Nursery Market Report: May 2001, Plant Primer: Ornamental Grasses 101

The reasons for their surge in popularity center on practical, as well as aesthetic, merits. Ornamental grasses can tolerate extreme drought and wetness, and they can endure the repeated soil freezing and thawing typical of Northeast and Midwest winters. At the same time, these grasses create several layers of interest in the landscape. When foliage catches the wind, it adds a sense of motion and sound, and in winter, dried flowers are eye catching.

Beyond aesthetics, these grasses have many practical uses. In landscape borders, they can be used as edging or background plants, while larger specimens can be accent plants or screens.

Rhizome- and stolon-forming grasses can stabilize banks or serve as ground covers, and diminutive species can be used in rock gardens. Also, combining grasses with woody or herbaceous perennial plants, such as shrub roses or Sedum ‘Autumn Joy,’ help create beautiful and enduring sustainable landscapes.

CULTURE. Ornamental grasses, in both foliage and inflorescence (seed head), vary greatly in size, shape, color and texture. Mature plants range in height from 6 inches for blue sedge to 14 or more feet for hardy pampas. Grass forms vary from low mounding or fountain shaped to tall and vertical. Foliage colors include shades of green, yellow, blue, red, brown and variegated green and white. Also, a number of grasses change foliage color in the fall to displays of straw yellow, orange, red or purple, providing a wealth of choices. Foliage texture varies from fine to coarse, with blade widths from 1/8 to 1 inch. The inflorescence also varies in size and color and may change color in the fall, as well.

Although a few grasses tolerate shade, most require full sun. Some grasses tolerate wet soils, but most require well-drained soil. To become drought and pest resistant, plants require a suitable root zone. In compacted soils, even the root systems of the most drought-tolerant plants will not develop.

Incorporate organic matter into the root zone to improve water-holding capacity and oxygen levels. The improved root zone will allow for maximum root expansion and water extraction from the soil.

In handling maintenance, foliage should be cut down to the ground and removed each fall or spring, and some fertilization is required to compensate for nutrient loss. A 10-10-10 fertilizer may be applied at a rate of 1 pound per 100 square feet. A good deal of calcium and magnesium is lost when removing foliage, so a soil test for deficiencies of these elements should be carried out periodically and recommendations followed.

A FEW CAUTIONS. Planting grasses with dried foliage that will remain for the winter near combustibles such as a house or garage is not wise. Dry grass foliage and flowers can be highly flammable, so remove foliage in the fall to avoid fire hazards.

Another point to consider is whether the grass is rhizomatous - spreading by underground stems - or clump forming. Rhizomatous types make excellent ground covers, erosion control plants and dense cover plantings that resist weed invasion. The rhizomatous types spread at different rates laterally, some as much as 12 or more feet a year, and may be invasive. The clump-formers simply increase in circumference, requiring division every three or four years. Distinguishing between the two types and locating them in proper sites will prevent difficulties in managing the landscape.

Yet another important consideration is whether the ornamental grass is native or exotic. Native grasses were members of the local flora before European settlers arrived, while exotic grasses were introduced from other states or countries. Some have escaped cultivation and become part of the local flora. Other grasses, such as little bluestem, annual pennisetums and the early-flowering Miscanthus, can reseed in the garden or spread to wetland areas, where they can become real pests. New grass species and cultivars should be evaluated for invasiveness before they are installed in the landscape.

ORNAMENTAL GRASS TYPES. The most popular groups of ornamental grasses are Festuca (fescue), Miscanthus, Panicum (switchgrass) and Pennisetum (fountaingrass).

Fescue. Fescue is a cool-season, clump-forming grass that requires protection from the hot afternoon sun. Blue foliage forms are the most popular.

Division in the early spring is often required to restore vigor. Regular fertilization may benefit this group.

Miscanthus. Considered the flashiest group of warm-season, clump-forming grasses, it has very showy flowers. Miscanthus is a large group of grasses with considerable variability in height and blade width. Select cultivars carefully to ensure adequate hardiness and adaptation to the landscape site.

Switchgrass. This native, warm-season, clump-forming group is becoming more popular as new cultivars become available. Cultivars with red fall color and blue-foliaged, upright cultivars are currently trendy.

Fountaingrass. Most are warm-season, clump-forming grasses. Some may become weedy. Both annual and perennial cultivars are valuable in the landscape. Flowers are showy and foxtail-like in appearance.