Purple Fountain Grass is not reliably hardy in zone 8. You may need to protect them during winter.

Muhly should do fine for you. They don't need any compost at any time, and could benefit from additional water now and then, depending upon their placement and your rainfall.

Thanks, Donn. Actually, the fountain grass is in protected areas. Just wondering why I have such trouble with grasses. Maybe I'm not watering them enough. We did have a dry winter.

By protecting it through winter, I meant bringing it inside in pots. It's technically rated for zone 9 and above, and I've heard of problems with it in zone 9. Most folks treat it as an annual, since it grows pretty fast and adds great accent to the garden.