Muhly Grass (Muhlenbergia capillaris) is a popular perennial ornamental grass known for its low-maintenance nature and late-season color. It is best known for the airy, cloud-like plumes, which typically emerge in shades of pink or purple during the late summer and fall months. Understanding the plant’s full dimensions is helpful when planning its placement in a garden setting.
Mature Height and Spread
The size of Muhly Grass is described by two measurements: the height of its foliage clump and the overall height when in full bloom. The primary foliage, consisting of fine, wiry, dark green leaves, forms a dense, mounding clump. This basal foliage typically reaches 18 to 36 inches (1.5 to 3 feet) tall.
The width of the clump is often equal to or slightly greater than the foliage height, usually spreading between 2 and 4 feet wide. The mounding shape makes it suitable for mass plantings or borders. The overall height increases significantly once the distinctive, feathery flower plumes emerge in the autumn.
These plumes rise above the foliage, adding another foot or more to the total height. When fully extended, the grass reaches an overall height of 3 to 4 feet. Under optimal growing conditions, the mature size, including the plumes, can reach up to four feet tall and three feet wide.
Environmental Needs for Robust Growth
To achieve maximum size and abundant plume display, Muhly Grass requires specific environmental inputs. The most important factor for robust growth is direct sunlight. Planting the grass in a location that receives full sun (six or more hours of direct sunlight per day) is necessary for the best growth and flowering.
Insufficient light will cause the plant to grow weaker stems and produce fewer flower plumes. While the plant tolerates poor or sandy soils, the soil must be well-drained to prevent root issues. It is adaptable to various soil types, including sandy, loamy, and clay, provided water does not collect around the roots.
The plant is highly drought-tolerant once established, reflecting its native habitat. Consistent watering is important during the first full growing season to help the root system establish. Failure to provide adequate drainage or planting in standing water can lead to root rot, preventing the grass from reaching its mature dimensions.
Controlling Size Through Pruning and Division
Although Muhly Grass is a naturally well-behaved clumping grass, maintenance practices are necessary to manage its size and appearance over time. The primary method for size control is annual pruning, which removes old, dead foliage and prepares the plant for new growth. This cutback should occur in the late winter or early spring, before the new growth cycle begins.
The plant should be cut back to a height of 4 to 6 inches above the ground level. Pruning to this height prevents the accumulation of dead material, or thatch, which can inhibit new shoots and reduce the clump’s vigor. Cutting the grass back during the active growing season or late summer must be avoided, as this interferes with the production of the late-season plumes.
Another management technique is the division of mature clumps, which helps maintain size and prevents a dead center from forming. Ornamental grasses benefit from being divided every three to five years. This process involves digging up the dense, fibrous root ball and separating it into smaller sections for replanting. Dividing the clump rejuvenates the plant, ensuring it continues to grow with vigor.