Ornamental grasses offer dynamic texture and movement, providing interest long after many flowering plants have faded. Like most perennials, these plants require periodic maintenance, referred to as rejuvenation, to restore their aesthetic appeal and vigor. This process addresses the natural decline that occurs as the plants age, particularly in their dense root structures. Understanding the plant’s life cycle and applying specific techniques ensures the grasses maintain a healthy and robust appearance for many years.
Assessing the Need and Timing for Rejuvenation
Rejuvenation becomes visually apparent when clumping grasses look less full and their foliage begins to flop over. A clear sign of aging is the development of a “doughnut shape,” where the center of the clump has died out, leaving a hollow core. This dead center indicates that the dense root system has become too congested to sustain life in the middle, reducing overall plant health.
The timing for major maintenance is important and generally falls in late winter or very early spring, just before the plant breaks dormancy. Performing these tasks during this window minimizes stress and provides the entire growing season for recovery. Cool-season grasses should be addressed as soon as the snow melts, as they begin growth earlier. Warm-season grasses can be tackled slightly later, but always before active growth begins.
The Essential Step of Cutting Back Old Foliage
Cutting back last season’s growth annually is a simple maintenance task essential for rejuvenating almost all ornamental grasses. This step provides a clean slate for the new season, preventing old, brown foliage from mingling with fresh green blades. For large clumps, gather the dead foliage into a column and secure it tightly with rope or a bungee cord to make the process easier.
The height of the cut depends on the grass type, differentiating between deciduous and evergreen varieties. Deciduous grasses, which turn completely brown in winter, should be cut back severely, leaving a stubble of about four to six inches above the ground. For very tall warm-season grasses like Miscanthus, use sharp shears, a hedge trimmer, or an electric saw to cut through dense root crowns.
Evergreen grasses and grass-like plants, such as certain sedges (Carex), require a gentler approach since they do not go fully dormant. These plants should not be cut back hard, as this can damage the crown and lead to rot. Instead, rejuvenation involves using fingers or a rake to manually comb out dead leaves, brown tips, and matted debris from the base.
Dividing Overgrown Clumping Grasses
Division is the most effective technique for rejuvenating clumping grasses that have developed a dead center or become too large. This process is reserved for clumping varieties, as running grasses are managed differently due to their spreading rhizomes. To begin, cut the foliage back to a manageable height of four to six inches, then water the area a day or two prior to soften the soil.
The entire root ball must be dug up, which can be an arduous task for mature specimens with tough, fibrous roots. Once the clump is out of the ground, separate and discard the dead, woody core, as it will not regenerate growth. The vigorous, living material is typically found in a ring around the outer edge of the clump.
Dividing the dense root mass often requires heavy-duty tools beyond standard gardening implements. A sharp spade, an axe, a pruning saw, or even a chainsaw are commonly used to slice through the tough, entangled roots. Cut the viable outer ring into smaller sections, ensuring each new division retains a healthy mass of roots and dormant buds. These rejuvenated sections are then ready for replanting back into the original location or elsewhere.
Post-Rejuvenation Maintenance and Care
Immediate and consistent watering is essential following any division or replanting to help the newly cut roots establish quickly. Keep the soil around the fresh divisions consistently moist for several weeks, allowing the roots to anchor themselves before the heat of the growing season. This initial attention is important because the grass has lost a significant portion of its root system during the process.
Fertilization should be handled with restraint, as ornamental grasses thrive on low fertility and can become weak or “floppy” if overfed. If the soil is poor, apply a single application of a balanced, slow-release fertilizer in early spring as new growth begins. Use a formula where the nitrogen content is not excessively high, such as a 10-10-10 ratio, to support structure without causing unstable leaf growth.
Applying a layer of organic mulch, such as shredded bark or compost, around the base of the plants is beneficial. A layer of up to three inches helps regulate soil temperature, retain moisture, and slowly contribute organic matter as the plant recovers. This final step ensures the rejuvenated grass has optimal conditions to produce healthy, vibrant new foliage.