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A Comprehensive Guide to Giant Ironweed (Vernonia gigantea)

Giant Ironweed (Vernonia gigantea) is a herbaceous perennial that is native to the eastern and mid-western United States and the province of Ontario in Canada. This plant is a host to the American Lady butterfly (Vanessa virginiensis). Growing from 2.5 to 10 feet tall, this species grows in floodplains, and has purple flowers that bloom from June to September. This plant is hardy in zones 5-8.

Taxonomy and Naming of Giant Ironweed (Vernonia gigantea)

Herbarium specimen of giant ironweed (Vernonia gigantea).
Herbarium Specimen — Vernonia gigantea (Walter) Trel. collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)


Giant Ironweed (Vernonia gigantea) was named and described by Thomas Walter, an American botanist in 1788 as Chrycosoma gigantea. Later in in 1891, William Trelease, changed the genus to Vernonia. It has kept the same name since and is a member of the Aster Family (Asteraceae).

Meaning of the Scientific and Common Names

Scientific Name

The genus name, Vernonia, is in honor of William Vernon, an English botanist. The species name, gigantea, is Latin for giant and refers to the size of the plant.

Common Name and Alternative Names

The common name derives from the large size of the plant. Another common name, tall ironweed, is of similar derivation. Some sources just call this plant “ironweed.”

Physical Description of Giant Ironweed (Vernonia gigantea)

Close-up of purple flower of giant ironweed (Vernonia gigantea).
Flower of Giant Ironweed (Vernonia gigantea) — Andy Wilson, CC0, via Wikimedia Commons


  • Plant Type: This plant is a herbaceous perennial.
  • Height: This plant is 2.5 to 10 (12) feet tall.
  • Stem: The stems are erect and slightly pubescent below and more pubescent above (Urbatsch 1972).
  • Leaves: The leaves are mostly cauline, alternate, simple, have serrate margins, and lanceolate in shape. The leaves are 4.5-12 inches in length and 0.8-3 inches in width.
  • Flower color: Purple to pink
  • Blooming period: This plant blooms from June to September.
  • Fruiting type and period: This plant has achenes that mature in the late summer to fall.

Range of Giant Ironweed (Vernonia gigantea) in the United States and Canada

Range map of giant ironweed (Vernonia gigantea) in the United States and Canada.
Range Map Credit: Kartesz, J.T., The Biota of North America Program (BONAP). 2023.(website Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2023. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)]

This ironweed is native to the mid-western and eastern United States, except New England and New Jersey, and the province of Ontario in Canada. It is considered to be rare in the states of Texas, Kansas, North Carolina, Maryland, New York, and the province of Ontario.


Meadow habitat in Europe.
Meadow Habitat — Leonhard Lenz, CC BY-SA 4.0, via Wikimedia Commons

This species grows in floodplains (Flora of North America and Hoagland and Jones 1992), meadows (Botanical Survey of Nebraska 1892), stony pastures (Peck 1902), maritime forest (Zomlefer, et al 2007), woodland borders (Thompson and Jones 2010), pastures (Pound and Clements 1900), dry sandy woods (Earle 1902), and low wet places (Urbatsch 1972).

Hosted Insects

American lady butterfly on moist ground.
American Lady Butterfly (Vanessa virginiensis) — ALAN SCHMIERER, CC0, via Wikimedia Commons

This species is a host for the American Lady Butterfly (Vanessa virginiensis). Some moths also feed on this species including the Ironweed Borer Moth (Papaipema cerussata) and the Red Groundling Moth (Perigea xanthoides) (Wikipedia).

Other Supported Wildlife

Honeybee on purple flower.
Purple Aster with Honeybee — John Severns (Severnjc), Public domain, via Wikimedia Commons

This species is a nectar source to other butterflies, skippers, bees, and wasps during the growing season. Species specifically noted for using this plant include the Horace’s duskywing (Erynnis horatius), whirlabout (Polites vibex), white peacock (Anartia jatrophae) (Minno 1992), the diana fritillary (Speyeria diana) (Gatrelle 2021), gulf fritillary (Argaulis vanillae), the cloudless sulphur (Phoebis sennae) (May 1985), and the great spangled fritillary (Speyeria cybele) (Rudolph, et al 2006).

Frequently Asked Questions about Giant Ironweed (Vernonia gigantea)

Is this plant poisonous?

This plant is not listed as being poisonous.

Does this plant have any ethnobotanical uses?

The Native American Ethobotanical Database does not cite this species specifically, but ironweeds in general, have been used as anti-diarrheal drug.

How is this plant distinguished from other Ironweeds?

