What makes ornamental grass "ornamental?" I like to think there are two reasons, both of which are good arguments for including it in your landscaping.
Firstly, this is not the "grass" that many of us have reluctantly been mowing since our childhoods, to contrast which with ornamental grass we might term, "functional grass." Such functional grass serves primarily a practical purpose: namely, it forms a uniform surface on which to walk when we're out in the yard.
Outdoor carpeting, if you will. Ornamental grass, by contrast, is not meant to be mowed, is not meant to be uniform, is not meant to be tread upon.
Secondly, in terms of aesthetics, functional grass is mainly negative space. That is, its job is not so much to be admired itself as it is to form a stage on which the yard's actors (flowers, shrubs, trees, hardscape, etc.) play their roles. Ornamental grass, by contrast, is one of the yard's actors. The only purpose of ornamental grass is to be pretty, to be an "ornament."
Ornamental grass is used in landscape design the way one uses flowers, shrubs and trees. In fact, it is often mixed with such plants to fill planting beds, creating diversity in terms of form and texture. When composing such planting beds, it is best to layer the plants, placing the tallest in the back, the shortest in the front and the rest in the middle. For this reason, I categorize the ornamental grasses below in terms of their height.
Tall Ornamental Grasses
No fall or winter landscape should be without a tall ornamental grass. Plume grass (Erianthus ravennae) is grown in zones 4-9. It grows 8'-11' (its clump has a spread of 3'-4'). This plant, with its tall, thin shafts and fluffy coiffures, exhibits a delicate structure that lends a touch of charm to the harsh winter landscape.
Because of its height, a plant such as plume grass can be used as a focal point.
Maiden grass (Miscanthus sinensis 'Gracillimus') is a fine choice in zones 5-9 for a tall drought-tolerant ornamental grass, as it reaches as much as 7’ in height, with a spread a bit less than that. Maiden grass (middle photo) bears coppery tassels as a seed-head in early fall, eventually growing lighter in color and adorning the plant as a "plume." Don't cut the clump's stems back until after the bleakness of winter passes, since the graceful stems and puffy plumes of this plant will provide some visual interest on an otherwise barren December-February landscape (see below: How to Trim Ornamental Grass).
"But," you might object, "it's mainly late in the season that Miscanthus sinensis 'Gracillimus' provides much of a display (after it blooms); I wish it offered more to look at earlier in the year." Enter Miscanthus sinensis 'Zebrinus'. The "zebra" markings on its leaves provide plenty of visual interest even before it flowers.
Intermediate Ornamental Grasses
Purple fountain (Pennisetum setaceum 'Rubrum') is a tropical ornamental grass. If you live in an area subject to harsh winters, you'll need to treat it as an annual. The plant reaches a height of 3-5 feet with a spread of 2-4 feet. Its purplish flower spikes (image) are succeeded by fluffy, attractive seed heads tinged with purple or burgundy. Its spiky foliage is also burgundy in color.
Blue oat grass is a mounding, cool-season ornamental grass suitable for USDA planting zones 4-8. Known botanically as Helictotrichon sempervirens, deer tend to leave this plant alone. This ornamental grass attains a height of 2-3 feet tall, with a similar spread. Grow it in full sun and well-drained soils, if you wish to enjoy the signature blue hues of its foliage to the fullest. The plant also produces spiky, dark flowers with a bluish tint in summer that turn harvest gold in autumn.
Northern sea oats (Chasmanthium latifolium) is an ornamental grass that grows 24"-36" high in loose clumps of green foliage. Its name derives from its seed pods, which look like oats. This deer-resistant ornamental grass is cold hardy to zone 5. Even after its leaves have dried and died, it provides visual interest to the winter landscape.
Short Ornamental Grasses
For a shorter deer-resistant plant, try liriope, or "lilyturf" (Liriope spicata). Lilyturf (not a true ornamental grass, by the way) can be grown in zones 4-10 and reaches only about 1' in height. Lilyturf likes water, but also prefers well-drained soil. Select an area with partial shade and soil rich in organic matter for best results. This ornamental grass, too, has a spiky flower, ranging in color from white to lavender. In autumn it bears a dark berry. You'll want to contain this plant, however, because it is invasive. See bottom picture to find out what liriope looks like.
Likewise, black mondo grass does not belong to the Poaceae family, but it functions in landscaping as if it did. Also like liriope, it can be invasive. Black mondo reaches 6 inches in height. Its striking color combines well with plants that bear golden or chartreuse leaves. Carex 'Spark Plug' is another imposter (it's a type of sedge) that nonetheless plays the "shorty" role well, reaching only about a foot in height.
Another short ornamental grass (around 1’ x 1’) grown in zones 4-8 is blue fescue (Festuca glauca 'Elijah Blue'). The popularity of this clumping, drought-tolerant ornamental grass lies in the blue color of its foliage, which will beautifully complement any surrounding plants you may have with silvery foliage, such as lamb's ears. The plant rather resembles a pincushion bristling with blue pins. As with maidengrass, cut back foliage in early spring. Divide every few years to rejuvenate.
If you prefer your blades to be gold-colored, try golden Hakone grass. It can be tricky to achieve optimal coloration with this plant, but my own has turned a wonderfully warm golden color when grown in shade. It also offers wispy seed heads in fall that I find attractive.
How to Trim Ornamental Grass
"How do you trim ornamental grass?" is a question I get frequently. Most people understand that ornamental grasses need a good "haircut," at some point, after they have turned brown. It's just a question of when.
While some tidy folks may prefer to trim ornamental grass at the end of autumn, to give the landscape that "clean-cut" look before winter sets in, I think more of us prefer to do it in spring. Heck, winter interest is one of the main excuses for growing ornamental grass. Just make sure that, when spring does come, you cut back the plant early enough to get the old growth out of the way before the new growth emerges. Otherwise, you will be worried about mistakenly trimming the new shoots, since they will be right in your way as you attempt to remove dead stalks.
So much for what might be considered the "when" part of the question. But the "how" may be worth considering, too -- if you want to avoid making a mess when you trim ornamental grass. Otherwise, your garden will end up looking like a barber shop floor, after a customer has just left. To avoid this mess, tie the dead stalks up into a bundle before you make your cuts. That way, after the cutting is done, you mainly have just one object to pick up and move, rather than all of the individual stalks.
Low-Maintenance Landscaping With Ornamental Grass and Mulch
Whether you mix ornamental grass with shrubs, trees and flowers or let it stand alone, you'll want to apply mulch around ornamental grass. Replacing lawn grass with a combination of mulch and ornamental grass can reduce yard maintenance requirements. While this may not be feasible for large areas, it is certainly an option for small plots of land. Remember, maintaining lawn grass goes beyond mowing time. It also includes such tasks as mower maintenance.