Description & Overview

Ironweed (Vernonia fasciculata) gets its common name for its tough, rusty green-colored stems among other “iron-like” plant characteristics. This large statured perennial features large clusters of distinctively glabrous bright purple flowers which stand out in the late summer landscape drawing in pollinators from far and wide. It may also be known as Smooth Ironweed because of its smooth leaves and stems.

Core Characteristics

Category: Perennial

Wisconsin Native: Yes

USDA Hardiness Zone: to zone 4

Mature Height: 4-6 feet

Mature Spread: 1-2 feet

Growth Rate: Perennial

Growth Form: Upright

Light Requirements: Full Sun

Site Requirements: Preforms best in moist soils. Drought tolerant.

Flower: Showy. Tight clusters of bright reddish-purple, umbrella-like flowers.

Bloom Period: July to September

Foliage: Dark green

Fall Color: N/A

Urban Approved: Yes

Fruit Notes: Small, tufted seed with coppery brown hairs

Suggested Uses

Ironweed is a very suitable plant to live by a pond, creek, or lake edge. You’ll find it growing naturally in moist to wet soils, although, it grows equally well in average soils. We recommend using it as a backdrop in a low-lying moist location such as a rain garden. It is also a very effective border plant in cottage gardens, prairies, or wildflower meadows. Because it can reach heights of up to 6′, this plant could be used to provide some perennial screening. Ironweed will spread itself readily by seed, so it may not be suitable for smaller settings. Self-seeding can be managed by removing the flower heads before they disperse their seeds. However, the dark, rigid stems when topped with their fluffy, coppery brown seed heads do offer an appealing late-season interest.

Ironweed (Vernonia fasciculata) gets its common name for its tough, rusty green-colored stems among other "iron-like" plant characteristics. This larg…

Wildlife Value

When it comes to Ironweed, there are lots of nectar and pollen rewards for visiting insects. The most common insect attendants are bees and butterflies. There are several notable species of bees you may find around your Ironweed such as solider bees (Chauliognathus spp.), bumble bees (Bombus spp.), and the green sweat bee (Agapostemon spp.).

Several species of butterflies like, monarch, hairstreak, skipper, and swallowtail are also common visitors. There are two species of long-horned bee, Melissodes denticulata and Melissodes vernoniae that are specialists of Ironweed. Specialist bees have specific relationships with only a few plant species. Some specialist bees forage for pollen that can only be found on a single plant species. The benefit to pollinators that Ironweed provides is infallible.

Ironweed is also a larval host plant for the parthenice tiger moth, American lady, and the crossline skipper.

Notably, the foliage of Ironweed is bitter tasting and is generally avoided by mammalian grazers.

Maintenance Tips

Caring for Ironweed starts with proper siting. Thankfully, it’s tough and adaptable which allows it to be grown easily in many locations. Ironweed should be grown in full sun. It’s found growing naturally in wet to moist sites and can tolerate some seasonal flooding. On the other hand, it can also tolerate periods of drought. These two characteristics make it an excellent addition to a rain garden.

One thing to keep in mind is Ironweed tends to spread itself by seed rather aggressively. Generally, Ironweed may be too aggressive for smaller areas unless you provide some competition to help keep it in check. Ironweed’s self-seeding habit can be mitigated by removing the flower heads before they go to seed. This plant can be a good specimen in smaller gardens provided it’s kept in check for seedlings.

This plant is tall growing, reaching heights of up to 6′. This is something that should be kept in mind when siting as you do not want it to overshadow its neighbors. The plant can be kept shorter by cutting the stem in half during late spring to early summer.

Ironweed (Vernonia fasciculata) gets its common name for its tough, rusty green-colored stems among other "iron-like" plant characteristics. This larg…

Pests/Problems

What makes proper siting even easier is that it doesn’t have any major insect or disease problems. Thanks to its bitter-tasting foliage, leaf-feeding insects tend to stay away. You may occasionally find thrips or aphids causing damage if the insect population gets too high, but this scenario is far from common.

Leaf Lore

The genus name Vernonia honors William Vernon, an English botanist who collected seeds in Maryland in 1698 before returning to Cambridge. The specific epithet fasciculata means “in a bundle or cluster.” The common name for Ironweed has been attributed to its “iron-like” qualities such as its tough stems and rusty colored seeds.

Native Americans often used the Ironweed to make healing tea. The leaf tea was most used to treat menstrual pains as well as stomach aches, fever, and toothache. In recent years, the University of Hawaii has been performing studies on Ironweed’s potential to help prevent or treat specific types of cancer. Currently, it’s theorized that an Ironweed extract may prove useful in fighting aggressive types of both breast and brain cancer.

Companion Plants

Because Ironweed is an incredible addition to a rain garden, it pairs well with other rain garden plants such as Joe-Pye Weed, Culver’s Root, Red Milkweed, Big Bluestem, Sedges, and Bee Balm.

This plant makes an excellent candidate to combine with other flower colors, especially yellow or orange. We recommend planting alongside Goldenrod, Butterflyweed, Daylilies, Black-Eyed Susan, Sneezeweed, and Coreopsis.

Ironweed (Vernonia fasciculata) gets its common name for its tough, rusty green-colored stems among other "iron-like" plant characteristics. This larg…
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Written by Miles Minter