Ironweed (Vernonia noveboracensis)

Ironweed, New York Ironweed, Tall Ironweed

The ironweed, a wildflower with the potential to become an invasive weed in the eastern United States, is grown as a decorative plant in various types of gardens. This is a tall, clumping shrub that draws butterflies, bees, and other pollinators. Parts of this plant are known to be used as herbal medicine by the Cherokee.

I. Appearance and Characteristics 

Vernonia noveboracensis, the New York ironweed or vein-leaf hawkweed, is a plant in the family Asteraceae. It is native to the eastern United States, from Florida to Massachusetts and west to Tennessee, Alabama, and West Virginia and to southern Ontario.

This clump-forming species is classified under the large Asteraceae family, which includes 1,900 genera of flowering plants! Vernonia is but a small group of bitter leaf plants under this family, with species that tend to hybridize with one another due to their overlapping distributions. More than a handful occur in North America, with V. noveboracensis having a native range restricted to the eastern United States.

Ironweed is set apart by its tall stems, which can bear flowers on shoot tips as far as 8 feet (2.4 meters) off the ground! Its disk-shaped floral heads occur as dense clusters. In summer to early fall, a single floral head can be composed of up to 50 tiny purple flowers. These look like fluff and are quite vivid in color, complementing the plant’s narrow, deep green leaves. When pollinated, the flowers develop into rust-colored seed clusters. A single ironweed can spread to 2 – 4 feet (61 – 122 cm) wide if given ample space, making it an ideal border plant.

noveboracensis is often likened to or mistaken for Joe Pye weed (Eutrochium spp.) because they tend to grow in the same environments and have similar morphologies. The latter is usually shorter and has opposing pairs of foliage, whereas ironweed has alternately arranged leaves.

As this species favors moist soil, it is ideal for pond edge placement. Its leafy shoots can bring many decorative and ecological benefits. Novice gardeners need not be intimidated by this tall plant. The stems can be cut at different heights to create dimension and to spread out blooms. Near-bottom blooms are a great way to manage pollinator distribution, encouraging them to veer closer to the pond’s surface.

Populations of this species often occur along coastlines, where the soil is kept moist throughout the year. They favor low-lying wetland regions and may also become naturalized in roadsides, meadows, and pastures with water access. Remarkably, healthy ironweed stands are able to withstand brief drought periods as long as other ambient conditions are optimal. Hardy to USDA zones 5 – 9, it thrives best in mild temperatures. Slightly acidic, fertile soils are ideal for cultivation.

New York ironwood can be aggressive to the point of invasiveness when planted in areas with perpetually moist soil. Be on alert for the plant spreading outside its boundaries into nearby wetland areas. Other members of the Vernonia genus, especially the hybrids, may be better choices if rampant spread is a concern.

II. How to Grow and Care

Sunlight

New York ironweed plants prefer full sun, but can thrive in partial sun, too. This plant needs at least four hours of direct sunlight each day, but six to eight hours is better. If you live in a colder climate, the plant will prefer as much sun as possible.

Temperature and Humidity

New York ironweed readily tolerates the heat and humidity patterns throughout its hardiness range, zones 5 to 9. Where the climate is naturally arid, it may require more ground watering.

Watering

Because ironweed prefers moist soil, it will need at least 1 inch of water per week, and will readily tolerate even more. It will also do quite well in boggy, poorly draining soils where many other plants struggle.

Soil

Ironweeds are hardy plants, so they can adapt to many different kinds of soil, though they will naturally thrive in moist, loamy soil that is somewhat acidic in pH. Extremely barren, dry soil is the only environment where this plant is likely to perish.

Fertilizing

New York ironweed does just fine without supplemental fertilizing during the growing season. If you want to give it a boost, add a top-dressing of compost in the spring.

Pruning

New York ironweed requires no pruning, but deadheading spent flowers is a good idea if you want to limit its self-seeding habit, which can cause the plant to spread aggressively. At the end of the growing season, garden plants can be cut down to near ground level.

