Vernonia fasciculata aka Common Ironweed

Vernonia fasciculata is a perennial in the daisy family, Asteraceae. Gardeners know it as prairie ironweed or smooth ironweed. Its native range runs from south-central Canada into the United States. It grows in the central and eastern parts of that country. In its native habitats, it grows in bright, moist places. It is not native to Britain or Ireland.

The plant forms clumps with tall stems that stand upright. RHS gives a height of 3.3–4.9 feet [1–1.5 metres]. Chicago reports plants about 6 feet [1.8 metres] tall and wide. Plants stay somewhat smaller where they receive more shade. RHS gives a narrower spread of 0.3–1.6 feet [0.1–0.5 metres]. These accounts show a wide range in garden size. The smooth stems carry deep green leaves at even intervals. Each leaf has a lance shape and a toothed edge. The plant sheds its leaves rather than keeping them year-round.

Small purple to violet flowers grow in tight groups. Branched stems hold these groups above the leaves. Chicago lists bloom from July through October. RHS places flowering in autumn, so timing varies between these accounts. Rust-red seedheads follow the flowers and add a later feature. The flowers draw butterflies, and the plant also attracts birds. Deer resistance adds to its value in gardens with browsing animals.

Give prairie ironweed moist soil and a site in full sun. It also accepts partial shade, though full sun is preferred. RHS recommends light soil with a moderate level of fertility. It lists clay, loam, sand, and chalk as suitable soils. Acid, neutral, and alkaline soils are all within its range. It accepts both moist, well-drained ground and sites with poor drainage. Chicago gives USDA zones 4–9, while RHS rates it H7. RHS lists two to five years to reach mature size.

Use its height at the back of a flower border. It also suits screens, cottage gardens, native gardens, and wildflower meadows. Maintenance needs are low, but it can become weedy. It seeds freely unless spent flowers are removed. Removing them can also help extend the bloom season. Propagate plants from seed or divide established clumps. Slugs and leaf miners may cause damage. RHS reports few disease concerns, and Missouri Botanical Garden reports no serious pest or disease problems.