Most grasses benefit by being cut back, usually just before new growth begins in the spring.
Use hedgeshears that have been sharpened for the season, and wear gloves to protest your hands from the sharp edges of the grasses. Some perennial-type grasses might require a chain saw to divide them. After cutting the plants back, mulch them to retain moisture, improve the soil and suppress weeds. Spring also is a great time to plant new ornamental grasses. Remember that some grasses grow best in warm weather while others like it cooler.