About Purple Fountain Grass. While purple fountain grass is known as a perennial, it is actually considered a tender perennial. This ornamental grass cannot survive cold winters and is hardy only in USDA Plant Hardiness Zones 9 and warmer (though in Zones 7-8 it can sometimes reappear given adequate winter protection).ake Care of Purple Fountain Grass. Caring for purple fountain grass is also easy. The plant is drought tolerant so watering sufficiently every week or two should be adequate. Although nor required, you can give it an annual feeding with a slow-release, balanced fertilizer in spring to help stimulate new growth.