How to Grow and Care for New York Ironweed

New York ironweed

The Spruce / Letícia Almeida

New York ironweed (Vernonia noveborecensis) is a towering upright perennial wildflower native to the eastern and southeastern U.S., where it is commonly found in wet meadows and pastures, streambanks, low-lying woods, and marshes. Its sturdy stems are covered with long, lance-shaped leaves, and fluffy deep purple composite flowers, 3 to 4 inches wide, cluster at the top of the plant from late summer into early fall.

Along with other species in the Vernonia genus, New York ironwood holds appeal to gardeners who prefer native plants. Growing up to 7 feet tall, this member of the aster family is popular in wildflower gardens, where during the growing season butterflies, bees, and other pollinators flock to it for its nectar. Out of season, the New York ironweed's tall, dead stalks provide sturdy perches for migrant birds. New York ironweed is a fast-growing, fast-spreading plant that is normally planted in the spring from potted nursery starts or in the fall from direct-sown seeds. Even when grown from seeds, it sometimes blooms in its first summer season.

Common Name New York Ironweed, ironweed
Botanical Name Vernonia noveboracensis
Family Asteraceae
Plant Type Herbaceous perennial
Mature Size 4–7 ft. tall, 3–4 ft. wide
Sun Exposure Full
Soil Type  Rich, moist
Soil pH Acidic (5.0 to 6.5); tolerates neutral soil
Bloom Time Late July to September
Flower Color Purple
Hardiness Zones 5–9 (USDA)
Native Area Eastern and Southeastern North America
New York ironweed in a garden
The Spruce / Letícia Almeida 
closeup of New York ironweed
The Spruce / Letícia Almeida 
New York ironweed cluster
The Spruce / Letícia Almeida 
closeup of New York ironweed
The Spruce / Letícia Almeida 
A close-up of New York Ironweed.
opus1ny/iStock/Getty Images 

New York Ironweed Care

Like many native wildflowers, ironweed is quite easy to grow. It prefers rich, moist soil that is slightly acidic, but it will readily survive in less favorable conditions. These are large plants, so space them at least 24 inches apart—they will quickly fill in. Be aware that there are several Vernonia species that are sold as ironweed, so pay attention to the botanical name when purchasing. All ironweeds have similar care needs, but the size and growth patterns can be quite different. New York ironweed suffers from no serious pest or disease issues.

New York ironweed is such a dramatic plant that you might be tempted to dig up and adopt wild plants you find on public lands or along roadsides to transplant into your own garden. But if this plant is growing wild in your region, it's possible that you will find it to be overly aggressive in your garden. And in some regions, it may be illegal to remove and replant any wild plant species.

Warning

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.

Light

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.

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.

Water

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.

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.

Types of Ironweed

In addition to New York ironweed, there are several other species in the Vernonia genus, and some of them are even more popular than New York ironweed as garden plants, especially for colder climates. Some other ironweed species you should consider:

  • Vernonia gigantea  'Jonesburo Giant' grows to as much as 12 feet tall and 5 feet wide. Deep purple flower clusters appear in autumn. It is hardy in zones 5 to 8.
  • V. angustifolia 'Plum Peachy' is a 42-inch-tall blue-violet variety that is hardy in zones 7 to 9.
  • Vernonia lettermannii or "Iron Butterfly" has deep purple flowers on short, 3-foot-tall plants. This summer bloomer is hardy in zones 4 to 9.
  • Vernonia or "Summer’s Surrender" is a hybrid cross of V. lettermannii and V. arkansana. It has violet flowers on 4-foot plants and is hardy in zones 4 to 9.
  • Vernonia or "Summer’s Swan Song" is a hybrid created by crossing V. lettermannii and V. angustifolia "Plum Peachy." It has violet flowers on 3- to 4-foot plants and is hardy in zones 4 to 9.

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 invasively. At the end of the growing season, garden plants can be cut down to near ground level.

Propagating New York Ironweed

New York ironweed should be divided every three to four years to keep the plant healthy and to create new plants to share. Here's how to do it:

  1. In fall or early spring, dig up the root clump with a shovel.
  2. Carefully cut away dead parts of the crown and roots with a sharp knife.
  3. Cut the leftover crowns and roots into pieces for replanting.
  4. Replant the pieces in the desired garden location, leaving 12 to 24 inches of space between pieces.

How to Grow New York Ironweed From Seed

New York ironweed is fairly easy to grow from seeds, either by direct sowing in the garden or starting seeds indoors.

For outdoor direct-seeding, plant the seeds in the desired location, about 1/8 inch deep. Leave them to overwinter, and the seeds will germinate and sprout in the spring.

If starting seeds indoors, they will need a period of cold stratification. Plant them 1/8 inch deep in flats or pots filled with commercial potting mix, cover them with plastic, and refrigerate for about three months. At this time, take the pots out and uncover them, then place them in a warm, bright location until the seeds sprout. When the seedlings are at least 2 inches tall, they can be transplanted into the garden after a hardening off period.

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.

Common Pests and Plant Diseases

As befits a wildflower that is sometimes criticized for invasiveness, New York ironweed has no serious pest or disease issues.

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.

How to Get New York Ironweed to Bloom

This plant rarely withholds its flowers, which generally appear from midsummer well into fall. 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.

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.

Common Problems With New York Ironweed

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 invasiveness, 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.

FAQ
  • How do I use New York ironweed in a landscape?

    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.

  • Why "iron"? Why "New York"?

    The name "ironweed" may derive from the sturdy, thick stems of the plant; or from the rusty color of the seeds and fading flower heads. It is called "New York" ironweed because New York state was where the plant was first collected.

  • How long does ironweed live?

    You can keep ironweed growing almost indefinitely if you lift, divide, and replant the root clump every few years. Without this attention, the plant usually still lives on, though may grow woody and sparse in the center as the plant gradually spreads outward.

  • What is the difference between New York ironweed and Joe-Pye weed?

    New York ironweed and Joe-Pye weed (Eutrochium spp.) are often confused for one another because both aster-family wildflowers like the same environments and have similar appearances. But Joe-Pye weed is usually a shorter plant with leaves that oppose on the stems, while ironweed has leaves that are alternately arranged. Joe-Pye weed has flowers that are less tightly formed, while New York ironweed has flowers that are decidedly aster-like.