Helianthus occidentalis aka Western Sunflower

Helianthus occidentalis is a perennial wildflower in the daisy family. Its common names include western sunflower and naked-stem sunflower. It comes from the central and eastern United States. Despite its name, it is not a western native. It grows in prairies, glades, dry meadows, and open rocky woods. It also occurs along rocky or sandy river margins.

Most plants reach 2–3 feet [0.61–0.91 metres] in garden settings. Some reach 4 feet [1.22 metres]; another source lists 5 feet [1.52 metres]. Plants spread 1.5–2 feet [0.46–0.61 metres] before forming larger colonies. Long-stalked leaves form a low clump at the base. These green leaves feel rough and have paler undersides. Their shapes range from oval to long and narrow. Leaf edges may be smooth or have small teeth. Upright flower stems carry few leaves, giving them a bare look. The stems range from green to reddish green, with variable hairiness. Shallow rhizomes let the plant spread beyond its first clump.

Each stalk bears one to twelve flower heads. The heads measure about 1.5–2.5 inches across. Yellow to orange-yellow rays surround a yellow disk of tiny florets. Bloom runs from summer into early fall. Missouri Botanical Garden lists August through September. Chicago Botanic Garden gives a wider July through October season. A colony may flower for about a month. Brown, dry fruits appear from August through November. Each fruit holds one seed and is called a cypsela. NC State lists the fruit as edible. The evidence gives no further details on eating it or toxicity.

Give this sunflower full sun and soil that drains well. It accepts partial sun but prefers a sunny site. Dry to moderately moist soil suits it. It tolerates drought, poor sand, loam, and amended clay. Avoid heavy clay without improving it first. It accepts acidic, neutral, and alkaline soils. Sources place it in USDA zones 4–8. Divide plants every three or four years to limit spread. Division also helps keep clumps vigorous.

Use it in borders, native gardens, or prairie plantings. Its roots help hold dry soil against erosion. The flowers suit cutting and draw butterflies and other pollinators. Birds also visit the plants. Silvery checkerspot caterpillars use it as a host. Sources report no major pest or disease concerns. Taller stems may need stakes for support. It spreads, but NC State calls it less aggressive than other sunflowers.