Grasses with Gusto

Grass has always been a part of the landscape. As a groundcover, it provides excellent transition elements between areas of the garden. It also makes a great place to play ball, have a picnic or just walk through barefoot. Since the 1970s, grass has taken on another roll, that of being one of the “stars” in an ornamental role. Ornamental grasses have become popular with landscape designers for their interest, versatility, compatibility with other perennials and shrubs, adaptability and rapid growth.

FINDING YOUR TYPE

Ornamental grasses range from low-growing groundcovers to tall towering plants. The foliage color can run from green to variegated yellow or white to red with textures varying from fine to heavy and coarse. These grasses can be used as specimen or accent plants or as the entire focus of a planting, creating large drifts of texture. They are also useful in containers with other annuals or perennials.

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Grasses can be selected to fit most any setting. Most grasses are best grown in full sun and well-drained soils. There are, however, several grasses that can provide interest in shady spots as well as wet soils that might be found along water features.

The term ornamental grass can include any number of plants that are either true grasses or grass look-alikes. Many of these grass look-alikes are, in fact, part of the sedge family or rush family. Even though not true grasses, they are a useful group of plants that often find their way into gardens under the title of ornamental grass. Bamboo is another true grass that has unique properties because it is one of the woody grasses. In some cases it can be useful in the landscape, but you have to use it with some caution.

When selecting ornamental grasses for the landscape, the overriding features of color, texture and form take center stage. There are, however, other characteristics you should note before introducing these plants into the landscape. By doing a little research and understanding what certain terms mean, the plants can be put to best use and you can often avoid disappointment, frustration and perhaps even the chance of using the wrong grass in the wrong place, resulting in a horticultural nightmare once it gets going.

You can select grasses based upon growth habit and temperature preferences. Two types of growth habits characterize ornamental grasses: running or clumping.

The running types spread by means of rhizomes or stolons and can become invasive. They have the ability to cover large areas and may not be the best choice for small-space gardens or in combination with less competitive perennials. Some examples include ribbongrass, blue lyme grass and prairie cordgrass. These may be useful in large open areas where a groundcover is needed or as erosion control. Another issue is that these grasses can get invasive because of their seeding potential. Northern sea oat is a grass with a handsome bamboo-like quality. However, it sets a lot of seed that can end up spreading in every direction and coming up everywhere. These grasses are useful but need to be understood. The clump formers, on the other hand, tend to grow in defined clumps or mounds and do not get invasive. These make excellent additions to the mixed perennial border. Some examples include feather reedgrass, blue fescue, autumn moor grass and Miscanthus sp.

Grasses can also be classified and selected based upon when they are in active growth. Cool-season grasses prefer the cooler months of the year and grow best at temperatures of 60° to 70°F. They start growth very early in the year and tend to go dormant when the weather starts to turn hot and dry. If drought conditions prevail, you will need to water these grasses in order for them to remain attractive landscape plants. Otherwise, they will go dormant, and in grass that means brown foliage — not the best look in the landscape. Many of these grasses also tend to be either evergreen or semi-evergreen. They flower very early in the season and may need a little grooming to keep them looking good. Examples of cool-season grass include blue fescue, blue oat grass and tufted hair grass.

The warm-season grasses prefer warm weather and do best during the hotter months of the year. These grasses tend to come up late in the season after the soil starts to warm up and air temperatures become more stable. These grasses will start to go dormant and develop fall color when the cool weather of fall arrives. Grasses that fall into this category include Miscanthus sp., Pennisetum sp., cordgrass and pampas grass.

There are a number of popular grasses that are not hardy in northern climates. Their hardiness ranges from Zone 7 southward. These grasses are still useful, especially when used as annuals and mixed in with container plants or in the annual border. Some of these grasses include New Zealand sedge, red fountain grass, fiber optic grass and Mexican feather grass. These grasses are very useful for their foliage color and texture.

SITE SELECTION AND PREPARATION

Most ornamental grasses prefer full sun and well-drained soil. There are some grasses that will tolerate partial shade conditions and do very well. If you are faced with such a site, consider things like the sedges (Carex sp.), Sweet Flag (Acorus sp.), Northern sea oats, tufted hair grass, hakone grass, wood rush (Luzula) or millet grass (Milium).

If you are faced with a moist site consider cordgrass, switchgrass, Spartina sp., Typha sp., Miscanthus cultivars, Carex sp. and Cyperus sp.

As with any perennial installation, site preparation is critical to long-term success. Incorporate organic matter to improve soil tilth. Work in 1 to 2 pounds of 10-10-10 fertilizer per 100 square feet of bed during preparation. Good drainage is critical to long-term success with grasses, especially in regard to over wintering in colder climates. If the site is poorly drained, correct the drainage if possible or consider using raised beds.

PLANTING

The availability of ornamental grasses as containerized plants allows them to be planted throughout the growing season. Late fall planting may not be as successful in northern areas because the plants do not get established well before winter. If grasses are planted in the fall, they may benefit from a winter mulch of straw around the roots. Plants should be planted no deeper than they were grown in the container and you should water them well after planting. During the establishment period, you may need to water grasses frequently to allow them to get rooted in the area. Once established, many grasses are extremely tolerant of dry periods, making them useful in landscapes that may get minimal attention.

CARE AND MAINTENANCE

Grasses are relatively easy to maintain. You may apply fertilizer at the rate of ¼ to ½ cup per plant in the case of larger specimens or 1 pound of 10-10-10 per 100 square feet of bed area. Avoid overfertilization, as it tends to encourage weak stems. Adjust fertilizer rates based on overall growth and appearance. In most instances, you will not need to apply much fertilizer to well prepared beds.

Water newly planted grasses regularly. Established grasses are fairly drought tolerant. Cool-season grasses benefit from additional watering to keep them attractive during summer dry periods.

Ornamental grasses are relatively pest free. There are, however, some things for which you need to be on the look out. During wet, cool weather, the instance of leaf spots and foliar rusts is an issue. Many times it is not bad enough to warrant spraying. Sometimes removing affected foliage and looking at providing better air circulation helps cure the problem. As far as insects are concerned, aphids, billbugs and Japanese beetles seem to be the top three pests. Control is easy with proper insecticides. Check with your local extension agent for recommended materials for your area.

Grasses do not need any special winter protection. Leave the stems standing to help insulate the crown of the plant. The stems also provide a great deal of winter interest. In the spring, just before growth resumes, cut the stems down to about 3 to 4 inches. You can then shred the stems and use them around the plants as mulch.

On occasion, you may need to divide ornamental grasses (see “How To: Divide Ornamental Grasses,” Grounds Maintenance, March 2004). The standard suggestion of every 3 to 4 years is just that, a suggestion. Whether a plant needs division will depend on the overall appearance and performance. If the center of the plant starts to die out with only a green ring of growth being produced and flower and foliage quality is on the decline, it's time to divide. Late winter and early spring are the best times to divide most grasses. Large clumps can be a challenge to lift and divide. Make sure you are armed with a strong-handled spade and a strong back. After the clump is divided, cut it up into sections, discarding the dead center. These segments can then be replanted and watered in as well.

Greg Stack is an extension horticulturist for the University of Illinois Extension (Matteson, Ill.).

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