Helianthus maximiliani aka Maximilian Sunflower

Helianthus maximiliani, or Maximilian sunflower, belongs to the daisy family. This perennial wildflower grows from Canada to northeast Mexico. It grows in prairies, beside roads, and on bluffs. It also occurs on waste ground. Its name honors Prince Maximilian, who explored the Great Plains. The plant forms upright clumps and spreads through rhizomes. It can also seed itself and form large colonies.

In gardens, plants reach about 5–8 feet (1.5–2.5 m) tall. North Carolina State reports a wider range of 2–10 feet (0.6–3 m). Clumps spread about 3–5 feet (1–1.5 m) wide. Growth is fast. The stiff stems bear short hairs and stay mostly unbranched. Their color ranges from green to purple. Long, narrow leaves have pointed tips and a rough feel. Fine white hairs cover their upper sides. Leaves may fold along the midrib and turn purple in fall. The plant sheds its leaves for winter.

Yellow flower heads open from August to September. They grow at stem tips and in leaf axils. Each flowering stem carries at least four heads. Most heads span about 0.17–0.33 feet (0.05–0.10 m). Yellow rays surround a darker yellow disk of small florets. The flowers have a scent and suit cutting. Dry fruits follow in fall, each holding one seed. Birds, squirrels, and gophers eat the seeds. Bees and butterflies visit the blooms for nectar. The plant also hosts Silvery Checkerspot caterpillars. Livestock and some wild mammals graze its leaves. The supplied sources do not establish human edibility or toxicity.

Grow this sunflower in full sun with good soil drainage. It accepts clay, loam, sand, and rocky ground. Soil may range from dry to moderately moist. The RHS favors humus-rich soil with neutral to alkaline pH. Established plants withstand drought, and deer tend to leave them alone. Sources give USDA zones 4–9 and the UK rating H4. Tall stems may need stakes, especially in exposed sites. Grow new plants from seed or by dividing clumps. Divide established clumps every two to four years to maintain vigor. Cut old stems back as they die after flowering.

This tall sunflower suits meadows, prairie plantings, and native gardens. It also fits cottage borders and wildlife gardens. Mass plantings provide late flowers and seed for birds. Its spread needs space where colonies can develop. North American sources report few serious pest or disease problems. The RHS lists slugs and snails as possible pests. Powdery mildew and sclerotinia diseases may also occur.