Ornamental grasses are non-turf varieties of grass and grass-like plants cultivated for their aesthetic appeal in landscaping, rather than for utility like lawns or crops. They are popular in modern garden design due to the dynamic texture and structural form they introduce. These plants offer year-round visual interest and are praised for their low-maintenance nature and ability to thrive once established. Their versatility allows them to serve multiple roles, from groundcovers to large architectural statements.
Defining Characteristics and Structure
Ornamental grasses are distinguished by their physical attributes. Foliage generally consists of long, narrow blades that can display a variety of colors, including greens, blues, silvers, golds, and even deep reds and purples. These leaves may have a fine, hair-like texture or a coarser, broader feel, and they typically form in dense clumps with an upright or gracefully arching habit.
The inflorescence, commonly referred to as plumes or seed heads, emerges in summer or fall. These structures can be feathery, spiky, or airy and often appear above the main foliage, creating a striking visual contrast. The plumes change color and texture as they mature, persisting well into the winter months to provide continued interest in the dormant landscape.
While the term “ornamental grass” strictly refers to plants in the true grass family (Poaceae), the category is often broadened to include grass-like plants like sedges (Cyperaceae) and rushes (Juncaceae). True grasses possess hollow, cylindrical stems with solid joints, or nodes. Sedges, in contrast, typically feature solid, triangular stems, while rushes have solid, round stems and are usually found in moist or wet conditions.
Classification by Growth Habit
Ornamental grasses are primarily categorized by their seasonal growth patterns, which directly influences their maintenance schedule. This classification separates them into two main groups: warm-season and cool-season grasses. This distinction is important for proper care and for knowing when the plants will look their best.
Warm-season grasses begin active growth later in the year, typically when soil temperatures rise above 60 to 65°F in late spring or early summer. They thrive in summer heat, with vigorous growth occurring when temperatures are between 80 and 95°F. These grasses, such as Maiden Grass (Miscanthus sinensis) and Fountain Grass (Pennisetum species), usually turn tan or brown and go dormant after the first hard frost, but they hold their shape and plumes well into the winter.
Cool-season grasses begin growing early in the spring when temperatures are mild, generally between 60 and 75°F. Their growth slows or stops entirely during the hottest part of the summer, and they may go dormant in intense heat or drought. Feather Reed Grass (Calamagrostis) and Blue Fescue (Festuca glauca) are examples of this type, which often remain semi-evergreen or green for much of the winter. They often experience a second flush of growth as temperatures cool again in the fall.
Landscape Function and Aesthetic Impact
Ornamental grasses introduce dynamic elements that static plants cannot provide. The slender foliage and airy plumes catch the slightest breeze, creating a sense of natural movement and rhythm in the landscape. Taller varieties also add an auditory element, producing a soft, rustling sound as their leaves brush against each other.
The architectural structure of many grasses provides a strong vertical or mounding form that contrasts effectively with the shapes of other garden plants. Tall-growing selections, such as Switchgrass (Panicum virgatum), can be used strategically to create living screens for privacy or to define outdoor “rooms.” This structural presence is maintained throughout the dormant season, providing texture and visual weight in the winter garden.
Grasses are also used to manipulate light and texture within a planting scheme. The fine texture of their foliage can soften the appearance of hardscaping or be paired with broad-leaved plants to create visual depth and contrast. When backlit by the sun, the feathery plumes and seed heads of grasses like Pink Muhly Grass (Muhlenbergia capillaris) become luminous, offering a captivating glow in the garden.
Essential Care and Maintenance
Ornamental grasses are generally low-maintenance plants, requiring little to no fertilizer and demonstrating good drought tolerance once established. The primary care task is determining the correct timing for cutting back the dormant foliage, which depends entirely on the warm-season or cool-season classification. Warm-season grasses should be cut back hard, to within a few inches of the ground, in late winter or early spring before new growth begins. Cutting back at this time allows the old foliage to protect the crown through the winter and ensures the new shoots are not damaged.
Cool-season grasses, which often remain semi-evergreen, should not be cut back to the ground. Instead, they only need a light trimming to remove dead or damaged leaf tips. This is usually done by removing no more than one-third of the plant’s height in late winter or early spring. This lighter pruning prevents the removal of the plant’s evergreen structure.
Division is a necessary maintenance task, especially for clump-forming varieties, and should be performed when the plant is actively growing to ensure quick recovery. Warm-season grasses are best divided in the spring or early summer, just as new growth emerges. Cool-season grasses are typically divided in the early spring or in the fall to avoid transplanting stress during summer heat. Division, generally performed every three to five years, maintains the plant’s vigor and prevents the center of the clump from dying out.