This species is similar to prairie ironweed (Vernonia flaccidifolia), but the pubescent stem separates it from it. It is also similar to Missouri ironweed (Vernonia missourica) and western ironweed (Vernonia baldwinii) in having pubescent stems, but the scabrellous leaves and lack of gland-dotting separates it from both (Flora of North America).

Is this plant invasive?

This plant has been described as being weedy in meadows (Adams and Thompson 2017) and in pastures (Jones 1982).

Is this plant deer resistant?

This species contains chemicals, called sesquiterpene lactones, which give a bitter taste and repel herbivores (Burnett, et al 1977). These chemicals make this species resistant to most browsing.

Gardening with Giant Ironweed (Vernonia gigantea)

Add Giant Ironweed to Your Garden

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Purplish-pink flowers of giant ironweed (Vernonia gigantea).
Flowers of Giant Ironweed (Vernonia gigantea) — Cbaile19, CC0, via Wikimedia Commons


This species is hardy in zones 5-8. If your garden is within these zones and you have the right growing conditions (soil, moisture and exposure), you may well be able to grow this plant. However, if planted outside of its range, the hosted species may not recognize the plant or be harmed by ingesting a different species with an unfamiliar chemical composition.

Optimal Conditions

This species grows in full sun in medium to moist soil. In a garden this species can handle drier conditions and partial-sun.


  • Adams, Christopher A. and Ralph L. Thompson. 2017. Ecology of an Endangered Gentiana flavida Population in East-Central Kentucky. Phytoneuron 2017-83: 1-25.
  • Botanical Survey of Nebraska. 1892. I. Preliminary: The Plan and Scope of the Survey. Lincoln, NE: Botanical Seminar of the University.
  • Burnett, William C., Samuel B. Jones, and Tom J. Mabry. 1977. Evolutionary Implications of Sesquiterpene Lactones in Vernonia (Compositae) and Mammalian Herbivores. Taxon 26: 203-207.
  • Earle, Franklin Sumner. 1902. The Flora of the metamorphic region of Alabama. Bulletin of the Agricultural and Mechanical College of Alabama No. 119.
  • Gatrelle, Ronald R. 2021. Taxonomic Report of the International Lepidoptera Society. v. 9 No. 9.
  • Hoagland, Bruce W. and Ronald L. Jones. 1992. Wetland and Riparian Flora of the Upper Green River Basin, South-Central Kentucky. Transactions of the Kentucky Academy of Science 53(3-4): 141-153.
  • Jones, S.B. 1982. The genera of Vernonieae (Compositae) in the southeastern United States. Journal of the Arnold Arboretum 63: 489-507.
  • May, Peter Gregory. 1985. Foraging selectivity in adult butterflies: morphological, ecological, and physiological factors affecting flower choice. University of Florida Ph.D Dissertation.
  • Minno, Marc C. 1992. Butterflies of the Archbold Biological Station, Highlands County, Florida. Journal of the Lepidopterists Society 46: 138-158.
  • Peck, Charles H. 1902. Report of the State Botanist 1901. Bulletin of the New York State Museum v.10 no.54.
  • Pound, Roscoe and Frederic E. Clements. 1900. Phytogeography of Nebraska, 1. General Survey by Roscoe Pound and Frederic E. Clements. (Lincoln, NE: Botanical Survey of Nebraska).
  • Rudolph, D. Craig, Charles A. Ely, Richard R. Schaefer, J. Howard Williamson, and Ronald E. Thill. 2006. The Diana Fritillary (Speyeria diana) and Great Spangled Fritillary (S. cybele) Dependence on Fire in the Ouachita Mountains of Arkansas. Journal of the Lepidopterists Society 60(4): 218-226.
  • Thompson, Ralph L. and Ronald L. Jones. 2010. Vascular Flora of the Old Mulkey Meeting House State Historic Site, Monroe County, Kentucky. Journal of the Botanical Research Institute of Texas 4: 391-409.
  • Urbatsch, Lowell E. 1972. Systematic Study of the Altissimae and Giganteae Species Groups of the Genus Vernonia (Compositae). Brittonia 24: 229-238.
  • Zomlefer, Wendy B., David E. Giannasi, and Walter S. Judd. 2007. A Floristic Survey of National Park Service Areas of Timucuan Ecological and Historic Preserve (including Fort Caroline National Memorial), Duval County, Florida. Journal of the Botanical Research Institute of Texas 1: 1157-1178.
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Robert Coxe

Robert Coxe

Robert Coxe is a professional ecologist and botanist who has worked as the State Ecologist of Delaware and as an ecologist for the Western Pennsylvania Conservancy. He is also a former Past-President of the Pennsylvania Academy of Science. He currently is an innkeeper at McMullen House Bed & Breakfast LLC and a web designer and owner for Silphium Design LLC.

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