Ornamental Grasses

Ornamental grasses are ideal garden plants. Most are quite vigorous, require minimal care and add aesthetic virtue in terms of color, form and texture to the landscape. They are available in sizes ranging from as short as six inches to tall as fifteen feet that can tolerate a wide array of exposures and soil types. Most are reliably winter hardy at our latitude which makes annual re-planting unnecessary. Add to this their ability (in many cases) to tolerate hot, dry weather and it is no wonder that ornamental grasses are enjoying a great deal of popularity in the gardening world today.

Common quaking grass. Easily grown in average, medium wet, welldrained soil in full sun. Tolerant of a wide range of soils. Cut back clumps immediately after seed heads disintegrate to encourage additional foliage growth. Clumps may be mowed on high setting in late fall or dead foliage can be cleared in late winter. Photo courtesy of Missouri Botanical Garden Plantfinder.

Ornamental grasses usually are classified first according to their temperature preference: cool-season or warmseason. Cool-season grasses (many of which are evergreen) prefer temperatures in the 60 to 75 degree F range. They make significant growth early in the spring (April and May) and again later in the fall (September and October). They are not well-suited to hot, dry conditions and frequently go dormant during the heat of summer. On the other hand, warm-season grasses thrive at temperatures in the 80 to 95 degree F range. They are a bit late to emerge in the spring (late April and May) and make their major growth when temperatures are warm. Warm-season grasses tolerate hot weather very well and remain attractive well into the fall, when many of them have added interest because of their attractive flowers. Warm-season grasses die back to the ground after the first hard freeze of the fall but retain ornamental value in a dried state well into the winter.

Another method of classifying ornamental grasses is according to their growth habit. Most ornamental grasses are clump forming rendering them non-invasive and suitable for use as specimen plants or for massing. These grasses exhibit a wide array of architectural forms including tufted, mounded, upright, upright divergent, arching and upright arching. The shortest ornamental grasses usually exhibit a tufted habit of growth while the tallest are upright arching in form. A second classification of ornamental grass according to their growth habit is spreading or running. These grasses creep or spread thanks to aboveground structures called stolons or below-ground structures called rhizomes. They can be quite invasive and choke out neighboring vegetation. While this is undesirable as a companion plant in the ornamental garden it is a preferred trait for a plant to be used as a single species to be used as a ground cover or to stabilize soil. Spreading ornamental grasses can be contained in mixed plantings by cutting the bottom out of a five or seven gallon nursery container, sinking the container into the ground until its top is level with the surface of the soil and planting the grass in the center of the container.

As a rule, ornamental grasses are tolerant of soil conditions although most prefer a well-drained garden loam fairly high in organic matter. Most ornamental grasses are full-sun plants and should receive at least six to eight hours of direct sun each day for best growth. Application of between one and two pounds per 100 square feet of a complete, general purpose garden fertilizer such as 5-10-5 or 10-10-10 before planting should supply adequate nutrients for quick establishment. Once established, ornamental grasses should not be heavily feed; application of one-half to one pound of either of the afore- mentioned fertilizers per 100 square feet is sufficient. This is equivalent to about one-fourth to one-half cup per plant. Apply fertilizer in the spring just as new growth emerges. Excessive fertility (especially in the form of nitrogen) encourages lush, weak growth unable to stand on its own. Additionally, late applications of fertilizer to warm season grasses tend to reduce their winter hardiness.

Cool-season ornamental grasses can be planted during the spring or fall; warm-season grasses should be planted only in the spring. Fall-planted grasses benefit from a light mulch applied after several hard freezes have occurred their first winter. Winter protection during succeeding years usually in not warranted. Spacing ornamental grasses is a matter of personal preference and intended function in the garden but, for small groupings, spacing them a distance apart equal to their mature height is considered satisfactory. Grasses should be watered regularly during their first season of growth to encourage the establishment of a deep, vigorous root system. Once established, ornamental grasses usually require supplemental irrigation only during periods of hot, dry weather. This especially is true for warm-season grasses. The amount of water to apply depends on several factors including species, exposure, soil type and size. Additionally, most ornamental grasses are remarkably pest-free and usually do not warrant the application of pesticides.

Reed grass. This species of reed grass is a slowly-spreading, clumpforming, warm season ornamental grass which features a mound of narrow, stiff, green leaves (1/4 to 5/8" wide) typically growing to 2’ tall and as wide. Photo courtesy of Missouri Botanical Garden Plantfinder.

Routine maintenance procedures include cutting back ornamental grasses in late winter or early spring to remove old, unsightly growth and to allow new growth to develop without being shaded by the old. Clump-forming grasses should be divided regularly to keep the clump "young" and attractive. Older clumps tend to die in the center leading to an unattractive shape and appearance. Frequency of division depends on species, soil fertility and exposure but dividing every third year is a safe "rule-of-thumb" for most species. This should be done in late fall or early spring when the plant is dormant.

Ornamental grasses have many uses in the landscape. Their wispy, graceful foliage add interesting form and texture to both beds and borders. Taller species make effective screens while medium-sized species combine well with foundation plantings around the home. Shorter species can be incorporated into plantings of annuals or perennials, or planted in masses for an interesting carpet bed effect. Spreading or running species are quite effective in stabilizing soil on steep banks or attractively occupying an area that is difficult to maintain. All ornamental grasses flower (most producing panicles, racemes or spikes), giving them additional appeal. While the flowers of most are not especially colorful, they do add interest and appeal and often are produced in late summer or early fall--a time when the garden could use a bit of change.

Next month: A description of popular ornamental grass species for the Midwest.

David Trinklein
Associate Professor of Plant Sciences