Chasmanthium latifolium aka Broadleaf Chasmanthium

Chasmanthium latifolium is a perennial grass in the Poaceae family. Gardeners know it as northern sea oats or river oats. Its native range runs from central Canada to northeastern Mexico. It also grows across the central and eastern United States. In the wild, it grows in rich woods and near streams. It forms upright clumps, then spreads through rhizomes and seeds.

Garden plants reach 2–5 feet (0.6–1.5 m) tall. Their spread reaches 1–2.5 feet (0.3–0.76 m). RHS gives a smaller range, reaching about 3.3 feet (1 m). Its listed spread reaches about 1.6 feet (0.5 m). Smooth, round, green stems carry flat, lance-shaped leaves. The leaves sit alternately along the stems and resemble bamboo leaves. They stand upright or bend outward in a slight arch. Fall brings yellow or copper tones, followed by brown in winter. The grass loses its leaves during the dormant season.

Small green flowers grow in open panicles on bending stems. Flat spikelets hang from the branches and move in breezes. Bloom records span June to October, with many sources noting late summer. Wind carries the pollen between flowers. The seed heads change from green to tan and purplish bronze. They remain on display through much of summer and fall. Each grain is a caryopsis, the fruit type of grasses. Birds and small mammals use the seeds as food.

Grow this grass in moist, fertile soil with good drainage. It also accepts soil that becomes wet at times. It grows in clay, loam, sand, and chalk. RHS lists acid, neutral, and alkaline soils as suitable. Full sun and partial shade both suit it. It also tolerates dappled shade beneath trees. Chicago lists USDA zones 3–8; NC State lists zones 5–9. RHS rates it H7 for UK conditions. Cut old growth back in late winter. Sow seeds in spring or divide clumps in early summer.

Use it in borders, woodland gardens, or broad natural plantings. It also suits containers, stream banks, and pond edges. Cut and dried flower heads add shape to arrangements. The grass hosts northern pearly-eye and several skipper caterpillars. Deer tend to avoid it. Seeds and rhizomes can cause unwanted spread in small gardens. Some plants need support, though serious pests and diseases are uncommon. PFAF lists cooked seeds as edible, including ground seed for flour. It reports no known hazards and no known medicinal uses.