Maintaining Ornamental Grasses

If they're properly selected and placed, most ornamental grasses need very little care or maintenance. However, some grasses do best with an extra attention at various times of the year.

Watering

Once the plants are rooted, adjust watering to individual needs. In hot, dry climates, newly planted grasses may need water several times a day to be kept sufficiently moist. Keep the foliage cut back to one-fourth or one-third to reduce transpiration. Renewed, vigorous foliage will soon return. If newly planted grasses do get scorched or suffer dried foliage, simply cut back to force new growth.

The growth of grasses can be regulated by watering or withholding water, especially in dry southern and western climates. Water the grass regularly and it will grow lushly and copiously; ration the water and the plant may be tight and slow-growing. In dry climates, water can literally be used as a growth regulator. On a dry slope, for example, the foliage of dwarf pampas grass (Cortaderia selloana 'Pumila') may reach 3 to 4 feet tall and 4 feet wide with flowers 2 to 3 feet above the leaves. But, on an irrigated golf course in rich soil, its foliage can reach 6 feet tall and 7 feet wide with flowers 3 to 4 feet above the foliage-hardly a dwarf.

Avoid extreme watering regimes. Grasses used to growing with lots of water will scorch easily if water is withheld. If this should occur, renew foliage by cutting back to the crown and resuming regular watering. Cool-season grasses can be cut back one-third, but most warm-season grasses need a hard chop. Warm-season grasses that have suffered drought stress may need to be cut to within several inches of the ground so that all-new foliage reemerges. It is surprising how fast new growth returns-many grasses can grow 1/2 inch per day.

Watering grasses can pose an interesting challenge to the homeowner. Water is most efficiently supplied if it can get directly to the roots; thus, overhead spray irrigation is not as efficient as drip irrigation. In some cases, watering from above also causes a more rapid decline of the flowers. The rapid growth in height of some grasses may defy overhead irrigation as well. How spray over a 6-foot grass? The best way to water is at the base of the plant. Drip hoses or bubblers are efficient ways to irrigate. One note of caution: If you install sprinkler heads, remember where you have placed them, or you may inadvertently cut them when you are cutting back the foliage.

Cutting back the foliage

The single most important maintenance rule for growing healthy, attractive grasses, with few exceptions, is to cut back the foliage at least once a year. New plantings of cool-season grasses may not need clipping until the end of their second season. In mild climates, some cool-season grasses may not require yearly cutting back, unless the foliage is unattractive or thick with old leaves. Some people do not cut back their grasses at all. The combination of old growth and new growth may look messy, but it doesn't affect the health of the plant.

Cutting back is a substitute for the natural processes of periodic burning and grazing that take place in natural grassland ecology. Spring burning removes last year's growth and exposes the soil to the warming rays of the sun, a boost for newly emerging grasses. While many grasses prefer to be burned, it is dangerous and often not possible for the home gardener. In many prairie plantings, burning is a recognized method of range management.

Cut back ornamental grasses just before or as the new season's growth begins to appear. It's best to cut most grasses back in late winter-generally, late February or early March, depending on climate. This timing allows you to enjoy the glories of winter foliage.

As winter deepens, warm-season grasses take on their winter look. Many grasses have pale parchment or ruddy winter foliage that appears warm and bright under overcast skies. They hold this color well into the season, and are lovely when contrasted with a white blanket of snow under dark skies. Cutting in the fall would eliminate these grand winter effects.

Dormant grass left standing keeps the garden alive in winter with sound and movement. Graceful leaves and seed heads bend and rustle in the wind, adding interest even if admired through a window. Birds and wildlife visit the winter garden, seeking seeds and shelter. On the practical side, dormant foliage above the plant helps insulate it from cold and rain, and old foliage directs water away from the clump and helps prevent rot. Cutting back early will remove this protection. Still, some gardeners prefer a tidy look and cut back their grasses in the late fall, after fall color has left the foliage.

In mild climates, fall cutting can provide early renewal. The new season's growth begins to emerge in early winter, sometimes even in late fall. In these cases, cutting back early means a more attractive plant earlier in the season. In dry southwestern climates, dormant foliage may pose a fire hazard, and the removal of dormant foliage may be the law.

Most grasses should be cut back to within a few inches of the ground. Some grasses, usually cool-season grasses, do not like to be sheared too closely. Many feather grasses (Stipa spp.), for example, resent a close cut. Often, plants shorn too closely will not recover. To be safe, unless you have been successful in the past, cut back cool-season grasses to two-thirds of their full size. Cutting old foliage before the new foliage arises is easier than trying to work around newly emerging shoots. Avoid damaging new shoots, but don't despair. A new crop will usually replace any that you accidentally slice off.

In a small garden, a sharp pair of hand pruners will work well for most cutting. Grasses with soft foliage can be cut with a string trimmer, though this often leaves a ragged appearance. Tough, tall perennial grasses are most easily cut by a weed trimmer with a saw-blade attachment. Keep all blades sharp. Some grasses develop thick canes with lots of silica in the foliage, which can quickly dull a blade. Some grasses, usually spring bloomers, have spent flowers by midsummer that can look tattered and unattractive. Remove them once they have finished blooming. Cut the stems below the top of the foliage so the old stalks aren't visible.

A few grasses, especially wild ryes (Elymus spp.), can be sheared several times in the same season to force new growth. Shearing this grass in midsummer forces fresh, new metallic blue foliage for the late season.

In mild climates, some warm-season grasses like kangaroo grass (Themeda spp.) are sheared in September to force new growth for the fall. Although the flowers are sacrificed, the fall foliage is particularly showy. More experimentation is being done with this method to help sharpen and improve fall color on warm-season grasses in mild climates. While not as many flowers form on the new growth, still some will often appear: The trade-off is richer fall color later in the season.

Staking

Floppy grass foliage and flower stems are usually caused by insufficient light, over-fertilization, or excessive amounts of nitrogen. If you have a large, floppy grass, secure strong metal pipes in or near the clump, sinking them close to ground level. As the grass grows, insert smaller-diameter -pipe into the tubes, and discreetly cover the supports with foliage. Remove pipes before cutting back the grasses. Support smaller grasses with wire loops, twiggy brush, or other holders as you would perennials or vegetables.

Dividing and transplanting

Grasses are divided and transplanted to propagate more plants, to renew older existing plants, and to relocate existing grasses. Many grasses require thinning or dividing to keep them looking their best. Older clumps may flop or grow too large for the space they occupy, or they may die out in the center and require rejuvenation. Growing trees and shrubs may provide too much shade for older grasses, requiring their removal and replacement with more shade-tolerant grasses. Large grasses that have been improperly placed may need to be moved to a more suitable location. Divisions and transplantings are done at different times of year; depending on the type of plant and the plant's condition.

Warm-season grasses are best divided in late winter and early spring, and cool-season grasses in fall, winter, and early spring. A good method of gauging when to divide a grass is to watch for signs of active growth. Grasses may tolerate division at other times of the year, but the best time to divide is usually as new growth begins. Subtropical and tropical grasses can be divided even when actively growing.

Digging and dividing large clumps requires a strong back, a sharp axe, a saw, a shovel, and lots of work. Though many grasses tolerate being completely bareroot, it's always best to keep some soil on the roots of the plant you are digging. First divide the plant into fairly good-sized divisions. Most grasses can be divided further, into small shoots, if you want lots of divisions, but it will take them longer to reach full size than larger divisions.

When dividing grasses, cut the foliage back one-fourth to one-third to reduce loss of moisture through transpiration. Always keep newly divided plants moist and in the shade until they are in the ground.