Ornamental Grasses in the Garden

Ornamental Grasses in the Garden

By Published February 06, 2023

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Color, dramatic shapes, ethereal textures, movement, sound, winter-interest, wildlife habitat and wildlife food; all of these and more are what ornamental grasses add to a garden.

The visual aspects of a garden design are color, shape, and texture. The foliage of modern ornamental grasses is no longer just green, but comes in a range of colors including yellow, blue-grey, red, purple, and near black or striped with white or yellow or banded with yellow. These new colorful grasses are exciting, yet it will always be the shapes and textures of grasses that make them indispensable for pleasing and dramatic garden displays. The dramatic contrast between the shapes and textures of grasses and other ornamental plants highlights both groups of plants: the ornamental grasses and the forbs.

Few plants add the element of movement to a garden to the degree that ornamental grasses do; their billowy flower heads move with the slightest breeze. Their rustling suggesting whispered secrets, not quite heard clearly enough to decipher.

Ornamental grasses belong in our gardens as we strive to create gardens that not only delight our senses but also support other creatures. The dense growth of many grasses provides shelter for small creatures during the trying spells of winter weather. And many grasses provide nourishing seeds for birds. Great advances in the selections of ornamental grasses are now a common occurrence. A few of the breakthroughs include a wider range of foliage color, compact and/or sturdier stems to ensure that those species prone to flop, don’t flop, and sterility in exotic species (non-native species) so invasiveness is no longer an issue.

Switch Grass – A North American Native

Panicum virgatum is commonly known as switch grass. It is a widespread North American native and it is an essential choice wherever ornamental grasses are grown. It starts off quietly in spring into early summer providing the slender grassy texture that contrasts nicely with other herbaceous perennials and woody plants. It starts to come into it own as it begins to bloom in mid to late summer. The billowy flower heads (panicles) rising like clouds above their neighbors. Though fall’s killing frosts steal the color from switch grass, rendering it sepia tan, its structure remains flawless all winter. Indeed, it is one of the most beautiful of the winter-dormant herbaceous perennials in its winter-brown form. Add to this the fact that it is extremely easy to grow, wanting sun and most any soil ranging from wet to fairly dry. Switch grass is also very low maintenance, usually only needing to be cut to the ground in late winter before the new growth starts.

Panicum virgatum, switch grass, was never a plain Jane. Even so, the many new selections now have the “wow” factor.  Few grasses have red foliage (and we do mean red and not burgundy) but there are selections of switch grass that do. The Panicum virgatum cultivar ‘Shenandoah’ was one of the first selections with red foliage. There are newer red leafed cultivars such as ‘Hot Rod’ and ‘RR1’ (sold as Ruby Ribbons) which color up earlier in the summer. These red foliage cultivars are also quite compact, about 3’ tall on average, so are good choices for smaller spaces.

There are many cultivars of switch grass with blue-gray foliage. ‘Dallas Blues’ is an industry standard. It is a robust 6’ tall selection with large, very handsome panicles (flower heads) The panicles have a very architectural structure of multiple layers making up a conical inflorescence as opposed to the diaphanous cloud of most other Panicum. ‘Heavy Metal’ is also blue foliaged but of a very different growth habit being strictly upright and narrow in outline. It generally tops out at less than 4’ tall.

To an increasing degree, new cultivars of ornamental grasses are the result of intentional breeding programs and not just good selections from wild populations. Three very recent introductions of Panicum virgatum, all with blue-grey foliage, are ‘Gunsmoke’, ‘Blue Fountain’ and ‘Niagara Falls’. ‘Niagara Falls’ is the smallest of the three, maturing at 4’ tall and wide, with a waterfall of long arching blue tinted foliage. ‘Gunsmoke’ is a bit taller at 4.5’ tall and more upright. Its foliage color is a greyer blue which contrasts with its purplish plumes. ‘Blue Fountain’ is the giant of the three, growing to 7’ tall, though quite a bit narrower and strictly upright.

Many other cultivars of Panicum virgatum are available, especially if one takes the time to search out nurseries specializing in ornamental grasses. The home gardener and the professional garden designer alike can find cultivars of the correct size, desired foliage color and growth habit for their particular needs. Switch grass offers other features beyond these visual aspects including many that support a habitat garden. The caterpillars of several moths and butterflies use switch grass as larval food. The seeds are utilized by a wide range of birds. On warm winter days one can hear the “pop” of seeds being expelled explosively.

Andropogon – One of America’s Prairie Grasses

Several native species of Andropogon are excellent garden ornamentals. The most frequently encountered species of Andropogon, A. virginicus, is the ubiquitous broom straw of abandoned farm fields and sunny roadsides. All winter long it paints such locations with its red-brown foliage. It is rarely invited into gardens except for large ones where prairie type plantings are being attempted. More commonly cultivated is Andropogon gerardii, the big bluestem or turkey foot. It is one of the tall grasses of the tall grass prairie ecosystem. Though tall it is strictly clump forming, with a rather tall, yet thin and see-through habit. Many cultivars have been selected for good fall foliage color. Some modern cultivars have colorful summer foliage, including blue foliage, the best known of these probably being Andropogon gerardii ‘Lord Snowden’s Big Blue’. More recently, cultivars such as ‘Black Hawks’ add near black foliage to the mix.

