Vernonia gigantea - Ironweed
Vernonia gigantea - Ironweed
Vernonia gigantea - Ironweed
Vernonia gigantea - Ironweed
Vernonia gigantea - Ironweed
Vernonia gigantea
Ironweed
I planted 4 young plants of this huge perennial in full sun, in rich, well-worked soil. I’ll let you know next summer how they’ve done. They are accompanied by the Arkansanna variety of the same species and by tall grasses.
yann, 31/08/2025
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Description
Vernonia gigantea is the tallest and most impressive of the Vernonia genus which includes robust perennials closely related to large asters. This magnificent wild vernonia has brilliantly coloured, eye-catching violet-purple flowers in the second half of summer. This proud plant is formed by tall sturdy stems adorned with large leaves, particularly ornamental in rich and moist soil. It thrives in the sun, in the back of a border with large asters, or near water.
Vernonia gigantea belongs to the Asteraceae family. It is a perennial herbaceous plant native to the eastern United States where it can be found in wet ditches along roads, in meadows, and open forests. Anchored by a strong perennial crown, this species can reach heights between 2 and 3 metres (7 and 10 feet), and spread 70-80 cm (28-32in) on the ground. The size of the plant depends on the fertility of the soil and its moisture content. Its growth is quite fast, but it takes two years to establish. It forms a clump of tall and sturdy, straight, more or less hairy stems ranging from green to purple, bearing large alternate, simple, ovate, dark green leaves up to 23 cm (9in) long. Flowering occurs from August to September-October depending on the climate. At the tips of the stems, small fluffy, violet to magenta-purple pompom flowers appear, gathered in terminal bunches or corymbs. The flowers all open at the same time and are covered in butterflies. The vegetation is deciduous: it emerges from the ground each spring and dies in autumn.
Vernonia gigantea is easy to grow in the sun in consistent, slightly moist soil and blends well with a multitude of plants to form magnificent autumn compositions, especially with large asters and Meadowsweets; on the banks of a pond, it spreads quickly and looks good with joe-pye weeds, Lythrum salicaria, Filipendula rubra 'Venusta', Euphorbia palustris. In a wilder style, in the back of a border, this imposing perennial forms a very successful combination with Rudbeckia maxima, Red Angelica, and tall grasses: Miscanthus 'Malepartus', Panicum, Stipa...
Vernonia gigantea - Ironweed in pictures
Flowering
Foliage
Plant habit
Botanical data
Vernonia
gigantea
Asteraceae
Ironweed
North America
Planting and care
Vernonia gigantea is a robust and hardy perennial plant that should be better known. It thrives in sunny positions in rich and deep soil, and tolerates clay soils well. It does not tolerate drought, but grows in any damp or moist soil. In very compact and heavy soil, leaf compost and coarse sand should be incorporated when planting. The clumps can be divided in spring or autumn when they become too large. Cutting back the vegetation in late spring helps to limit the height of the plant. Prune after flowering if you want to avoid self-seeding, or in late winter.
Planting period
Intended location
Care
Planting & care advice
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Hardiness is the lowest winter temperature a plant can endure without suffering serious damage or even dying. However, hardiness is affected by location (a sheltered area, such as a patio), protection (winter cover) and soil type (hardiness is improved by well-drained soil).
In temperate climates, pruning of spring-flowering shrubs (forsythia, spireas, etc.) should be done just after flowering.
Pruning of summer-flowering shrubs (Indian Lilac, Perovskia, etc.) can be done in winter or spring.
In cold regions as well as with frost-sensitive plants, avoid pruning too early when severe frosts may still occur.
The harvesting period indicated on our website applies to countries and regions in USDA zone 8 (France, England, Ireland, the Netherlands).
In colder areas (Scandinavia, Poland, Austria...) fruit and vegetable harvests are likely to be delayed by 3-4 weeks.
In warmer areas (Italy, Spain, Greece, etc.), harvesting will probably take place earlier, depending on weather conditions.
The sowing periods indicated on our website apply to countries and regions within USDA Zone 8 (France, UK, Ireland, Netherlands).
In colder areas (Scandinavia, Poland, Austria...), delay any outdoor sowing by 3-4 weeks, or sow under glass.
In warmer climes (Italy, Spain, Greece, etc.), bring outdoor sowing forward by a few weeks.
The planting period indicated on our website applies to regions in USDA Zone 9a (East Coast and Midlands: Dublin, Wexford, Waterford, Kilkenny, Portlaoise). It will vary depending on where you live:
- On the west coast and in the north-west (Galway, Limerick, Sligo, Donegal, Westport), delay planting by 1 to 2 weeks in spring and bring it forward by 1 to 2 weeks in autumn compared to the dates given, preferably choosing periods without strong winds.
- In the inland hills and plateaus (Wicklow Mountains, Macgillycuddy’s Reeks, Connemara, Killarney), it is best to plant in spring (April–May) or autumn (September–October), avoiding periods of waterlogged soil in winter and strong winds, which pose the main risk to newly planted trees in these areas.
The flowering period indicated on our website applies to regions in USDA Zone 9a, such as the East Coast and Midlands, including Dublin, Wexford, Waterford, Kilkenny and Portlaoise.
This will vary depending on where you live:
- On the west coast and in the northwest (Galway, Limerick, Sligo, Donegal and Westport), it will be delayed by one to two weeks compared to the given dates, due to stronger Atlantic winds and less spring sunshine.
- In the inland hills and plateaus (the Wicklow Mountains, the Macgillycuddy's Reeks, Connemara and Killarney), flowering will be delayed by two to three weeks. Flowering mainly occurs between May and July, with the limiting factors being less frost and more of the excessive humidity, strong winds and lack of sunshine that are characteristic of these areas.
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