This NebGuide discusses the selection of and care for ornamental grasses.
John C. Fech, Extension Educator
Dale T. Lindgren, Extension Specialist
Anne M. Streich, Extension Educator
Kim A. Todd, Extension Specialist
Grasses always have been a primary component of prairies. However, Great Plains gardeners are learning to appreciate their aesthetic qualities and seasonal interest in landscapes as ornamentals. Many ornamental grasses tolerate drought, low fertility, fluctuating winter temperatures and a variety of soil conditions. They also are resistant to many insect pests and most diseases. Because of these characteristics, they are useful to gardeners interested in low input landscapes.
True grasses belong to a specific plant family. However, other grasslike plants, such as sedges and rushes, belong to other plant families yet resemble grasses and should be considered when choosing plants for landscape purposes. They are typically used in wetland landscapes as many tolerate moist soil and shady conditions, yet some prefer dryland sites.
Ornamental grasses vary in size, form, color and texture. Mature plants range in height from 6 inches to over 10 feet. Plant forms vary from low mounds to upright to arching. Foliage and inflorescence (flower) colors include green, gold, tan, brown, orange, red, burgundy, silver, white and variegated. Many grasses also exhibit attractive fall colors. Foliage texture varies from fine to bold. Specific attributes of some grasses recommended for Nebraska are listed in Table I.
Ornamental grasses can serve many functions in the landscape. They can be used as screens, backdrops, specimens, masses, groundcovers or edgers. They can provide scale transitions between larger woody landscape plants and smaller herbaceous plants, visually tying them together and connecting one set of plants to another. Ornamental grasses can be used in either formal or naturalized landscapes. Because the leaves are easily blown around in the wind, rustling sounds and gentle motions are created; they also provide various degrees of texture, which is an important, yet often overlooked feature of a landscape. In addition, ornamental grasses provide valuable wildlife cover and can serve as a food source.
Unlike herbaceous perennials, many ornamental grasses have foliage that remains attractive throughout the winter months. They serve to complement the effectiveness of other plants with cold weather interest such as bergenia, English ivy and Japanese spurge. Some also have persistent seedheads that add interest to the winter landscape. Many also are valuable for use in fresh and dried floral arrangements.
To prepare a site for ornamental grasses, eliminate all perennial and annual weeds. Because most grasses require a well drained soil, they will benefit from the incorporation of organic matter into the root zone. Addition of compost to clay soils will improve drainage while incorporation of compost in sandy soils will increase water and nutrient holding capacity. The improved root zone area will allow for maximum root expansion and water extraction from the soil. Time and effort spent in soil improvement is a good long-term investment.
Most ornamental grasses are available in containers. This allows for ease in planting and an extended planting season. Annual grasses should be planted in the spring after the last frost date. Perennial grasses can be planted anytime during the growing season, prior to mid September, as long as adequate follow up care can be provided. Some ornamental grasses can be seeded. The appropriate time for seeding warm and cool season grasses varies from east to west in Nebraska. Check with your local extension office or nursery professional for specific information.
Most ornamental grasses require full sun, although some tolerate part shade. Ornamental grasses may be selected for a variety of soil conditions, including differences in soil texture and pH. Some tolerate degraded or damaged soils, while some do not. Many ornamental grasses are drought tolerant and tend to flop when over-watered. For specific information on the site preferences of each grass, see Table I.
Before planting in a new site, test the soil. The soil test will determine the organic matter percentage, available phosphorous and potassium levels, the pH and the soluble salts content. Adjust these as needed before you plant and then retest every four to five years. If the soil lacks sufficient nutrients, incorporate them into the root zone before planting. They will not move into the root zone adequately if applied only to the soil surface. Micronutrient deficiencies vary geographically. Check with local county extension staff for specific guidelines in your area.
Between soil tests, use foliar appearance as a guide to nutritional requirements. An off-green leaf blade may be a symptom of poor soil fertility, low soil oxygen, inadequate drainage or excess watering. Because most ornamental grasses have low nutritional requirements, fertilize them only when the leaf color indicates a need, and other possible causes of poor growth such as inadequate iron levels or high pH soils have been eliminated.
Ornamental grasses require supplemental irrigation until they develop a mature root system. Once established, mature plants typically have deep root systems and can extract sufficient water from the soil to maintain growth during drought conditions. If irrigation is necessary, drip or surface irrigation should be used to reduce the incidence of foliar diseases. Many drought tolerant grasses will not grow well if over-watered. Once ornamental grasses mature, the amount and frequency of water required will vary with grass species and characteristics of the site including soil type, sun exposure and wind.
The most effective method of controlling weeds near ornamental grasses is to start with a weed-free site. Once they are established, applying a 2 to 3 inch layer of wood chips and/or a pre-emergence herbicide in the spring can control many grassy and broadleaf weeds. Weeds that are already growing can be controlled by hand pulling, hoeing or with the use of post-emergence herbicides. When using post emergence herbicides, care must be taken to avoid herbicide contact with desirable plants. With all herbicide applications, read and follow label directions.
Allowing foliage to remain throughout the winter helps protect the crown from drying out and provides seasonal interest and wildlife habitat. When winter storms and other landscape care activities cause the stems to fall over, remove them to maintain aesthetic quality and avoid damage by small animals. Many gardeners enjoy experimenting with grass species and cultivars that have not proven to be completely winter hardy (ie. Japanese bloodgrass). After the soil has frozen in the late fall, cover these plants with a coarse wood chip mulch, held in place with a device such as a rose collar.
Ornamental grasses are more attractive when dead foliage is not interspersed with living tissues. Before new growth begins, remove the previous years foliage to within a few inches of the ground or as close to the crown as possible. Cool season grasses, such as feather reedgrass and tufted hairgrass, will resume growth earlier than warm season grasses like maidengrass and most natives. A hand clipper, mechanical weed whip or other power equipment can be used to remove old growth. Grasses will begin growing earlier if dead foliage is removed in later winter.
The need for plant division depends on the growth rate, spacing requirements and visual appearance. Some ornamental grasses can remain in place for many years without needing division. If the center of the ornamental grass clump shows little or no growth, the plant should be dug up and divided. Remove the dead center clump, divide the actively growing outer edge into smaller pieces and replant. Spring is the best time to divide ornamental grasses, when the stems are 4 to 7 inches long or shorter.
The authors would like to recognize contributions made by co-author Don Steineger in the first edition of this publication.
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Issued January 2007