Giant Ironweed

Description

Vernonia gigantea, also known as Giant Ironweed or Tall Ironweed, is one of five native ironweeds in Missouri. It is a perennial forb (wildflower) that can grow to be up to 10 feet tall! Like other ironweeds, it is an upright plant. It bears branching, rounded clusters of fuzzy-looking magenta or purple flowerheads in mid to late summer.

The large, intense purple flowers attract a wide array of bees, beetles, flies, butterflies, skippers, and other insects. These may feed on pollen, nectar, or both.

At least two species of digger bees and the eastern ironweed long-horned bee are specialized to collect pollen primarily, or perhaps only, from ironweed species.

Many other kinds of insects eat the leaves or flowers or bore into the stems or roots or suck the sap. These include midge, moth, and beetle larvae, aphids, stink bugs, grasshoppers, tree crickets, and katydids. Some species of moths use ironweeds as their caterpillar food plants. Leaf miners are insects whose larvae tunnel around within the leaves. They eat the fleshy green tissues between upper and lower surfaces.

Crab spiders, orbweavers, assassin bugs, robber flies, and other predatory arthropods hunt the many insects that visit the flowers or feed on the plants.

Though a colony of ironweeds can be the home of nearly an entire food chain’s worth of insects and other small animals, mammals typically don’t eat the bitter plants.

In the Midwest, ironweeds are a familiar sight in overgrazed pastures, apparently because the plants are unpalatable to cattle. Most species in this genus produce toxic chemical compounds. However, the species that occur in Missouri have not yet been implicated directly in livestock or human poisoning.

Ironweeds can be good choices for native wildflower gardening. They provide vibrant late-season color, especially when paired with bright yellow goldenrod, which blooms about the same time. Easily grown in average, medium to wet soils in full sun to part shade. Although it is often seen growing in the wild in moist soils, with tolerance for periodic flooding, it performs quite well in cultivation in average garden soils. Plants generally grow taller in moist soils. Overall plant height may be reduced by cutting back stems in late spring. Easily grown from seed. Remove flower heads before seed develops to avoid any unwanted self-seeding. Naturalize in cottage gardens, wildflower meadows, prairies or native plant gardens. Also effective as a background plant for borders. Good for areas with moist soils.

Occurs on banks of streams, rivers, spring branches, margins of ponds and lakes, bottomland forests, swamps, bottomland prairies, fens; also pastures, ditches, and roadsides. This species of ironweed tends to hybridize with some other native ironweeds, which can sometimes complicate plant identification.

Videos About Native Plants

To learn more about native plants that bloom at the same time, check out this video.