Why Ornamental Grasses?
Judy Ziemba, State Horticulture Chairman

The popularity of many plant families fluctuates and one, which has enjoyed an increased use in gardens in the past few years, is collectively called Ornamental Grasses. When gardeners begin to choose grass-like plants they may also include members of the sedge, rush and cattail families. It might be of interest to review the characteristics of these plants so the thoughtful gardener might successfully add their seasonal textures and colors in a garden.

Grasses can be divided in to clump growing or spreading varieties. It is important to choose a site very carefully for a spreading type, though they are great for stabilizing slopes or planting in completely confined areas. There are stories of rhizomes of some bamboos running long distances even under pavement and through asphalt. Lawn grasses are great for spreading and filling an area but spreading ornamentals become pests if not carefully sited.

Grasses can also be divided into the cool season varieties and the warm season varieties. The cool season types generally grow best in early spring and develop foliage and flower before the heat and dryness of summer slows their growth. They recover in the cooler and rainy autumn. Some varieties to grow are feather reed grass (Calamagrostis varieties) and blue fescues. Other cool season grasses which grow in Illinois include the Indian rice grass (Oryzopsis hymenoides), Blue oat grass (Helictotrichon sempervirens), June grass (Koeleria macrantha or K. cristata), silky threadgrass (Nassella tenuissima) and for moist or wet areas variegated bulbous oat grass (Arrhenatherum elatius bulbosum 'Variegatum'). The trick is to minimize dormancy the summer heat and drought causes. The variety of Calamagrostis 'Karl Foerster' does a fine job. With a partially shadied area and supplemental water, many of the cool season grasses remain presentable until the cool weather revives them.

Warm season grasses love the hot summers. They usually are slow starting in spring but once the heat arrives, they make up for lost time and by autumn have wonderful flowering plumes. When the growing season ends, our reward is the beautiful fall colors and graceful show of winter shapes and shadows. Some good examples of warm season grasses are the pampas grasses (Cortaderia sp.), Miscanthus species, and fountain grasses (Pennisetum sp.) Our native prairie grasses like little and big bluestem and switchgrass also are warm season grasses.

Generally the culture of both types of grasses requires full sun, any soil, and no fertilization. There are few diseases or insects to cause problems and their ability to handle dry hot sites is well known. Division of grasses should be made during their active growing times. This means cool season varieties can be divided in spring or fall and warm season grasses can be separated in late spring or early summer. This allows the new plants to become established while actively growing. The only maintenance required is to cut the stems (culms) back before the new shoots appear. Burning is the age-old method of cleaning out the old stems but not recommended unless great care is taken and certainly not near shrubs, trees, conifers or buildings.

Sedges (Carex sp.) are grass-like plants that may have unusual colors and forms and prefer moist areas. They are useful planted near ponds, planted in shady areas or can be cultivated in containers. Be sure to check the growing zone to be successful with these mophead types of plants. Rush family members (Juncus sp.) also prefer damp or wet places and have round stems and small flowers. Most are clump forming but some have rhizomes and/or reseed, requiring some vigilance to contain them. The cattail family (Typha sp.) has a miniature variety (T. minima) that can be grown in small ponds or containers but the larger species are quite invasive.

In addition to their low maintenance, hardiness, pest & disease resistance and ease of propagation, ornamental grasses should be considered for their near deer proof foliage, their fast growth for privacy screens and their use as specimen plants. The multi season display along with movement and sound and the abundance of fresh and dried flower arrangement materials, make them pleasant additions to any garden.

For more details and pictures about specific varieties, check web sites: www.urbanext.uiuc.edu/grasses/ , www.ext.colostate.edu or other state extension service web sites. Some nursery sites also have detailed information.