Answer: It isn't necessary to trim back ornamental grasses unless the blades turn brown and wither away. If that happens, cut them off at ground level, or, as in the case of blue fescue, pull the brown blades away from the healthy blades.
In temperate climates ornamental grasses can grow all year long, but some blades will eventually need to be cut back. Use your own judgement, cutting back only those that are unattractive.
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