How to Plant & Grow New York Ironweed (Vernonia noveboracensis)


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Ironweed in bloom
A single ironweed flowerhead can contain up to 50 tiny purple flowers! Famartin, CC BY-SA 4.0, via Wikimedia Commons

Perfect for cottage gardens and native meadows, Vernonia noveboracensis is an herbaceous perennial. It is commonly known as tall ironweed, New York ironweed, or vein-leaf hawkweed. 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.

V. 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.

Facts, Benefits & Uses of New York Ironweed

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.

Ironweed, along with its close cousins, is highly attractive to butterflies, bees, and many other nectar-loving insects. The longhorn bee (Melissodes denticulatus) has a well-established relationship with ironweed and is one of its most effective pollinators. Songbirds benefit from the plant’s seed clusters, which appear in late fall to winter.

Due to its attractive features and low-maintenance requirements, the North Carolina Botanical Garden selected ironweed as the Wildflower of the Year in 2004. It is a highly adaptable species that can thrive in a wide variety of landscape types. Despite its moderate edibility and potential as a browsing plant for livestock, it is also fairly resistant to grazing by deer.

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New York Ironweed Fact Sheet:
PLANT TYPE
Herbaceous perennial
HARDINESS ZONES
USDA 5 – 9
LIGHT REQUIREMENTS
Full sun to partial shade
BLOOM COLOR
Deep lavender to red-violet
BLOOM PERIOD
July to September
MAXIMUM GROWTH
8 feet
PLANTING DEPTH
Soil surface (for seeds), 2 – 3 inches (for cuttings)
WATER QUALITY
Slightly acidic (pH 5.8 – 6.5)

New York Ironweed Growth, Hardiness & Climate

Ironweed plant in a field
Ironweed can become naturalized in meadows and pastures with water access. Doug McGrady / CC BY 2.0

Ironweed tends to have shallow root systems with a maximum depth of just 6 inches (15 cm). Considering its tolerance for various conditions, its dispersal and coverage are surprisingly limited. This is due to its inability to self-propagate vegetatively. Also, it produces small seed sets that may thoroughly be consumed when large bird populations are present.

Populations of this species often occur along coastlines, where the soil is kept moist throughout the year. They favour 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.


How to Plant New York Ironweed

Ironweed stems & flowers
Late spring is the best time to collect softwood cuttings and should be about 5 – 6 inches long. Fritz Flohr Reynolds / CC BY-SA 2.0

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.

V. 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.


How to Care for New York Ironweed

Ironweed buds
Ironweed is a late bloomer and may not flower until the second year of cultivation. rockerBOO / CC BY-SA 2.0

Low-maintenance and eager to produce new stems each year, the resilient ironweed deserves a permanent spot in every wildflower garden. It can be pruned back or cut down without much consequence to the plant’s growth or survival. It is generally pest and disease-resistant but does have a mutualistic relationship with two honey-producing insects (Aphis vernoniae and Publilia reticulata), which are tended to by ants. These ant-aphid associations protect ironweed by repelling potential grazers and parasites.

Flowering may not occur until the second year of cultivation, so don’t be too concerned if your new plant is a late bloomer. Ironweed stands can be expected to spread slowly on their own as they self-seed. If you wish to prevent self-seeding and prolong the bloom period, flowers can be deadheaded as soon as they are spent. Cutting down shoots to the ground in early spring can also help with overall height management. Lastly, make sure to keep the soil moist throughout growth periods. The addition of organic compost or mulch can help prevent moisture loss and provide additional nutrients.


How to Winter New York Ironweed

Ironweed is able to survive outdoors through cold months, during which its leftover rust-coloured seed heads provide winter interest. As it is hardy to USDA hardiness zones 5 – 9, it can withstand temperatures that drop to -28˚C (-18˚F). The plant may lose its leaves, but its shoots should stay intact as the roots enter dormancy. Its common name actually refers to the toughness of its stems, so you need not worry about leaving your ironweed plants outdoors.


Is New York Ironweed Invasive or Toxic?

Wild ironweed varieties may grow more aggressively compared to store-bought (domesticated) ones. It would be best to avoid propagating this species from wild-sourced cuttings and seeds. V. noveboracensis is not considered invasive, though it would be prudent to keep in mind that this species self-sows. It is a frequent recommendation for gardeners looking to substitute invasive plants with native wildflowers.

Ironweed is not considered a toxic plant, but it can cause allergies. Skin irritation is a common reaction from contact with the plant, especially for those who regularly have compositae allergies. Reactions are seldom severe, however, and should simply die down shortly after contact.


Is New York Ironweed Edible? Will Animals Eat it?

Ironweed is not widely regarded as edible due to its bitter-tasting foliage. Its roots do have medicinal potential and were once used to create blood tonics for regulating menstruation and childbirth pain. Native Americans made ironweed root infusions that could supposedly treat everything from stomach ulcers to lose teeth! Like most alternative treatments, this natural remedy has not been FDA-approved and must be used cautiously.

Livestock may feed on ironweed in the absence of other herbaceous edible plants. Wild animals tend to avoid feeding on its foliage and shoots, likely due to their bitter taste. Consider adding this species to your roster of native plants if your garden is often visited by grazers.


Where to Buy New York Ironweed & Seeds? (UK & US)

As Vernonia noveboracensis is a frequent favourite, it should be available in plant nurseries or landscaping stores throughout its native range. If you are located elsewhere, you may have more luck obtaining seeds or plug plants from online plant portals. Avoid taking this species from the wild, even if it is widespread in your area, and make sure it is sourced from a reputable nursery.

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