Ironweed is a perennial grown for its purple blooms, which open in late summer and return year after year. It's hardy across USDA zones 4 through 8. Its late summer flowers are a real draw for honeybees, native bees, and butterflies.
Zones
4-8
pH Range
5-7.5
Sun
Full Sun
Days to Maturity
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Score Ironweed on your exact land.
Zone averages can't see the slope, soil, frost, and sun that decide whether ironweed actually takes — and those shift from one yard to the next. Enter your address and we'll score ironweed against your land's real conditions.
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What Ironweed is
Ironweed grows as a perennial. It blooms purple in late summer.
How to grow Ironweed
Ironweed grows in USDA zones 4 through 8. Ironweed does best in full sun — at least 6 hours of direct sun a day — and soil from pH 5 to 7.5, on well-drained ground. It needs a growing season of at least 365 frost-free days, which is why climate matters as much as soil.
USDA Zones
4-8
USDA PHZM 2023
Soil pH
5 - 7.5
USDA PLANTS Database
Sun
Full Sun
plant_species_v5.csv
Drainage
well (dry spells)
plant_species_v5.csv
Frost Tolerance
60.8°F
plant_species_v5.csv
Frost-Free Days
365+
plant_species_v5.csv
Start the season right
Plant ironweed in full sun with at least 6 hours of direct sun, once the soil has warmed and frost risk has passed.
Match the soil
Ironweed prefers pH 5 to 7.5 (USDA PLANTS Database). A quick soil test from your local Extension lab tells you whether to add lime or sulfur to land in band.
Water steadily
Keep the root zone evenly moist through establishment. A 2–3 inch mulch layer holds moisture without waterlogging.
Harvest at its peak
Cut ironweed blooms in the cool of the morning, just as they open, for the longest display.
Good to know
Good news for pet owners — ironweed isn't known to be toxic to dogs or cats. (Source: ASPCA.)
Ironweed is a standout pollinator plant — high value to bees and other pollinators. (Source: Xerces Society, Pollinator Partnership.)
Where Ironweed thrives
Ironweed is hardy across USDA zones 4 through 8. Zone is only the starting point, though: the soil pH, drainage, and frost dates on your specific land decide how well it actually does.
Zones 4–8·Where Ironweed growsOpen map →
On USDA hardiness-zone overlap, Ironweed can grow in these states:
See if Ironweed will thrive on your land
Zone averages are a start. Your exact soil pH, drainage, sun exposure, and frost dates shape whether ironweed actually takes — we score it against the real conditions at your address.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Frequently Asked Questions
Can I grow Ironweed in my zone?
Ironweed grows in USDA hardiness zones 4 through 8 (USDA PHZM 2023). Zone is one factor — soil pH, drainage, and frost dates on your specific parcel also shape whether it takes.
When should you plant Ironweed?
Most growers plant ironweed after the last spring frost, once the soil has warmed, leaving enough of the season for its 365-day frost-free need. Your local frost dates set the exact window — a Growable Ground report reads them for your address.
How much sun does Ironweed need?
Ironweed needs full sun — a spot that catches at least 6 hours of direct summer sun a day. In more shade it still grows, but usually gives a smaller, later crop. The catch is that a yard rarely gets even light everywhere — a fence, the house, or one tall tree can quietly take those hours. A Growable Ground report reads the real sun-hours across your land, canopy and buildings included, so you can pick the brightest bed before you plant.
What soil does Ironweed need?
Ironweed prefers soil pH 5 to 7.5, on well-drained ground (USDA PLANTS Database). Your report scores your parcel's actual soil against that using USDA SSURGO data.
Does Ironweed attract pollinators?
Yes — ironweed's flowers are a strong nectar and pollen source for honeybees, native bees, and butterflies (Xerces Society, Pollinator Partnership).
Is Ironweed safe for pets?
Ironweed is not known to be toxic to dogs or cats based on available data (ASPCA). Always supervise pets around new plantings.