New York ironweed
Vernonia noveboracensis · Asteraceae
Flat clusters of the most intense, saturated purple in late summer, on stems above head height. The name refers to its iron-hard stems.
- Size
- 6½ ft tall, 3 ft wide
- Zones
- 5 to 9
- Light
- Full sun
- Flowers
- Early August to mid September
- Pets
- No toxicity recorded
- Job in a bed
- Specimen
A bed built around New York ironweed
The planner designed this bed around New York ironweed when this page was made: a 12 × 6 ft (3.7 × 1.8 m) cottage garden in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why New York ironweed stands where it does.
The plants
- 1 New York ironweed × 1, purple
- 2 Creeping phlox 'Emerald Blue' × 5, blue
- 3 Cheddar pinks 'Firewitch' × 11, pink
- 4 Sneezeweed 'Sahin's Early Flowerer' × 3, orange
- 5 Stiff goldenrod × 3, yellow
- 6 Palm sedge × 3, green leaves
- 7 Ornamental onion 'Purple Sensation' × 5, purple
- 8 Snowdrop × 10, white
Why this plant
- The only dense clusters. The others are open bowls, daisies, flat plates and others. Shape reads at a distance, where colours blur.
Why here
- Anchors a back corner. At 6½ ft it is the tallest plant 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 sneezeweed 'Sahin's Early Flowerer' (3 ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- One plant, alone. A feature plant is seen as an object, and needs clear ground around it.
Why now
- In flower for 7 weeks. From early August to mid September.
- Part of the bed's peak. With sneezeweed 'Sahin's Early Flowerer' and stiff goldenrod in mid August: 3 kinds at once. No week has more.
Planned as a cottage garden: 26 of the 26 plants (100%), bulbs aside, stand alone or in groups of no more than five, small enough for the kinds to mingle. The flowering year starts with snowdrop in early March and ends with sneezeweed 'Sahin's Early Flowerer' in early October. The longest in flower is sneezeweed 'Sahin's Early Flowerer': 15 weeks, from late June to early October.
The planner's own design check: 12 Excellent, 4 Good, 1 Needs revision. Its weakest point is height and scale: Heights average about 6 in at the front, 22 in in the middle and 4 ft at the back. Along the back row the heights step up and down, between 3 ft and 6½ ft, and no two neighbours are the same height. 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 New York ironweed goes in a border
At 6½ ft it belongs at the back of a bed. In the planner's ten height classes it is very tall (5 to 6½ ft).
Its job: specimen. A feature plant with a shape of its own. It stands alone with room around it, and repeats only at a distance.
No other late-summer plant has this depth of purple. It is superb with the yellows of the season. Cut it back by half in June to keep it shorter.
- Late purple at the back of a large border
- Moist meadows and rain gardens
- Butterfly gardens
What to plant with New York ironweed
Plants recorded as good partners for it, and what each pairing does:
- Joe Pye weed 'Gateway': in flower together for six weeks, from early August; bold leaves against its medium ones; happy in the same moist soil.
- Sunflower 'Lemon Queen': purple against yellow, opposite each other on the colour wheel, in flower together for seven weeks.
- Switchgrass 'Shenandoah': its green leaves are a setting for the flowers, before and after; low enough (4 ft) to stand in front of it.
Questions about New York ironweed
Does New York ironweed need sun or shade?
New York ironweed grows in full sun (6 or more hours of direct sun a day).
It wants soil that stays evenly moist, of average fertility, and a good soak in dry spells. It copes with soil that stays wet.
What zones does New York ironweed grow in?
USDA zones 5 to 9. It is hardy to zone 5, which means it survives winter nights down to about −10 °F (−23 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does New York ironweed flower in my zone?
In zone 5 it flowers early August to mid September. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 5 | Early August to mid September |
|---|---|
| Zone 6 | Early August to mid September |
| Zone 7 | Early August to mid September |
| Zone 8 | Early August to mid September |
| Zone 9 | Late July to mid September |
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 New York ironweed be planted?
2½ ft (75 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 3 ft (90 cm), so a group knits into one patch.
It grows 6½ ft (200 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many New York ironweed plants do I need?
At 2½ ft apart, set out in staggered rows:
- 2 to fill 10 square feet (about 1 m²)
- 5 for a single row 10 ft (3 m) long
- 6 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as one, with clear ground around it: a feature plant is seen as an object, and a group of them is a thicket.
In the bed above, the planner used one in one group.
Is New York ironweed 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 New York ironweed?
Mostly not. NC State lists it as resistant to deer. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.
Will New York ironweed spread?
It seeds itself about; the risk of it taking over is moderate. Self-seeds freely. Remove the spent flowers to limit seedlings.
What flowers after New York ironweed?
New York ironweed is over by mid September. These start as it finishes and carry the same spot on, so it never goes flat:
- Garden chrysanthemum: from mid September to late October, 24 in tall, to stand in front of it and cover its fading stems.
- Swamp sunflower: from late September to late October, 6½ ft tall.
- Montauk daisy: from mid September to late October, 3 ft tall, to stand in front of it and cover its fading stems.
What does New York ironweed look like in winter?
New York ironweed dies down, but leave the stems standing: the seed heads stand through the winter, and songbirds eat the seed. Cut them down in early spring, before the new shoots come.
Is New York ironweed good for bees and butterflies?
New York ironweed is visited by pollinators, bees, specialist bees, butterflies and songbirds.
It is native to the United States.
More Vernonia
- Ironweed 'Iron Butterfly' Vernonia lettermannii 'Iron Butterfly'
In these guides
- Plants for wet soil and rain gardens
- Deer-resistant perennials for full sun
- Pet-safe plants for a sunny border
- Native perennials for pollinators
- Plants for butterflies
- Plants for bees
- Plants that feed garden birds
- Tall perennials and grasses for the back of a border
Every fact on record
- Type
- Perennial
- Size
- 6½ ft (200 cm) tall, 3 ft (90 cm) wide
- Plant
- 2½ ft (75 cm) apart
- Height class
- Very tall (5 to 6½ ft)
- Place in the bed
- Back
- Flowers
- Early August to mid September; dense clusters; purple
- Leaves
- Medium texture, herbaceous; dark green
- Shape
- Upright, self-seeding
- Hardy in
- USDA zones 5 to 9
- Light
- Full sun
- Soil
- Average, evenly moist
- Water
- Moderate
- Feeding
- None needed
- Family
- Asteraceae
- Comes from
- Eastern and southeastern United States
- Attracts
- Pollinators, bees, specialist bees, butterflies, songbirds
- Stands up to
- Deer, wet soil
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.