Answer: Ornamental grasses send up blooming stems in the late summer and the blooms last in good condition well into the winter. Some gardeners like the look and leave the plants as is until early spring. Other gardeners find they look untidy and so prefer to cut them back earlier.
You can cut them back any time after hard frosts have turned them brown. The latest you would want to do wait is about when the crocus bloom in the spring, the reason being you could damage the new growth if you wait to long to cut off the old dried material. In other words, you can cut them back any time from late fall to early spring.
Cut them back as far as you can manage, typically a large grass clump might be cut straight across at about six to twelve inches above the ground. I use an electric hedge trimmer to cut mine back but anything from a hand pruner to a chainsaw will do the job.
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