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garden
Ironweed
Cyanthillium
Overview
A tall native perennial named for its impossibly sturdy stems, ironweed produces brilliant violet-purple flower clusters in late summer that are magnets for butterflies and bees. Growing 4-7 feet tall, it makes a dramatic statement at the back of borders and in naturalized meadow plantings. Despite its tough reputation, ironweed has a graceful presence and combines beautifully with goldenrod and native grasses.
Growing Conditions
Hardiness Zones5 — 9
Height22.1m
Spread0.75m
Growth HabitForb/herb
Pollinator Valuehigh
Companion Planting & Soil
Good Companions
Soil pH5.5 — 7
Soil TypeMoist, fertile soil; tolerates clay and periodic wet conditions
Planting Calendar
When to sow, transplant, and harvest by growing zone.
| Zone | Action | Months | Notes |
|---|---|---|---|
| Cold (1-2) | Transplant | May — Jun | Plant in spring; native perennial; grows 3-8 feet tall depending on species |
| Cold (1-2) | Bloom | Aug — Sep | Vivid purple flowers in late summer; important late-season pollinator plant |
| Cool (3-4) | Transplant | Apr — May | Plant in spring; tolerates wet soil; vivid purple flowers |
| Cool (3-4) | Bloom | Jul — Sep | Mid to late summer bloom; combines well with goldenrod |
| Moderate (5-7) | Transplant | Mar — Apr | Plant in spring; back of border or meadow planting; very tough |
| Moderate (5-7) | Bloom | Jul — Sep | Late summer bloom; pinch in June for shorter, bushier plants |
| Moderate (5-7) | Divide | Mar — Apr | Divide every 4-5 years in early spring if clumps get too large |
| Warm (8-9) | Transplant | Feb — Mar | Plant in late winter/spring |
| Warm (8-9) | Bloom | Jun — Sep | Extended bloom; attracts swallowtails and painted ladies |
| Hot (10+) | Transplant | Nov — Dec | Plant in fall; heat tolerant |
| Hot (10+) | Bloom | Jun — Aug | Summer bloom; tolerates heat and drought |
Uses
Other Uses
- Striking late-season pollinator magnet
- Back-of-border native perennial with strong vertical form
- Streamside and rain garden plantings
