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Species Spotlight: Tall Ironweed (Vernonia gigantea)

Updated: Dec 11, 2022

tubular flowers of Giant Ironweed

Interesting facts:

  • The genus name, Vernonia, is in honor of an English botanist, William Vernon

  • Overall, Tall Ironweed is a somewhat unexceptional native ornamental but flowers during the hottest, driest days of summer.

Native Environment/Plant Information:

Tall Ironweed has a tall, narrow growth habit, usually growing 3 to 5 feet tall but occasionally growing up to 12 feet tall. Tall Ironweed generally has a clumping habit. Tall Ironweed has a root system consisting of short, thick rhizomes and fibrous roots. The base sends up one or more stiff, upright stems that range from green to red to purple in color. The stems do not generally branch except near the top at the flower heads. Leaves can be up to 10” long and are dark green on the upper surface and lighter on the lower surface. The stem terminates in a flat-headed panicle of flower heads. The panicle can measure 12-16 inches across and contains numerous composite flowers (Aster Family). Each composite flower is comprised of 10-30 tubular disk flowers. Tall Ironweed lacks the conspicuous, showy ray flowers that many Aster Family plants, such as sunflowers and asters, have. The flower color can range from magenta to lavender to deep purple and generally appear in July and August in this area. Pollinated flowers develop rusty-colored seed clusters consisting of tiny achenes with tufts of bristles that are easily dispersed by the wind.

Tall Ironweed is highly adaptable to different soil and moisture conditions, but it does prefer full sun. Tall Ironweed is tolerant of drought conditions, and it is tolerant of periodic flooding. It grows tallest in rich soils with consistent soil moisture. Tall Ironweed is most commonly found in open, upland sites such as old fields, prairies, grasslands, meadows, savannas, open woods, woodland edges, roadsides, floodplains, and even near stream banks. The plant is commonly found in overgrazed pastures; livestock avoid this plant resulting in the germination of the many seeds.

Tall Ironweed tends to hybridize with some other native Ironweeds, which can sometimes complicate plant identification.

Cultural Information:

Tall Ironweed is easiest to grow average, moist soils, performing quite well in average garden soils. It will flower best in full sun but is adaptable to some shade. Tall Ironweed grows well in a mixture of loam, clay-loam, or sandy-loam soils. It is tolerant of heat, of humidity, of poor soil, and of drought once established.

Tall Ironweed has low fertility needs; low fertility also helps limit how tall it will grow. Another way to manage the height of Tall Ironweed is to mow it or cut it back in mid-Spring (April or May). Tall Ironweed can freely self-seed given the right conditions, and the plant should be deadheaded if reseeding is not desired. Deadheading can also prolong the blooming. Tall Ironweed clumps can be divided when dormant. It will compete with other plants in the garden and can become weedy if not controlled.

Tall Ironweed works best for naturalizing in cottage gardens, wildflower meadows/gardens, prairies, and native plant gardens. It also works well in butterfly gardens, pollinator gardens and borders. Due to its height, it is best planted in the back of a border garden.

Native Americans made a “blood tonic” for bleeding and stomachaches <6>.

Wildlife uses:

Tall Ironweed are very attractive to butterflies, skippers, and bees (primarily long-tongued bees). Vernonia are host plants for caterpillars of various moths feed, particularly the pith of their stems and their roots. These species include Eupatorium Borer Moth (Carmenta bassiformis), Ironweed Borer Moth (Papaipema cerussata and Papaipema limpida, Red Groundling (Perigea xanthioides), Pyralid Moth (Polygrammodes flavidalis and Polygrammodes langdonalis). The Ironweed Aphid (Aphis vernoniae) is known to sucks juices from the upper stems and leaf undersides. Other insects feeders include the larvae of Ironweed Bud Midge (Asphondylia vernoniae) and Ironweed Blossum Midge (Youngomyia podophyllae). The Four-Spotted Tree Cricket (Oecanthus quadripunctatus) and Short-winged Meadow Katydid (Conocephalus brevipennis) are known to feed on the flowerheads.

Because of the bitter foliage, mammalian herbivores and livestock avoid Ironweed species as a food source. As a result, these plants can become more abundant in pastures over time.

Two pollinators on Giant Ironweed

Useful Links and References:

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