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Ironweed
Vernonia
Also called ironwood
Ironweed blooms from August through September.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Ironweed
Plant it in full sun. It prefers moderate water. It is hardy in USDA zones 4–9. Expect it to reach about 5 ft tall and 2 ft wide at maturity, in roughly 2 years (not yet checked).
No toxicity note is on file for Ironweed. That is not a clearance: check its safety for people and pets before planting.
What was checked
Mature height and spread, hardiness zones, sun and the trait tags were checked against named botanical sources for this plant. The bloom months and water need on this page were not, and each fact above says which. The planting, spacing and size sections are derived from these checked facts by a fixed rule, not checked separately, and the plant type is the library's own classification.
When to plant Ironweed
Plant Ironweed in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. In zone 6, the middle of its hardy zones 4 to 9, spring means March to May and fall means August or September. Once settled, it blooms from August to September.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 6, the middle of this plant's hardy range, start with zone 6 in March. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Ironweed get?
5 fttall5 ft 7 inan adult2 ftwideSee Ironweed in a garden plan: the planner shows it in 3D beside everything else you add, growing toward this size over the years.
How far apart to plant Ironweed
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Ironweed about 2 ft apart, center to center, so each plant has room to reach its full width.
Add Ironweed to a garden plan and the planner draws it at its full width, so you see the spacing before you buy.
Where these facts come from
Ironweed's height, spread, hardiness zones, sun and trait tags were checked against 32 published sources on July 31, 2026. Each one is linked below with every fact it carried, which can include a fact this page still marks as not yet checked, because a source carrying a value is not the same as the value being held to the standard. Facts not in that list, and the planting, spacing and size sections, are not covered by these sources.
- NC State ExtensionVernonia noveboracensisheight, spread, hardiness zones, sun, years to mature size and trait tags
- NC State ExtensionVernonia lettermanniiheight, spread, hardiness zones, sun, years to mature size and trait tags
- NC State ExtensionVernonia angustifoliaheight, spread, hardiness zones, sun, years to mature size and trait tags
- NC State ExtensionVernonia glaucaheight, spread, hardiness zones, sun, years to mature size and trait tags
- NC State ExtensionVernonia lettermannii 'Iron Butterfly'height, spread, hardiness zones, sun, years to mature size and trait tags
- Perennials.com (Heritage Perennials)Heritage Perennials (Vernonia noveboracensis)height, spread, hardiness zones, sun, years to mature size and trait tags
- Missouri Botanical GardenVernonia arkansanaheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenVernonia baldwiniiheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenVernonia fasciculataheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenVernonia giganteaheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenVernonia lettermaniiheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenVernonia lettermanii 'Iron Butterfly'height, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenVernonia missuricaheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenVernonia 'Prairie Princess'height, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenVernonia 'Southern Cross'height, spread, hardiness zones, sun and trait tags
- NC State ExtensionVernonia giganteaheight, spread, hardiness zones, sun and trait tags
- Prairie Moon NurseryVernonia missuricaheight, hardiness zones, sun, years to mature size and trait tags
- University of Arkansas ExtensionUniversity of Arkansas Cooperative Extension Service, Plant of the Wee...height, spread, hardiness zones, sun and trait tags
- Clemson Home and Garden Information CenterClemson Cooperative Extension Home & Garden Information Center, Ironweedheight, spread, sun and trait tags
- Missouri Botanical GardenVernonia noveboracensisheight, spread, hardiness zones and sun
- Prairie Moon NurseryVernonia fasciculataheight, hardiness zones, sun and trait tags
- Prairie Moon NurseryVernonia giganteaheight, hardiness zones, sun and trait tags
- prairienursery.comPrairie Nursery (Vernonia fasciculata)height, hardiness zones, sun and trait tags
- University of Illinois ExtensionVernonia fasciculataheight, hardiness zones, sun and trait tags
- Lady Bird Johnson Wildflower CenterVernonia noveboracensisheight, sun and trait tags
- Lady Bird Johnson Wildflower CenterVernonia giganteaheight, sun and trait tags
- University of Maryland ExtensionHome & Garden Information Center, New York Ironweedheight, sun and trait tags
- Missouri Department of ConservationVernonia spp.height and trait tags
- Missouri Department of ConservationField Guide, Missouri Ironweedheight and trait tags
- Lady Bird Johnson Wildflower CenterVernonia lettermanniiheight
- Mt. Cuba CenterVernonia trial reporttrait tags
- toadshade.comToadshade Wildflower Farm (Vernonia noveboracensis)trait tags
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Ironweed
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note. A note reports what its source says; where that differs from a fact above, the fact above is this entry's stored value, and its mark says whether it has been checked.
Worth knowing
In the daisy family, yet its flower heads have only tiny disc florets and no petal-like ray florets, so they read as fluffy tufts, not daisies. per NC State
Watering splits by species
The wet-meadow types (New York, western/prairie ironweed) want steady moisture and suit rain gardens; upland Appalachian and Letterman's ironweed prefer average to dry soil. Match yours to the site. per NC State
Deer resistant, one exception
Bitter foliage makes New York, giant and Letterman's ironweed reliably deer resistant. The exception is Appalachian ironweed (V. glauca), which deer are drawn to: avoid it in deer country. per NC State
Size varies by species
The slug covers several Vernonia species: from compact Letterman's ironweed at 2 to 3.5 ft up to New York (5 to 8 ft) and giant ironweed near 12 ft. per NC State
Cut tall types back
The tall types lean and flop. A late-spring Chelsea chop, cutting them back by a third to a half before flower buds set, keeps them shorter and upright. per NC State
Late-season pollinator magnet
It blooms in late summer and fall when little else flowers, feeding butterflies, monarchs, bees and other pollinators through the pre-winter and migration window. Songbirds later eat the seeds. per NC State
Leave winter stems standing
The hollow dead stems shelter stem-nesting bees, so leave them standing about 12 to 24 in over winter before cutting down, rather than a hard fall cleanup. per NC State
What pairs well with Ironweed
Good companions share its growing conditions and add something it lacks: an earlier or later bloom, a lower carpet in front, or structure through winter.
White Clover
Shares full sun and moderate water; blooms in late spring, before this one opens; low at 4 in, to carpet the ground beneath; both are strong pollinator plants, and they feed in different months.
Thyme
Shares full sun and low to moderate water; blooms in late spring, before this one opens; low at 6 in, to carpet the ground beneath; both are strong pollinator plants, and they feed in different months.
Japanese Stewartia
Takes full sun to part sun and moderate water; blooms in early summer, before this one opens; both are strong pollinator plants, and they feed in different months; taller at 16 ft, for the layer behind it.
Creeping Phlox
Shares full sun and low to moderate water; blooms in mid spring, before this one opens; low at 6 in, to carpet the ground beneath; both are strong pollinator plants, and they feed in different months.
Hyacinth
Shares full sun and moderate water; blooms in early spring, before this one opens; lower at 10 in, for the front of the border; both offer pollinator forage, in different months.
Chives
Shares full sun and moderate water; blooms in late spring, before this one opens; both are strong pollinator plants, and they feed in different months; lower at 12 in, for the front of the border.
Sweet Alyssum
Shares full sun and moderate water; overlaps, then carries the display into mid fall; low at 5 in, to carpet the ground beneath; both are strong pollinator plants.
English Daisy
Shares full sun and moderate water; blooms in mid spring, before this one opens; low at 6 in, to carpet the ground beneath; both offer pollinator forage, in different months.
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