Helianthus angustifolius aka Swamp Sunflower

Helianthus angustifolius is also known as swamp sunflower. It belongs to the daisy family. It grows wild in the north-central and eastern United States. Its range includes New York, Florida, and Texas. This herbaceous perennial has soft stems and lives for years. It forms clumps and sheds its leaves with the seasons. Gardens in colder areas sometimes grow it as an annual. Its name refers to its narrow leaves.

Garden plants reach about 5–8 feet [1.5–2.5 metres] tall. Full-grown clumps span about 3–5 feet [1–1.5 metres]. Plants can reach full size within one to two years. Rhizomes, or underground stems, help clumps spread, sometimes with force. The stems have hairs and are green, sometimes with purple tints. The narrow green leaves feel rough and have pointed tips. Each simple leaf has three veins that run lengthwise. Its edges are smooth. Leaves grow along the stems in an alternate pattern.

Yellow flower heads bloom from July until the first frost. Each head spans about 0.17–0.25 feet [0.05–0.08 metres]. Ten to twenty narrow rays ring the disk at its heart. This disk is often purple-brown, though some are yellow. Bracts with hairs sit beneath each head. Small fruits called achenes form from September to November. Insects, including butterflies, visit the flowers for nectar. The plant also serves as a host for silvery checkerspot caterpillars. Birds and small mammals eat its seeds.

Plants bloom best in full sun but tolerate some shade. They prefer moist soil and cope with wet spells. In drier sites, add enough water to keep them growing. They grow in sand, loam, clay, and chalk. NC State recommends acidic soil. RHS lists neutral to alkaline soil. RHS also calls for humus-rich soil that stays moist through summer. It rates the plant H6. NC State lists USDA zones 5–9. Tall stems may need stakes, most of all in wind. Prune in June to help stems branch. Divide clumps every two to four years to keep growth strong.

Use swamp sunflower behind shorter plants in beds or borders. It suits rain gardens, pond edges, and natural-style plantings too. Give clumps room to spread without crowding nearby plants. Caterpillars and beetles may chew leaves, but damage rarely needs treatment. Slugs and snails can cause trouble too. Plants may get rust, leaf spots, or powdery mildew. Sclerotinia diseases may also occur. NC State lists it as non-toxic to dogs, cats, and horses. The supplied sources do not confirm edible uses for people.