Helianthus microcephalus aka Woodland Sunflower

Helianthus microcephalus has the common name small woodland sunflower. It belongs to the aster family, Asteraceae. This plant lives for years. It comes from the east-central and southeastern United States. It grows in dry woods and beside roads. In North Carolina, most grow in Piedmont and mountain areas. Its upright stems form a tall, bushy clump. Garden plants often reach 4–6 feet [1.2–1.8 metres]. RHS gives a taller range, reaching 8.2 feet [2.5 metres]. Clumps spread about 2–4 feet [0.6–1.2 metres] wide.

The smooth stems range from green to reddish green. Narrow, green leaves taper to a point. Their upper sides feel rough and bear resin dots. Soft hairs form tangles on parts of the leaf undersides. Leaf edges may be smooth or toothed. Lower leaves grow in opposite pairs along the stems. Higher leaves grow one at a time, not in pairs. The plant sheds its leaves at the season's end.

Yellow flower heads bloom from July through October. Each head has rays around small disk flowers at its centre. Heads may grow alone or in groups. Bees and butterflies come to the flowers for food. The leaves also feed the young of several butterfly kinds. These caterpillars include painted ladies, spring azures, and silvery checkerspots. Groups of achenes, the dry fruits, form from September through November. Birds eat the seeds, so the plant has value after bloom.

Grow this sunflower in sun, though it accepts some shade. It grows in clay, loam, or sandy soil. Soil must drain well, even when it stays moist. Once rooted and settled, plants withstand drought and spells of dry soil. RHS favours soil rich in humus, with a fair level of nutrients. Sources support acid, neutral, and alkaline soils. NC State lists USDA zones 4–8. RHS lists H2, a rating for much less cold tolerance. The sources thus differ sharply on how much cold it withstands.

Use it in borders, cottage gardens, or native plantings. Its long bloom season also suits gardens for pollinators. Rhizomes, or spreading stems, and dropped seed can extend a planting. RHS calls it non-invasive. But NC State says to keep unwanted spread in check. Remove spent heads to curb new seedlings and prompt more flowers. Divide clumps when needed to keep their growth in check. Sow seed in spring or divide plants in autumn. Leave seed heads for birds, or cut stems in autumn. Watch for aphids, cutworms, and weevils, plus slugs and snails. Rust, leaf spots, mildews, and fungal rots may cause disease.