Ironweed 'Iron Butterfly'
Vernonia lettermannii 'Iron Butterfly' · Asteraceae
A rounded mound of thread-fine leaves, like a bluestar, covered with small, vivid purple flowers in early autumn. It tolerates both drought and brief flooding.
- Size
- 2½ ft tall, 2½ ft wide
- Zones
- 4 to 9
- Light
- Full sun
- Flowers
- Late August to early October
- Pets
- No toxicity recorded
- Job in a bed
- Drift
A bed built around ironweed 'Iron Butterfly'
The planner designed this bed around ironweed 'Iron Butterfly' when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, full sun. It chose the other plants from the 715 that suit those conditions and its dry soil, and says below why ironweed 'Iron Butterfly' stands where it does.
The plants
- 1 Ironweed 'Iron Butterfly' × 3, purple
- 2 Bloody cranesbill 'Max Frei' × 5, pink
- 3 Winter heath × 5, white
- 4 New England aster 'Alma Pötschke' × 4, pink
- 5 Silver sage × 1, silver leaves
- 6 Star of Persia × 4, purple
- 7 Schubert's allium × 3, pink
Why this plant
- The only dense clusters. The others are open bowls, bells, daisies and others. Shape reads at a distance, where colours blur.
Why here
- Anchors a back corner. At 2½ ft it is one of the taller plants here, and the tallest close the ends of the bed, where they stand in front of nothing.
- A step in the back row. Next to New England aster 'Alma Pötschke' (3½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- 3 plants in one group. Massed, one kind reads as a single shape. Scattered, it would look spotty.
Why now
- In flower for 7 weeks. From late August to early October.
- Fills a gap. For one of those weeks nothing else on the plan is in flower.
Planned as an English border: 4 of the 4 groups (100%) are drifts, longer along the bed than they are deep. The bed is balanced: the left half carries 50% of the visual weight and the right half 50%. Pink runs through the planting: 3 of the 6 kinds grown for their flowers have it.
The planner's own design check: 13 Excellent, 3 Good, 1 Satisfactory. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where ironweed 'Iron Butterfly' goes in a border
At 2½ ft it belongs in the middle of a bed. In the planner's ten height classes it is medium tall (2½ to 3 ft).
Its job: drift. Planted in a small group of three or five, and repeated further along in the other number.
A handsome foliage plant from spring, then a dome of purple when the garden needs it. The fine texture contrasts with sedums and coneflowers.
- Fine texture all season
- Late purple for dry soil
- Low-maintenance planting
What to plant with ironweed 'Iron Butterfly'
Plants recorded as good partners for it, and what each pairing does:
- Little bluestem: its blue-green leaves are a setting for the flowers, before and after; happy in the same dry soil.
- Sedum 'Autumn Joy': in flower together for seven weeks, from late August; bold leaves against its fine ones; happy in the same dry soil.
- Goldenrod 'Fireworks': purple against yellow, opposite each other on the colour wheel, in flower together for six weeks.
Questions about ironweed 'Iron Butterfly'
Does ironweed 'Iron Butterfly' need sun or shade?
Ironweed 'Iron Butterfly' grows in full sun (6 or more hours of direct sun a day).
It wants dry, sharply drained soil, on the lean side, with no feeding, and little watering once settled. Once settled in, it stands drought.
What zones does ironweed 'Iron Butterfly' grow in?
USDA zones 4 to 9. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does ironweed 'Iron Butterfly' flower in my zone?
In zone 5 it flowers late August to early October. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 4 | Late August to early October |
|---|---|
| Zone 5 | Late August to early October |
| Zone 6 | Late August to early October |
| Zone 7 | Mid August to early October |
| Zone 8 | Mid August to early October |
| Zone 9 | Early August to early October |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should ironweed 'Iron Butterfly' be planted?
24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 2½ ft (80 cm), so a group knits into one patch.
It grows 2½ ft (80 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many ironweed 'Iron Butterfly' plants do I need?
At 24 in apart, set out in staggered rows:
- 3 to fill 10 square feet (about 1 m²)
- 6 for a single row 10 ft (3 m) long
- 10 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as a group of three or five, with a second group further along in the other number.
In the bed above, the planner used three in one group.
Is ironweed 'Iron Butterfly' poisonous to dogs and cats?
No toxicity is recorded for dogs, cats, horses or people, according to NC State Extension.
"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.
Do deer eat ironweed 'Iron Butterfly'?
Mostly not. NC State lists it as resistant to deer and rabbits. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.
What flowers after ironweed 'Iron Butterfly'?
Ironweed 'Iron Butterfly' is over by early October. These start as it finishes and carry the same spot on, so it never goes flat:
- Chrysanthemum 'Sheffield Pink': from late September to early November, 2½ ft tall.
- Japanese onion 'Ozawa': from early October to early November, 10 in tall, to stand in front of it and cover its fading stems.
- Tatarian aster 'Jindai': from early October to early November, 4 ft tall.
What does ironweed 'Iron Butterfly' look like in winter?
Ironweed 'Iron Butterfly' dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.
Is ironweed 'Iron Butterfly' good for bees and butterflies?
Ironweed 'Iron Butterfly' is visited by bees, butterflies and hummingbirds.
It is native to the United States (this is a named variety of the native plant).
More Vernonia
- New York ironweed Vernonia noveboracensis
In these guides
- Plants for slopes and banks
- Deer-resistant perennials for full sun
- Rabbit-resistant plants
- Drought-tolerant perennials for full sun
- Pet-safe plants for a sunny border
- Native perennials for pollinators
- Plants for hummingbirds
- Plants for butterflies
- Plants for bees
- Plants that flower in fall
Zone guides: Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8 · Zone 9
Every fact on record
- Type
- Perennial
- Size
- 2½ ft (80 cm) tall, 2½ ft (80 cm) wide
- Plant
- 24 in (60 cm) apart
- Height class
- Medium tall (2½ to 3 ft)
- Place in the bed
- Middle
- Flowers
- Late August to early October; dense clusters; purple
- Leaves
- Fine texture, herbaceous; green
- Shape
- Mounding, clumping
- Hardy in
- USDA zones 4 to 9
- Light
- Full sun
- Soil
- Lean, dry and sharply drained
- Water
- Low
- Feeding
- None needed
- Family
- Asteraceae
- Comes from
- Arkansas and Oklahoma
- Attracts
- Bees, butterflies, hummingbirds
- Stands up to
- Deer, rabbits, drought, erosion
Checked against NC State Extension. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.