Ornamental grasses haven't been so popular since the Victorian Age. Dozens of ornamental grasses are now available, and new forms are being added each year. The reasons for this astonishing rise in popularity appear to center around the practical, as well as the aesthetic merits of ornamental grasses. As the public becomes more environmentally aware, and learns more about low maintenance plants and sustainable landscapes, ornamental grasses that can tolerate extremes of drought and wetness are eagerly sought. Many ornamental grasses are also able to endure the repeated soil freezing and thawing typical of northeastern winters. Ornamental grasses are also a part of the growing popularity of water gardening, as transitional elements between dry land and water.

Ornamental grasses serve many functions in the landscape. Ornamental grass foliage catches the wind, adding a sense of motion to the landscape. The native prairies of the Midwest were often described as an inland sea. Tall grasses also rustle in the wind, adding sound as a new dimension to the landscape. In a border, grasses can be used as edging or background plants, while larger specimens can be accent plants or screens. Rhizome- and stolon-forming grasses stabilize banks or serve as ground cover. Diminutive species can be utilized in rock gardens. Combining grasses with woody or herbaceous perennial plants, such as shrub roses or Sedum 'Autumn Joy', help create a beautiful and enduring, low input, sustainable landscape. The dried foliage and flowers of many ornamental grasses are attractive and sway with the wind thoughout the cold winter months. Many are excellent for use in floral arrangements.

Culture:

Ornamental grasses, in both foliage and inflorescence (seed head), vary greatly in size, shape, color and texture. One of the largest ornamental grass collections in the Northeast may be viewed at the University of Rhode Island East Farm Agricultural Experiment Station in Kingston. Call (401) 874-5220 to schedule a visit. Mature plants range in height from 6 inches (blue sedge, Carex glauca) to 14+ feet (hardy pampas, Saccharum ravennae). Grass forms vary from low mounding to fountain shaped to tall vertical. Foliage color includes shades of green, yellow, blue, red, brown and variegated (green and white mixed). A number of grasses change in 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 (blade width 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 or grasslike plants tolerate wet soils, but more require a 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. Adequate organic matter will develop a soil with sufficient pore size to readily release water. The improved root zone will allow for maximum root expansion and water extraction from the soil. Improving the soil also will reduce irrigation frequency. Your investment in soil improvement will be returned in fewer maintenance problems and more attractive, longer-lived plants.

Ornamental grasses may be propagated from seed or division, and can be purchased from seed companies, mail-order firms and garden centers. Generally, the improved strains, which include most of the new varieties, will not come true from seed and must be propagated from divisions. Many grasses do not transplant or propagate well after midsummer because root growth slows dramatically. Container-grown plants may be transplanted into the landscape throughout the growing season.

Since the foliage portion of the plant should be cut down to the ground and removed each fall or spring, 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, therefore a soil test for deficiencies of these elements should be carried out periodically and recommendations followed. Do not over-fertilize ornamental grasses, as this can lead to lodging (falling over) and disease problems.

In contrast to other flowering perennials, ornamental grasses require minimum maintenance and most species are both insect and disease resistant. However, improperly sited plants may become diseased because of poor air movement, high nitrogen soils or inadequate light. As ornamental grasses becomes more common, pest problems may develop. At that point, cultivar selection will be more important.

A Few Cautions:

As with most plants, there are common myths or misunderstandings about the ornamental grasses. For example, many durable and hardy ornamental grasses growing in Rhode Island are mistakenly called Pampas grass. Cortaderia selloana, the only true Pampas grass, will not grow in Rhode Island. Ordering grasses under the name of Pampas grass will result in disappointment in this region.

Planting grasses whose dried foliage is to remain for the winter near combustibles such as a house or garage is not a wise practice. Dry grass foliage and flowers can be highly flammable. Remove foliage in the fall if a potential fire hazard is at all possible.

The first question to ask about a grass: is it rhizomatous (spreading by underground stems) or clump forming? Rhizomatous types make excellent ground covers, erosion control plants, and dense cover plantings that resist the invasion of weeds. The rhizomatous types spread at different rates laterally, some as much as twelve 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 a great deal of difficulties in managing the garden, and results in great satisfaction from this very desirable group of plants.

There are many grass or grasslike plants suitable as ornamentals, both native (ex. big bluestem, Andropogon gerardii) and exotic (ex. fountaingrass, Pennisetum alopecuroides 'Hameln'). Native grasses were members of the local flora before European settlers arrived. Exotic grasses are introduced plants from other states or countries. Some have escaped cultivation and become part of the local flora. Some grasses, such as little bluestem, annual pennisetums, and early flowering Miscanthus, can reseed in your garden or spread to wetland areas where they can become real pests. New grass species and cultivars should be evaluated for invasiveness before being grown for sale.

Ornamental Grass Types:

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

Fescue: This cool season, clump-forming grass 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 showiest group of warm season, clump-forming grasses, it has very showy flowers. A large group of grasses with considerable variability in height, blade width, etc. Select cultivars carefully to insure adequate hardiness and adaptation to your 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 popular.

Fountaingrass: Most members are warm season, clump forming grasses. Some may become weedy, especially south of Rhode Island. Both annual and perennial cultivars are valuable in the landscape. Flowers are showy and are foxtail-like in their appearance.

Dr. Brian Maynard, Sustainable Landscapes Program Department of Plant Sciences, URI, Kingston, RI