Ornamental grasses tend to require very little maintenance pruning save the removal of damage, flower heads or seed heads, if you desire. Ornamental grasses come in two main forms: rhizomatous and spreading, or clump forming. Spreading forms use runners to creep across distances and often need to be contained to an area via pruning. Clumping grasses are commonly appreciated for their fountain-like natural form and rarely require pruning for shaping purposes. In climates where ornamental grasses do not overwinter in an attractive form, they can be sheared down entirely in the fall or winter making way for spring growth.
Conduct maintenance pruning on your ornamental grass regularly as needed throughout the growing season. Inspect the grass each time you water to look for signs of damage or disease. Prune away any dying or browning foliage and stems with your secateurs and discard. Remove damaged foliage from clumping grasses down to the crown to maintain the growth form. Spreading grasses can be cut down to the soil as necessary to remove the damage.
Hard-prune your ornamental grass once a year or as needed to control the shape and size of the stand. Hard-prune the grass to thin the interior of the stand and shape the growing perimeter of the grass. Prune the tops of ornamental grasses judiciously as over-pruning destroys the natural form of the plant.
Shear down your ornamental grass in the late fall or winter in climates where the top foliage does not survive the winter or remain attractive in its dried state. Many clump forming grasses dry out and remain upright in their natural form over the winter with the bleached clumps providing interest in the garden. Shear the grass down in the early fall before the seed heads mature and disperse their contents if you do not want your ornamental grass to self-sow.