September leans gently into fall as if it’s exhausted from the heat and hustle of summer. Autumn officially begins on the 23rd, but the season begins for many with Labor Day, with back-to-school and with the appearance of ornamental grasses aging in the garden. Nothing evokes harvest time like grasses and grains waving lazily on the breeze.
Chasmanthium latifolium is the epitome of the fall grass. It’s alternately called northern sea oats, inland sea oats, wild or flathead oats – one glance, though, and it’s obvious where the common names come from. The flat flower spikelets that dangle merrily from long, arching stems recall what a good, hearty breakfast looks like before it’s reaped and boiled into mush. My very first glimpse of the grass was on a September morning (shortly after one such breakfast), when I spotted a number of the plants arranged in an autumn display at the entrance to a barn. Still in their black, No. 1 pots, the Chasmanthium drew my attention away from gourds and pumpkins and bales of hay that were intended to be the focus. I took home the grasses and left the other items behind.
Name: Chasmanthium latifolium
Common name: Northern sea oats; inland sea oats
Hardiness: Zones 4 to 9
Mature height: 24 to 48 inches
Mature spread: 12 to 24 inches
Classification: Ornamental grass
Landscape Use: Mid- to back of a mixedperennial border; prairie garden; focal point
Ornamental Characteristics: Clump forming; bright green to blue-green, graceful, narrow, straplike foliage; scaled seed heads that resemble oats bob on slender, arching spikes. Autumn color is light brown; dried seeds glow when backlit
Sea oats has a tendency to distract one like that. At this time of year, colorful shrubs and hardwoods dominate with their fiery leaves, drawing one’s attention to the brilliant reds and golds that set autumn skies ablaze. Chasmanthium’s autumn presence is not spectacular; both leaves and seed heads turn gradually to a soothing, soft brown, blending gracefully into the patchwork of fading foliage of companion plants. Nonetheless, this is when sea oats really shines.
During summer, the narrow, blue-green foliage forms a pleasing clump, spreading about 1 to 2 feet and eventually reaching 2 to 4 feet tall. The green spikelets then are nearly camouflaged among the leaves, but begin to turn ivory before their final resting color. Once fall settles in and the light begins to change, the drying seed heads appear to glow when backlit by a fading sun.
Ornamental grasses can add the delightful element of sound in the garden, and Chasmanthium is no exception. Sea oats’ contribution to the song, however, is a bit different from the distant and dreamy swish most grasses provide. Instead, the oatlike pendants issue a chattering, clattering clack, as if to add a bit of percussion. It’s at once a happy, upbeat sound and the signal of a plant settling down for the winter.
Even in the coldest months, Chasmanthium has something to offer. The “oats” persist, although the foliage may appear a bit raggedy and several of the spangles may begin to drop. Just when the plant looks really tired – late winter or early spring – it’s a good time to cut it back to its base.
Chasmanthium is low maintenance, happiest when it’s given a bit of shade, an occasional drink of water and average, decent soil that is well-drained – although it tolerates compacted soil, too. It’s not picky, and if it becomes too comfortable, it can reseed vigorously. Birds and small mammals may help to prevent aggression, but if its generous nature is to be curbed, trim the seed heads in fall and use them in flower arrangements. Deer browsing is rarely a problem.
Propagation is handily done by seed, which should be collected in fall, or by root division. If volunteers are discovered where they’re not welcome, they can be transplanted easily.
A plant need not wow one to become a favorite. In fall, when brilliant colors can be glorious – but blinding – Chasmanthium latifolium offers a sweet, sometimes amusing alternative.
Editorial Director, Horticulture Group