How to Grow and Care for Northern Sea Oats

Northern sea oats grass with light brown flower heads and lance-shaped leaves

The Spruce / Evgeniya Vlasova

Northern sea oats is a perennial ornamental grass that can be planted in late spring (after the threat of frost has passed) or in the fall. It is a member of the Poaceae family, making it a true grass. In some regions, it is a vigorous enough spreader to be considered invasive. The first shoots in spring are blue-green. An established plant will have grown 2 to 3 feet high by mid-summer, displaying loose clumps of green foliage. The leaf blades are lance-shaped, arching, and bear a mid-green color.

Warning

Northern sea oats can spread both through seeds and rhizomes. It is rarely invasive in the northern United States, but, in warmer climates, it may be invasive. Check with your county extension if you want to find out if it is considered invasive in your area. One way to minimize the chances of its spreading is to grow it on a patio in a container.

By late summer, it begins to bear panicles of its namesake oat-like, green flower heads, which are its chief ornamental feature. Not only are these flower heads visually appealing with their jagged edges, but they also flutter in the wind, creating a rustling sound that adds interest to the landscape.

But while the plant does afford summer interest, northern sea oats comes into its own in fall. This is when the flower heads begin to ripen into seed heads and change to a bronze color. As fall progresses, the leaf blades change to a golden color to complement the seed heads. Although the foliage color eventually fades to a tan color, the plant continues to offer landscape interest in winter.

 Common Names Northern sea oats, indian wood oats, inland sea oats, river oats, wild oats, wood-oat
 Botanical Name Chasmanthium latifolium
 Family Poaceae
 Plant Type Herbaceous perennial
 Mature Size 2 to 3 ft. tall and wide
 Sun Exposure Full sun to partial sun; will survive in partial shade
 Soil Type Well-drained loam adequately irrigated, with good fertility
 Soil pH Neutral to slightly acidic
 Bloom Time Late summer
 Flower Color Green
 USDA Hardiness Zones 5 to 9 (USDA)
Native Areas Eastern United States and Northern Mexico

Northern Sea Oats Care

Since northern sea oats provides winter interest, leave it standing all winter. Cut the stalks down to within a few inches of the ground in spring, to ready the spot for the new shoots. Mulch the plant if you live where it is only borderline hardy. For example, some gardeners have been successful growing it in zone 4 if they mulch, even though the plant is listed as being cold-hardy only as far north as zone 5.

Locate northern sea oats in a spot where it can be accompanied by other plants that enjoy the same growing conditions and that can complement it. For example, northern sea oats can provide a contrast in texture with compatible plants that have wider leaves, such as Rodgers flower (Rodgersia aesculifolia).

A row of northern sea oats plants also makes for a great backdrop to a bed of shorter plants.

Northern sea oat grass with jagged brown and green flower heads closeup

The Spruce / Evgeniya Vlasova

Northern sea oat grass with arching stems, green leaves and brown jagged flower heads closeup

The Spruce / Evgeniya Vlasova

Northern sea oat grass stems arching with brown flower heads closeup

The Spruce / Evgeniya Vlasova

Northern sea oat grass with brown jagged flower heads and yellow-green leaf blades

The Spruce / Evgeniya Vlasova

Light

Give northern sea oats full sun to partial sun. While it will survive if grown in partial shade, it will not thrive to the same degree: Flowering will be reduced, and its fall color will not be as strong. This is an important consideration since northern sea oats is grown mainly for its flower heads and for its fall color.

However, the more sun it receives, the more water you should give it; so be prepared to provide it with more care (irrigation) if you are growing it in an area with full sun. If low-maintenance landscaping is more important to you than optimal performance, grow it in partial sun so that you can cut back on watering. At the southerly end of its range, the summers are so hot that it is best to grow northern sea oats in partial sun or even in partial shade.

Soil

Northern sea oats likes well-drained, fertile ground. A loamy soil fortified with compost is ideal.

Water

Northern sea oats has only moderate moisture needs if grown in partial sun or partial shade, but it does not like for its soil to dry out completely. Aim for a consistently moist soil, especially during the heat of summer.

Temperature and Humidity

Northern sea oats performs best in climates with moderate summer heat and humidity. It does not perform well in the Deep South, which is why the most southerly USDA zone it is listed for is zone 9.

Fertilizer

Northern sea oats needs a fertile soil to perform optimally, so feed it annually with compost or manure tea.

Types of Northern Sea Oats

Chasmanthium latifolium is one of five species of Chasmanthium, but the other four are not as commonly grown. The other four species are:

  • Chasmanthium nitidum (shiny wood-oats)
  • Chasmanthium ornithorhynchum (bird-bill wood-oats)
  • Chasmanthium sessiliflorum (long-leaf wood-oats)
  • Chasmanthium laxum (slender wood-oats)

But some nurseries and online catalogs do carry a variegated leaf cultivar of Chasmanthium latifolium known as 'River Mist'. As with many variegated plant cultivars, it likes a little more shade than the species plant.

Propagating

The best (easiest) way to propagate northern sea oats is through division. Divide and transplant it any time between mid-spring and early summer. Do not let its soil dry out completely during this operation.

How to Grow Northern Sea Oats From Seed

Northern sea oats is also easy to start from seed. No special steps are required to get its seed to germinate. You can either collect the seed in fall or buy it; the seed is readily available for sale online.

Common Pests and Plant Diseases

Northern sea oats is bothered by few pests or diseases. Most importantly, the deer leave it alone; because of their size (and thus their ability to eat so much), deer, where they are present, are typically the landscaper's worst nightmare.

How to Get Northern Sea Oats to Bloom

Provided that they have been planted in full sun, northern sea oats will readily start blooming in the late summer each year, with little extra help from you. The flower head, which imperceptibly morphs into a seed head in fall, measures about 1 inch long and wide; it is razor-thin. For optimal flowering, simply keep the soil evenly moist and give the plant an annual feeding. Since the flower head is the main draw of the plant, do not deadhead.

FAQ
  • Is northern sea oats salt tolerant?

    Yes, which makes it a good choice if you garden in seaside communities or if you are landscaping along a road that the town salts in winter.

  • Is northern sea oats drought resistant?

    It is moderately drought tolerant once established, in the sense that a mild drought will not kill it. However, northern sea oats will not perform optimally without adequate irrigation.

  • How can you use northern sea oats?

    Cut some stems of northern sea oats and use them in dried floral arrangements.