Ornamental grasses are perennial plants prized for their fine texture, dramatic structure, and movement in the landscape. These versatile plants offer year-round interest, but to ensure they remain healthy and vigorous, an annual cutback is necessary. Pruning removes the old, spent foliage and stems, clearing the way for new growth to emerge unhindered each spring. Skipping this maintenance step can lead to an unsightly accumulation of dead material. This accumulation prevents proper air circulation and reduces the plant’s overall vitality.
Determining the Right Time to Prune
The correct timing for pruning ornamental grass depends on its specific growth habit, dividing plants into deciduous and evergreen/semi-evergreen categories. Most pruning is best performed in late winter or early spring, before new green shoots appear from the crown. This timing allows gardeners to enjoy the dried foliage and seed heads, which provide winter interest, protection for the plant crown, and habitat for wildlife.
For most deciduous varieties, waiting until the threat of hard frost has passed is important. Pruning too early can expose the delicate crown to freezing temperatures, while pruning too late risks cutting into tender new growth. The appearance of new growth is the best indicator that it is time to perform the cutback. Though species like warm-season Miscanthus and cool-season Festuca have different schedules, the principle of pruning before or just as new growth begins remains constant.
Cutting Back Deciduous Grasses
Deciduous grasses, which turn brown and dormant over winter, require an aggressive cutback to ground level to rejuvenate the plant. This group includes popular varieties like switchgrass (Panicum), fountain grass (Pennisetum), and maiden grass (Miscanthus). The goal is to remove all the old, dead material so the new season’s foliage can develop unhindered.
Before cutting, secure the clump with twine, rope, or a bungee cord. This keeps the cut foliage contained, turning debris into a single, manageable bundle for disposal. Always wear sturdy gloves and long sleeves, as the edges of some grass blades can be sharp and cause skin irritation.
Use sharp, clean tools like long-handled shears, pruning loppers, or electric hedge trimmers for larger clumps. Make the cut across the bundled foliage 4 to 6 inches above the soil line. Leaving a few inches of old stubble protects the crown from moisture and rot while providing a visual marker of the plant’s location. Clear any remaining loose or matted debris from the crown to ensure good air circulation.
Maintaining Evergreen and Semi-Evergreen Varieties
Evergreen and semi-evergreen grasses, such as Carex sedges and Blue Fescue (Festuca glauca), maintain much of their foliage throughout the year and should never be subjected to a hard cutback. These varieties store energy in their leaves, and removing too much green material can severely stress or kill the plant. Maintenance focuses on selective cleanup to remove only dead or damaged blades.
Use gloved hands or a garden rake to gently comb through the clump, pulling out the buff-colored, dead material accumulated near the base. This “combing” technique removes debris and aerates the plant, encouraging new growth without compromising the plant’s structure. If the grass appears shaggy or has brown tips, perform a light trim of only the damaged ends, avoiding cutting more than one-third of the overall foliage height.
If a plant is damaged by harsh winter weather, a more aggressive rejuvenation prune can be performed. This must be done to a height that leaves a significant portion of the green foliage intact. This reduction should be done infrequently, perhaps every two to three years, allowing the plant time to fully recover its energy reserves.