chasmanthium, a native grass for shade

Northern sea oats, upland or inland sea oatsIN THE WAY THAT PINE CONES fascinate me, I’m taken in by the seedheads of Northern sea oats, too—and actually, they’re a little bit like a flattened cone, aren’t they? One of three shade-tolerant ornamental grasses I grow, Chasmanthium latifolium is an American native. Chasmanthium latifolium, up close:

Northern (also called upland, or inland) sea oats is native to Eastern North America, says the Lady Bird Johnson Wildflower Center, specifically “from PA south to n. FL, west as far as s. IL, e. KS, and central TX,” and into northern Mexico. It’s easy to grow, and some birds enjoy its seeds, as do small mammals. Me, too.

Chasmanthium likes a semi-shady to shady spot where the soil is moist, and it can even take poor drainage. This is a low-maintenance plant suited to that hardest of spots–a shady slope—because sea oats forms strong, widening clumps, and also reseeds (some gardeners in certain locations say it does that too much; not true here). Don’t plant it in baking sun (I have had it do well in half-day sun where the soil moisture was good), and give it a bed of its own, or with other strong growers.

Its slightly blue-green foliage, which resembles a low bamboo’s and by high summer is more green than blue, sprouts early in springtime, reaching about 2 feet tall for me (and taller in some environments), arching and attractive. In fall the foliage goes bright yellow, at about the same time the seedheads (which start off green in summer, and fade to pale tan, bouncing all the while on wiry stems) go bronzy-coppery tones before turning brown. I leave the plants up in winter, to get the most from the display and any wildlife value, and clean them up during a thaw in February or March—the same way I treat bigger Asian ornamental grasses such as Miscanthus and Pennisetum.

Wondering what my other shade-tolerant ornamental grasses are? Gleaming golden Hakonechloa macra ‘All Gold’ is one (knee-high, part shade), and the thuggish green-and-white showy one called gardener’s garters that I’ve had 20 years and managed to keep in one little spot somehow, Phalaris arundinacea ‘Picta.’

  1. Alejandro says:

    I planted mine in a mixed border where it looked great. The problem I had with it was the thousands of babies sprouting everywhere including the crowns of other perennials. Next time I’ll use it I’ll follow your advice on where to grow it. Thank you.

  2. Helen says:

    I had the same experience as Alejandro. Planted in a mixed bed with other grasses it thrilled us for a year–and has driven us crazy ever since. We took out all of the original planting but are still, four years later, pulling baby plants out of the Japanese blood grass and the liriope. I can see where it would look great on a tough but shady slope but it is definitely a no no for smaller gardens, lovely as those seed heads are.

    1. margaret says:

      Hi, Helen. Doesn’t sow a lot here — actually, I have lost the plants entirely once and had to start over in one spot where I use them. Fascinating!

  3. I love this grass and it is on my wish list. I’m not sure if it is hardy to Z4. Some say yes, some say Z5. I would hate to have a nice drift of this and then lose it one year (like my sniff, Oakleaf Hydrangea). I am also looking into shade-tolerant sedges for my area like Carex Plantaginea. I think my goal is to remove ALL of my lawn.

  4. Barbara Robinson says:

    I have this growing in the deepest shade I have and it does not take over. It is so nice to have a grass that grows in shade. Another one I really like for a woodland setting is Carex pensylvanica. It makes a wonderful soft ground cover under trees.

  5. Kae in WNC says:

    I love the idea of native grasses but I want them for shady areas in my pasture for my Scottish Highland cattle. Do deer like the plant or is it just the seedheads that attract wildlife?

  6. Gigi says:

    I’ve had Chasmanthium in my Cascade Mountain garden for several years now and it laughs at the cold as well as the heat. It takes longer to get going, but is well worth it in colder climates. And, yes, lovely in the fall!

  7. jamie says:

    speaking of pine cones, what are you favorite and have you done a story on them? I am using the sugar and jeffery’s this year but would love some cool big pine cone suggestions. Thanks, jamie

    1. margaret says:

      Hi, Jamie. I haven’t written about them and don’t have much variation here (nothing too big, really), but what a great idea, thank you.

  8. john says:

    This plant is very invasive (well, it’s native so let’s call it aggresive) here in western PA. In the words of Allan Armitage :”we have a few plants of our own that wear invasiveness with pride, and this is one of them.”

  9. Linda says:

    I love this grass, but it spreads far too aggressively around here to consider adding it to our garden. I have a nice bunch of seed heads indoors in a vase, and as much as I love this grass, that’s as close to our garden as it will ever get!

  10. betsyohs says:

    I would love to hear an update on this plant – do you still have it? Is it still not very aggressive in spreading? I love the seed heads and am thinking about planting some in my shady, sloped, southern VT garden, but I don’t want it to go everywhere.

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