Pennisetum setaceum 'Rubrum' or purple fountain grass is a very attractive ornamental grass. It is sold as a perennial in many nurseries, but it is not winter hardy. It should be a considered tropical plant and grown as an annual in areas that have cold winters. In mild winter areas, purple fountain grass will survive the winter outdoors. Grasses like full sun and well-drained soil. If your plant is dying, it is either planted in an area that got too cold in winter, or it is not getting enough sun, or the right amount of water.
Prune back the grass plant leaving a little green growth of if there is some.
Dig carefully around the roots and remove the plant from the soil. Try not to break the thicker roots as you loosen the soil.
Look for healthy roots. If the root ball is dry and the roots are shallow and thread-like, the fountain grass is not getting enough water and the soil is too heavy for the roots to spread.
Gently remove loose soil from the roots and place the plant in a container with at least 3 inches of potting soil in the bottom. Water thoroughly and allow the pot to drain.
Fill the container with soil, water again and place your fountain grass in a sunny location. Water regularly and watch for new growth.