Dictionary of Flowers: Chasmanthium Latifolium (Northern sea grass, Northern sea oats)

Chasmanthium Latifolium in their dried phase. Image used under a Creative Commons licence with the kind permission of janetandphil and Flickr
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Chasmanthium Latifolium in their dried phase. Image used under a Creative Commons licence with the kind permission of janetandphil and Flickr

  • Chasmanthium Latifolium
  • Common name: northern sea grass, northern sea oats
  • Family: Poaceae
  • Category: Perennial in USDA zones 3 to 8
  • Height: 24” to 5’
  • Width: 12” to 30”
  • Sun/part shade
  • Blooms: late summer to early fall
  • Attracts: birds
  • Growth habit: Upright, clump forming. Used as a thriller in container combinations
  • Maintenance: medium
  • Soil: average, moist, free draining. Water regularly if grown in containers. 
  • Garden uses: containers, mixed border, mass planting
  • Diseases: fairly disease resistant
  • Pests: no pests

Native to the United States and Mexico, Northern sea grass is one of the most shade tolerant ornamental grasses.

It forms green clumps of foliage during late spring and early summer, but its ornamental value comes when the seed heads form. They are green, oat like, dangling from thin, long, arching stems.

The seedheads turn from green to tan to bronze as summer progresses. The foliage also turns bronze in fall, adding interest to the garden. Birds love the seed, so it will attract sparrows and finches to the garden. 

Chasmanthium does well in average to fertile, moist but free draining soils. It can tolerate some drought once established.

Prefers a full sun to part shade position. In northern zones, it needs to be cut back after the hard frost and it is somewhat slow to start growing again. In warm zones, it can be cut back in spring before the new growth begins.

Cut it back to two inches. In the coldest of zones, it is a good idea to provide a mulch cover during the winter months.

Northern sea grass is propagated by division or seed. It can reseed itself quite aggressively. To divide, separate clumps in late spring and replant divisions.

Early season green Northern Sea Oats. Image used under a Creative Commons licence with the kind permission of Andrey Zarkikh and Flickr
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Early season green Northern Sea Oats. Image used under a Creative Commons licence with the kind permission of Andrey Zarkikh and Flickr

It is a warm season grass, so in order for a good root system to develop, it's best to plant when soil is warm. It doesn't require much fertilizer; a top dressing of compost in spring when it starts growing is normally sufficient.

It is available as plants in nurseries during spring and summer. Easy to grow from seed, it can be started indoors six to eight weeks before last frost. Press seeds into moist starting mix and cover with a very thin layer of mix.

At 70-75F, it germinates in ten to fifteen days. Once the seedlings emerge, when they reach one inch, thin them.

Wait to place them in their permanent location until the soil is warm, in late spring. The seed can also be sown outdoors a couple weeks after the last frost date.




Northern Sea Grass, aka Chasmanthium Latifolium. Image used under a Creative Commons licence with the kind permission of Josiah Lau and Flickr
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Northern Sea Grass, aka Chasmanthium Latifolium. Image used under a Creative Commons licence with the kind permission of Josiah Lau and Flickr

Chasmanthium is pretty resistant to disease and pests. It is also not appealing to deer.

Popular varieties:

  • Chasmanthium latifolium - the most commonly sold of the species
  • Chasmanthium latifolium 'River Mist' -variegated variety, up to thirty six inches tall
Dry drama, Northern Sea Oats-style. Image used under a Creative Commons licence with the kind permission of Kristine Paulus and Flickr
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Dry drama, Northern Sea Oats-style. Image used under a Creative Commons licence with the kind permission of Kristine Paulus and Flickr

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