The rich, dark color of purple ornamental grasses makes them highly sought-after in modern landscaping, providing dramatic contrast and texture. “Purple grass” is an umbrella term, leading many gardeners to wonder if their plant will return year after year. Whether a purple grass is a perennial—meaning it regrows naturally each spring—depends entirely on the specific species and local climate conditions. To successfully grow and maintain this foliage, a gardener must first identify the plant and understand how cold temperatures affect its survival.
Identifying the Different Purple Grasses
The plants commonly sold as “purple grass” primarily belong to a few different genera, each with distinct characteristics and life cycles. The most popular variety is Purple Fountain Grass (Pennisetum setaceum ‘Rubrum’). This grass forms a graceful, arching clump of maroon-red to burgundy foliage, topped with soft, bottlebrush-like plumes that persist through fall.
Another dark-leaved plant is Purple Millet, often a cultivar of Pennisetum glaucum, such as ‘Purple Majesty’. This plant is distinguished by its upright, rigid growth habit and thick, cylindrical seed heads. A third major group includes purple-hued varieties of Switchgrass (Panicum virgatum), like ‘Purple Tears’, which exhibit a narrow, upright form and airy plumes that mature to a purplish seed head.
Perennial Status Based on Hardiness Zones
A perennial plant lives for more than two years, surviving winter dormancy to reemerge in spring without replanting. The ability of a purple grass to behave as a true perennial is determined by the USDA Plant Hardiness Zone system, which maps average minimum winter temperatures. Understanding the distinction between a perennial, an annual, and a tender perennial is crucial for these ornamental varieties.
Purple Fountain Grass (Pennisetum setaceum ‘Rubrum’) is classified as a tender perennial. It reliably survives winter only in the warmest zones, specifically USDA Zones 9 through 11. In cooler regions (Zone 8 and below), the plant is not cold-hardy enough to withstand freezing temperatures and is treated as a seasonal annual. While protection may be attempted in Zone 8, its return is not guaranteed.
Switchgrass (Panicum virgatum) cultivars are native North American warm-season grasses that are true perennials over a much broader range. Varieties like ‘Purple Tears’ are reliably hardy down to USDA Zone 4. Their root systems can survive extreme cold temperatures, allowing the plant to regrow from the base each spring.
Purple Millet (Pennisetum glaucum) is typically grown as a warm-season annual in nearly all parts of the United States. It completes its life cycle in a single growing season and will not survive frost or cold temperatures. Since it requires replanting yearly, the question of overwintering millet is irrelevant for most gardeners.
Essential Care and Maintenance
All purple grasses thrive in similar conditions, regardless of their perennial status. They require full sun for at least six to eight hours daily to ensure the darkest foliage color. These plants prefer well-drained soil, as wet conditions, especially during colder months, can lead to root rot. Once established, many ornamental grasses, including Purple Fountain Grass and Switchgrass, are moderately drought-tolerant.
For true perennial varieties like Switchgrass, maintenance involves cutting the entire plant back to about four inches above the ground. This pruning should be done in late winter or very early spring before new growth begins, clearing the old, dormant foliage. If treating a tender perennial like Purple Fountain Grass as an annual, simply remove the dead plant after the first hard frost. To save a potted tender perennial, bring it indoors before frost and keep it in a cool, bright location with minimal watering throughout the winter.