What ornamental grasses are and what they look like
Ornamental grasses are grown for their foliage, form and movement rather than for showy flowers. Most make a clump of narrow, arching or upright leaves, and in summer or fall they send up feathery plumes, bottlebrush spikes or airy seed heads. Many turn gold, bronze or straw-colored in fall and keep their shape into winter.
The group is usually stretched to include grass-like plants such as sedges (Carex) and rushes, which are not true grasses but are used the same way in the garden. Sizes range from small blue fescue mounds under a foot tall to Miscanthus and plume grass that can top head height. For an overview of the main kinds, see types of ornamental grasses.
Names vary a lot between regions, so it helps to know the botanical name of what you are buying. Our guide to common names for grass plants sorts out the most frequent ones.
Know your type: cool-season, warm-season, evergreen
Almost every care question depends on which of three groups your grass belongs to (compared in detail in warm-season vs cool-season ornamental grasses).
- Cool-season grasses (for example fescues, feather reed grass, blue oat grass) start growing early in spring and grow most in spring and fall. They may slow down or look tired in the heat of midsummer.
- Warm-season grasses (for example Miscanthus, switchgrass, fountain grass, muhly grass) wake up late in spring and put on most of their growth and flowering in the heat of summer. They turn brown after frost.
- Evergreen grasses and grass-like plants (many sedges, some fescues, mondo grass) keep foliage through the year in milder climates and need a lighter touch when you tidy them.
If you are unsure, the plant tag or the nursery listing normally says which group a plant belongs to.
Clumping vs spreading
Most ornamental grasses form a clump that slowly widens over the years and stays where you put it. Some spread by underground rhizomes or above-ground stolons, and a few can become a problem in beds with neighbors you want to keep. Ribbon grass and silver banner grass are examples that extension sources describe as vigorous spreaders. Some grasses also self-seed freely in certain regions, so check with your local extension office or native plant society before planting anything that may escape into wild areas.
If you want a spreader, a bottomless nursery pot sunk into the soil is one commonly suggested way to slow it down, though it is not foolproof.
Sun, soil and site
Most ornamental grasses do best in full sun, meaning at least six hours of direct light a day, and in soil that drains well. A handful, such as Japanese forest grass and many sedges, are happy in part or full shade. Heavy, constantly wet soil is a common cause of failure for grasses that prefer drier ground. Feather reed grass and some switchgrasses are more tolerant of heavier soil than most.
Planting and spacing
Spring and early fall are the usual planting windows. Warm-season grasses are generally best planted in spring so they have the whole summer to root; cool-season grasses can go in either spring or fall. Our step-by-step guide to planting ornamental grasses covers depth, watering and mulch, and the guide to spacing ornamental grasses helps you work out how far apart to set them.
Watering
Newly planted grasses need regular watering through their first season while roots establish. After that, many are drought tolerant and need extra water only in prolonged dry spells, though this varies by species. Native prairie types are generally more drought tolerant than some fountain grasses, which dislike drying out completely. Brown leaf tips are a common sign that the soil has been too dry.
Feeding
Ornamental grasses usually need very little fertilizer. Too much nitrogen tends to produce lush, weak growth that flops. Where soil is poor or plants look pale, a light feeding in spring as growth starts is the usual advice. See whether and when to fertilize ornamental grasses for more detail, and why grasses flop over if yours already do.
Cutting back
Yes, most clump-forming grasses benefit from an annual cutback. The simplest approach is to leave them standing over winter and cut deciduous grasses back in late winter or early spring, before new shoots appear. Evergreen types are usually just combed or tidied. The details for each group, plus the fall-trimming exceptions, are in our guide to cutting back ornamental grasses in spring or fall. If you want to know what to do with the plants in autumn specifically, see what to do with ornamental grass in the fall. Mondo grass has its own timing, covered in when to cut back mondo grass.
Dividing
Clump-forming grasses can die out in the middle as they age. Dividing every few years renews them and gives you free plants. It is best done when the plant is actively growing but not flowering. The full method is in our guide to dividing and transplanting ornamental grasses.
Winter care
Established grasses in the ground usually need little winter protection. Leaving the foliage standing protects the crown and gives the garden structure. Newly planted grasses may benefit from a light mulch, and tender species such as purple fountain grass are often treated as annuals in cold climates. Grasses in containers are more exposed than those in the ground. See overwintering ornamental grasses in the ground and in pots.
Growing in pots
Many ornamental grasses grow well in containers, which also helps contain spreaders. They dry out faster and run out of nutrients sooner than grasses in the ground. We cover the details in do ornamental grasses do well in pots.
Common problems
Most ornamental grasses are largely free of pest and disease problems. The two complaints that come up most often are floppy clumps and missing plumes. Both are usually linked to too much shade or too much feeding, among other causes. See why ornamental grasses flop over and why your ornamental grass isn’t blooming.
Frequently asked questions
Do perennial grasses come back every year?
Most ornamental grasses sold for the garden are perennials and return each year if they are hardy in your zone. Some, such as purple fountain grass, are tender and are treated as annuals where winters are cold. Check the hardiness range for your plant.
Does ornamental grass need to be trimmed?
Generally yes, once a year. Cutting back removes old growth so fresh shoots are not shaded or hidden. Evergreen types need only a light tidy.
Does ornamental grass spread?
Clumping grasses widen slowly and stay in place. Running types spread by rhizomes or stolons, and some grasses spread by seed in certain regions. Choose carefully if you want a well-behaved border; non-invasive clumping grasses are the safest bet.
How long do ornamental grasses live?
It depends on the species and the care they get. Some sources say anywhere from a few years to a decade or more. Dividing aging clumps helps them stay vigorous.