Elegant with its vase-like shape and drooping seedheads, purple fountain grass (Pennisetum setaceum and cultivars) is among the most popular of ornamental grasses for the garden and containers. Although a marginally hardy plant, surviving winters in USDA plant hardiness zones 8 through 11, it will reseed itself and sprout back in the spring in colder regions after frost danger has passed. In areas where it may survive the cold winter, where temperatures dip no lower than 5 degrees Fahrenheit, retaining the foliage and planting it well before winter improves its chances.
Plant purple fountain grass early in the growing season. Providing ample time for a newly transplanted grass to establish before the winter improves its chances of survival. However, in cold winter regions, it still will not survive prolonged subfreezing soil temperatures.
Moisten the soil around the fountain grass leading into autumn. Although quite drought-tolerant, a grass can have reduce vigor and be stressed if water is severely lacking leading into the autumn. The soil should never be soggy.
Place a thick, loose layer of mulch around the base of the grass after the killing autumn frost. A 4- to 6-inch covering of oak leaves or straw can shield the dormant roots of the grass from fluctuating winter temperatures between day and night and shield it from bitter cold.
Retain the frost-dried foliage and seed head plumes on the grass clump across the winter. This is particularly true in areas where this grass species is marginally hardy to the winter, such as in chillier parts of Zone 7.