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Vernonia gigantea

tall ironweed

Asteraceae Eastern and central North America

Attracts Pollinators Attracts Butterflies Deer Resistant

Native to North America

SunFull Sun – Part Shade

WaterHigh

HardinessZones 5–9

Overview

Vernonia gigantea is an upright herbaceous perennial reaching 4-7 feet (1.2-2.1 m) tall, occasionally to 10 feet (3 m), forming clumps from a fibrous-rooted crown. Stems are erect, mostly unbranched until the inflorescence, smooth to slightly hairy, and often purple-tinted. Leaves are alternate, lance-shaped to narrowly elliptic, 4-10 inches (10-25 cm) long with finely toothed margins, green above and paler below. Flat-topped to open clusters of 15-30 small flower heads appear from August through October; each head holds 13-30 reddish-purple disk florets and no ray florets. Flowers give way to tufted, bristly seeds dispersed by wind. The plant spreads slowly by short rhizomes and self-seeds freely on bare ground. Lower leaves often brown and drop by flowering time in dry soils. Established clumps reach 2-3 feet (60-90 cm) wide. The tall, late-season stems may flop in rich soil or shade without support.

Native Range

Native to eastern and central North America, from Pennsylvania and Ohio south to Florida and Texas, and west to Nebraska. Grows in moist meadows, low woods, stream banks, ditches, and damp fields, usually in full sun on rich, moisture-retentive soils.

Suggested Uses

Planted in rain gardens, pond and stream margins, wet meadows, and the back of perennial borders at 24-36 inch (60-90 cm) spacing. The late flowers draw butterflies and native bees, suiting it to pollinator and naturalized plantings. Its height and self-seeding make it less suited to small, formal gardens.

How to Identify

Distinguished from Vernonia noveboracensis by its smaller flower heads with 13-30 florets and blunt, appressed involucral bracts rather than long, thread-like bract tips. Stems reach 4-7 feet (1.2-2.1 m), bearing alternate lance-shaped leaves 4-10 inches (10-25 cm) long. The reddish-purple disk flowers open in flat-topped to loosely branched clusters in late summer.

Appearance

Size & Dimensions

Height4' - 7'

Width/Spread2' - 3'

Colors

Flower Colors

purple

Foliage Colors

green

Bloom Information

Bloom Period

~5 weeks

Summer Fall

Blooms from August through October, peaking in September. Each clump flowers for about 4-5 weeks. The reddish-purple heads open from the cluster edges inward. Bloom is reduced in shade and on dry soils.

Detailed Descriptions

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 6-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.0(Neutral)

357912

Soil Types

clay loam silt

Drainagemoist

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

2-3 years

Care & Maintenance

Care Guide

Grows in full sun to light shade in moist to wet, fertile soils and tolerates seasonal flooding and heavy clay. Water during establishment and in drought; dry soil shortens the plant and causes early leaf drop. Stems grow shorter and sturdier in full sun and lean soil, and taller and weaker in shade or rich ground. It self-seeds readily, producing many volunteer seedlings unless seed heads are removed. Few serious pests occur, though rust and leaf-mining insects may mark the foliage in late summer. Divide crowded clumps in spring every 3-4 years to maintain vigor.

Pruning

Cut stems to the ground in late fall after frost or in early spring before new growth. Cutting plants back by one-third in early summer reduces height and the tendency to flop, delaying bloom by 1-2 weeks. Removing spent flower heads before seeds ripen limits self-seeding.