “fountain” appearance.
Standard Height and Spread
The typical mature height of Purple Fountain Grass ranges between three and five feet. This measurement includes the arching flower plumes, which extend above the foliage. The plant establishes a fast, mounding, clump-forming growth habit, reaching its full size within a single growing season.
The horizontal spread of the clump usually measures between two and four feet wide, creating a rounded, vase-like silhouette. This width is often proportional to the height, contributing to the balanced, fountain-like shape.
Key Environmental Factors Dictating Size
To achieve its maximum height and spread, Purple Fountain Grass requires specific environmental conditions. Full sun, defined as a minimum of six hours of direct sunlight daily, is necessary for efficient photosynthesis and rapid growth. Insufficient light results in a smaller, lankier plant with less intense foliage color.
The soil must be well-drained, as the plant will not tolerate standing water around its roots. While it is adaptable to various soil types, poor drainage can stunt development and lead to root decline. Consistent moisture during the establishment phase is helpful. Once mature, the grass is moderately drought-tolerant, but extended dry periods may limit the overall size it attains.
Seasonal Pruning and Maximum Height
The maximum height noted on plant labels is the size the grass reaches within one growing cycle before dormancy or pruning. In colder climates, Purple Fountain Grass is typically grown as an annual because its roots cannot survive temperatures below approximately 20 degrees Fahrenheit. In these zones, the plant reaches its full three-to-five-foot height before dying back completely.
In warmer, mild-winter regions where it is grown as a perennial, seasonal pruning directly influences the plant’s size the following year. Gardeners cut the entire clump back heavily, often to a height of four to twelve inches, in late winter or early spring. This maintenance removes old, dormant foliage and encourages the production of new, colorful growth, allowing the grass to reach its full height again.