Two species of Andropogon that are rarely encountered in gardens despite their gorgeous winter presence are Andropogon glomeratus and Andropogon ternarius. A. glomeratus has the common name of bushy beard grass. It is much like broom straw in appearance but with great clusters of bracts making for a much more substantial display, all of which turns a rich russet brown and stands attractively all winter. A. ternarius, the split-beard broom sedge, is a slender thing about the stature of broom straw and easily mistaken for it until it blooms at which point the inflorescences become silvery fluff. They sparkle when backlit by the low winter sun. This species is extremely drought tolerant while the previous species, Andropogon glomeratus, occurs in wet sites, though it will tolerate average moisture soil in gardens.

Little blue stem, Schizachyrium scoparium, is closely related to Andropogon and is much like the smaller members of that genus. Little blue stem is a clump former growing usually to 2 to 3’ tall. Many new cultivars have been introduced with colorful, often multi-colored, foliage. Blue foliage cultivars are common and numerous. ‘Standing Ovation’ is a dramatically upright 3-footer with green and blue foliage with some red highlights. ‘Twilight’ almost must be seen to be believed. It starts off blue-green and over the course of summer transitions to a glowing lavender-plum color. ‘Chameleon’ is a variegated cultivar with white margined leaves which develop a pink overlay late in the growing season. All little blue stems end up russet-brown after a frost but remain ornamental nearly all winter long. They require a sunny location and do best in drier, lower fertility soils than most plants.

Indian Grass – A Great Selection for Southern Gardens

Another native grass of great ornamental value is Sorghastrum nutans commonly called Indian grass. It is a fairly small clump of unassuming foliage waiting in the wings through the summer months which then transforms to its starring role as a 5 to 7’ tall vertical bouquet of rich bronze-colored panicles in early fall. ‘Indian Steel’ is an especially beautiful cultivar with blue-grey foliage and large inflorescences. The cultivar ‘Slim Pickens’ is a remarkable, upright, blue foliaged form that was selected from the South Carolina Botanical Garden in Pickens County, South Carolina, so it is a good selection for gardens in warmer more humid parts of the country. Sun and average soil moisture are all it needs. Maintenance is easy, merely cut it down in late winter before new growth starts. Its less bulky size means there’s less to cut back.

Fountain Grasses – Showy, Long-lasting Grasses for the Garden

The Fountain Grasses are members of the large genus Pennisetum. Two species Pennisetum alopecuroides and Pennisetum orientale are widely grown and for good reason. They supply many months of showy bottle brush inflorescences.

Under some growing conditions, in some parts of the country, Pennisetum alopecuroides can produce unwanted seedlings. Plant breeders at the University of Georgia have introduced sterile cultivars in a range of sizes for guilt free planting. These cultivars bloom their heads off and their cultivar names will have you hankering for some good Cajun cooking. ‘Praline’ matures at 2’. ‘Hush Puppy’ and ‘Jambalaya’ grow to 3’ tall and wide. ‘Jambalaya’s flowers being a bit spicier in color (pink aging to silver) compared to the normal cream colored. ‘Cayenne’ is a bit bigger at 4’ and has dark brown plumes. ‘Etouffee’ is the largest of all, topping out at 5’ tall by 6’ wide. Its plumes are tan aging to bronzy lavender. Pennisetum alopecuroides is showy from summer well into winter. Even after the bottlebrush shaped inflorescences shatter by mid-winter, the foliage remains attractive until late winter when it must be cut down before new growth starts. Though thriving in full sun and tolerant of a wide range of soil conditions this species performs quite well in bright shade and part sun/part shade situations.

Another exciting breakthrough are several yellow foliaged cultivars of Pennisetum alopecuroides:  the 2’ tall ‘J S Jommenik’ and the 3.5’ ‘Lemon Squeeze’. To now have the slender leaves of fountain grass in bright yellow invites all sorts of fun contrasts with broad leafed neighbors. These yellow foliaged selections must be grown in sun to keep their bright yellow color, though even in a sunny location they will become greener as summer progresses.

Pennisetum orientale is quite a bit different from the previous species in that it flowers most of the frost-free part of the year and is of no winter interest to the gardener’s eye. Though thoroughly worth growing for its summer-long bloom, it is best cut to the ground after frost to eliminate its raggedy mound of foliage. It is also a slenderer species with gracefully arching flower heads which dance with the slightest breeze adding the element of movement to the garden.

Years ago, the only cultivar available was a short one, not much more than a foot tall. It was common then and circulated without a cultivar name. Hopefully it will become available again for it is valuable for small spaces and amongst smaller neighbors. ‘Karley Rose’ has deservedly become an industry standard with its rosy plumes and 3’ height. ‘Shogun’ differs from ‘Karley Rose’ only in that its plumes are white instead of pink. It too has become hard to find. ‘Tall Tails’ is a very different beast at nearly 6’ tall in bloom and denser inflorescences but superb where there is room for it. It will tolerate wet. All of these selections of Pennisetum orientale can be cut to the ground in midsummer if they become shabby after months of bloom, which they often do in areas with long growing seasons. They will quickly regrow and resume blooming and continue fresh up to frost.

Ornamental Grasses Should be Included in All Gardens

This is a very exciting time to be adding ornamental grasses to our plantings with all of the new introductions and breeding work improving what is available. Grasses should be included in all gardens. Their beautiful, striking forms add an element that is different from the other flowers in the garden or the more static forms of conifers and other woody plants. This is just a tiny taste of the true grasses that can add so much beauty to ornamental gardens and support wildlife in habitat gardens. All gardens should strive to be not only places of beauty and peaceful retreat from a bustling world, but also support the other creatures who share this planet with us. There are so many other grasses to consider, not to mention members of the sedge family, the Cyperaceae and other grass-like plants.
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