Propagation

Ironweed can be propagated via seed. Softwood cuttings and divisions may also successfully generate new tissues, though they are seldom used in regular cultivation. Collect seeds approximately 3 – 4 weeks after the bloom period. For best results, aim to plant them when they are fresh. Seeds can be sown either indoors, in a dedicated germination setup, or outdoors in late fall.

  1. noveboracensis seeds usually have low germination rates, so they must be sown generously. If sowing seeds in their permanent outdoor placements, make sure to sow thickly and thoroughly on topsoil. Lightly press the seeds into the substrate. If growing indoors, you can either sow the seeds before cold stratifying them, or vice versa. Mixing the seeds into a moist, sandy substrate and then storing them in a refrigerator for at least 2 months should increase germination rates. These can then be transferred to a consistently moist substrate.

Late spring is the best time to collect and propagate softwood cuttings. Cuttings that are about 5 – 6 inches (12 – 15 cm) long should suffice. Remove bottom leaves prior to dipping the ends of each stem into the rooting hormone. These can then be planted in 2 – 3 inches (5 – 8 cm) of sterilized soil. 

Potting and Repotting

Perennial wildflowers such as New York ironweed are not commonly grown in container culture, but should you want to try it, any well-draining container filled with a general-purpose potting mix will work. Potted plants will need more frequent watering. Remember that perennials grown in containers may need some shelter in the winter, as the roots are more exposed to cold than they are when growing in the ground.

Overwintering

These hardy plants need no special winter protection. Some gardeners like to cut off the dead stalks to just above ground level as winter sets in, but others like to leave the stalks and dried flower head intact to serve as resting/feeding perches for winter birds.

Pests and Diseases

New York ironweed does not elicit many complaints from gardeners who appreciate native plants and wildflowers. You may observe a couple of issues, however:

Plant Is Spreading Too Rapidly

A New York ironweed plant that spreads quickly, to the point of aggressiveness, is announcing that it very much likes the conditions in which you’ve planted it. This can often occur where ironweed is growing in boggy areas that are constantly moist. You may need to remove the plant entirely if this behavior is a problem or be prepared to dig out the expanding roots frequently.

Plants Are Unusually Short

If your New York ironweed plant is considerably shorter than the 7-plus feet that is normally expected, it is probably because it is soil that is too dry. Increasing the watering volume and intervals may prompt taller growth.

It’s also possible you have mistakenly planted another of the species in the Vernonia genus. There are other native species of ironweed that grow only to 3 or 4 feet in height.

III. How to Get to Bloom

It’s not uncommon for newly planted specimens to bloom weakly, or not at all, in their first year, especially if soil conditions are less than ideal. Be patient; by the second year, they should bloom vigorously.

Bloom Months

This plant rarely withholds its flowers, which generally appear from midsummer well into fall, from the months of July through September.

What Do New York Ironweed Flowers Look and Smell Like?

New York ironweed’s sturdy stems are covered with long, lance-shaped leaves and fluffy deep purple composite flowers, 3 to 4 inches wide, that cluster at the top of the plant from late summer into early fall. Although the flowers are not fragrant, their nectar attracts pollinators.

How to Encourage More Blooms

If a plant does not bloom, it’s possible that it is not getting enough sun. If a clump begins to bloom less vigorously, it may be a sign that the plant needs to be dug up, divided, and replanted in order to rejuvenate it.

IV. Uses and Benefits 

Due to its larger size, the New York ironweed is best-suited for large gardens, butterfly gardens, meadows, wildflower gardens, prairies, or the back of perennial borders. On an even larger scale, New York ironweed can protect mass plantings from soil erosion.

Ironweed looks especially natural and complementary when planted with other fall composite flowers, such as Joe Pye weed, goldenrod, or bright yellow sunflower species. 

If you’re concerned with deer damaging your garden, ironweed plants make an excellent choice because they are rarely browsed.

Ironweed (Vernonia noveboracensis) Details

Common name Ironweed, New York Ironweed, Tall Ironweed
Botanical name Vernonia noveboracensis
Plant type Herbaceous Perennial
Hardiness zone 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
Growth rate Medium
Harvest time Fall
Height 5 ft. 0 in. - 8 ft. 0 in.
Width 5 ft. 0 in. - 8 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Purple/Lavender
Leaf color Green