A tall, erect, clump-former. Lance-shaped, deep-green leaves. Fluffy, rose-purple, small flower heads occur in large, loosely branched, flat-topped, terminal clusters. Flowers give way to rusty seed clusters. An aggressive reseeder. Larval host for American painted lady butterfly. Special value to native bees.
Differs from V. noveboracencis not only with a shorter height, but in that the leaves, stems and flower heads are distinctively glabrous (smooth and lacking hairs), thus the alternate common name of smooth ironweed. Somewhat suggestive of Joe Pye weed before bloom, except leaves of ironweed are alternate and those of Joe Pye weed are whorled.
V. fasciculata tends to hybridize with other native ironweeds, which can sometimes complicate plant identification.
Tolerates wide range of soils, but prefers rich, moist soils. Generally grows taller in moist soils. Remove flower heads before seed develops to avoid unwanted self-seeding (although birds do eat the seeds – a conundrum which I wrestle with myself). Overall plant height may be reduced by cutting stems back nearly to the ground in late spring.
Height: 2-4 ft.
Spread: 1.5-3 ft.
Bloom time: July to September
Sun: full sun
Water: medium to wet
Naturalize, rain garden
photo credit: Krzysztof Ziarnek, Kenraiz