Vernonia gigantea aka Tall Ironweed

Vernonia gigantea, or giant ironweed, belongs to the daisy family. This perennial wildflower grows in central and eastern North America. Its native range includes southeastern Canada and much of the United States. It grows in meadows, prairies, low woods, and stream margins. It also occurs in floodplains, roadside sites, and grazed pastures. Livestock avoid its bitter leaves, which helps it spread in pastures.

Garden plants often reach 5–8 feet [1.5–2.44 metres] tall. North Carolina Extension gives a shorter range of 3–5 feet [0.91–1.52 metres]. Some plants reach 10–12 feet [3.05–3.66 metres]. Mature plants can spread to 6 feet [1.83 metres]. Stiff stems rise straight up and branch near the top. They range from light green to green with purple tones. Their surfaces may be smooth or hairy. Alternate leaves have toothed edges and vary in shape. Their upper sides are dark green; their undersides are paler. Some leaves have fine hairs beneath.

Flat, branched clusters carry the flowers above the leaves. The blooms range from lavender and magenta to deep purple. Each small flower head contains 10–30 tubular florets. These heads lack the ray flowers found on many daisies. Flowering runs from late summer into fall. Chicago Botanic Garden lists a July–October bloom window. Bees and butterflies visit the flowers. Gray-brown achenes form after bloom, each with a tuft of hairs. Wind carries these small fruits away from the plant. Dead hollow stems also provide nesting sites for native bees.

Grow giant ironweed in full sun or partial shade. It prefers moist to wet soil but handles ordinary garden soil. It tolerates brief flooding and a broad range of soil pH. Loam, clay-loam, and sandy-loam all suit it. Moist soil can lead to taller growth. Chicago Botanic Garden lists the species for USDA zones 3–8. Cutting stems back in late spring can limit height. Plants grow readily from seed or division. Removing spent flower heads can reduce unwanted seedlings.

Its height suits the rear of borders and meadow plantings. It also fits cottage, native plant, and pollinator gardens. Deer tend to leave it alone. It can compete with nearby plants and become weedy. The sources report no major pest or disease problems. Aphids may feed on stems and leaves. Some moth caterpillars feed on stems and roots. Crickets and katydids may eat the flower heads. Giant ironweed can hybridize with other native ironweeds, making identification harder.