Ornamental grasses are very effective plants in the landscape. Grasses, in general, are full sun plants that are well adapted to low maintenance landscapes. Grasses are drought tolerant, provide mass impact and provide multiple seasonal interest. Grasses are also deer resistant landscape plants. Ornamental grasses need to be cut back in early spring, preferably March, as close to the ground as possible. This is also a good time to divide any clumps that have outgrown their space. Blooming can occur on some varieties as early as June.
In order to find an ornamental grass that bests fits your needs, there are a number of factors to consider, including climate, soil type, and personal preference..
Cool Season Grasses
Cool season ornamental grasses include fescue, blue oat, tufted hair, and autumn moor grass. They usually begin to grow in early spring, and many remain semi-evergreen over the winter. Some require a mid-summer cut-back to ensure fresh foliage for fall. Cool season grasses thrive when given ample amounts of water. Division can usually be done in either spring or fall to keep them healthy. They will grow in many types of soil, making them ideal for places in your yard where other plants won’t grow.
Warm Season Grasses
Some popular warm season ornamental grasses include Japanese silver, Pampas, Northern sea oats, Perennial fountain, and Prairie cord grass. These grasses thrive during warmer times of the year and can withstand high temperatures and humidity. Warm season grasses, unlike cool season grasses, do not show growth until soil is warm. They usually become brown in the fall, and require only a cutback to near ground level in early spring before new growth commences. They do not require as frequent division as cool season grasses (divide only in spring).
Understanding growth patterns
There are two main ways that ornamental grasses grow.
1. Clump forming grasses, literally, grow in mounds or clumps. They usually mix well with other perennials, and are not invasive but, increase in diameter over time.
2. Rhizome forming grass, also called running grasses, spread by underground stems.
They can become both invasive and aggressive.
Caring for Ornamental Grasses
Once you have decided on an ornamental species and planted it, which is usually done in the spring or the fall, your grass will need proper care.
After the first season of planting, make sure that ornamental grasses are well watered. Established plants do not need regular watering, except in times of drought. Please note that water requirements vary depending on grass species, location, size, and the growth rate desired.
Ornamental grasses require low levels of fertilizer. A slow release fertilizer is ideal, and will ensure healthy grass throughout summer. Please note that nitrogen levels should be kept low so that “flopping” is avoided.
An application of mulch, which limits weed growth, should be placed around grasses. Since mulch also retains water well, it will also help to lower watering frequency.
Cutting and Maintenance
Ornamental grasses fall into two main groups, evergreen and deciduous.
1. Deciduous grasses need cutting back annually so that they will look their best.
2. Evergreens just require a tidy-up.
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.
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. 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.
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 sheared 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. 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. 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.
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 transplanting 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.