Swamp Sunflower is a perennial grown for its yellow blooms, which open in late summer and return year after year. It's hardy across USDA zones 6 through 9. Its late summer flowers are a real draw for honeybees, native bees, and butterflies.
Zones
6-9
pH Range
5.5-8
Sun
Full Sun
Days to Maturity
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Score Swamp Sunflower on your exact land.
Zone averages can't see the slope, soil, frost, and sun that decide whether swamp sunflower actually takes — and those shift from one yard to the next. Enter your address and we'll score swamp sunflower against your land's real conditions.
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See Swamp Sunflower
What Swamp Sunflower is
Swamp Sunflower grows as a perennial and reaches around six feet at maturity. It blooms yellow in late summer.
How to grow Swamp Sunflower
Swamp Sunflower grows in USDA zones 6 through 9. Swamp Sunflower does best in full sun — at least 6 hours of direct sun a day — and soil from pH 5.5 to 8, on well-drained ground. It needs a growing season of at least 70 frost-free days, which is why climate matters as much as soil.
USDA Zones
6-9
USDA PHZM 2023
Soil pH
5.5 - 8
USDA PLANTS Database
Sun
Full Sun
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Drainage
well (dry spells)
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Frost Tolerance
41°F
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Mature Height
6 ft
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Frost-Free Days
70+
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Start the season right
Plant swamp sunflower in full sun with at least 6 hours of direct sun, once the soil has warmed and frost risk has passed.
Match the soil
Swamp Sunflower prefers pH 5.5 to 8 (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 swamp sunflower blooms in the cool of the morning, just as they open, for the longest display.
Good to know
Good news for pet owners — swamp sunflower isn't known to be toxic to dogs or cats. (Source: ASPCA.)
Swamp Sunflower is a standout pollinator plant — high value to bees and other pollinators. (Source: Xerces Society, Pollinator Partnership.)
Where Swamp Sunflower thrives
Swamp Sunflower is hardy across USDA zones 6 through 9. 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 6–9·Where Swamp Sunflower growsOpen map →
On USDA hardiness-zone overlap, Swamp Sunflower can grow in these states:
See if Swamp Sunflower will thrive on your land
Zone averages are a start. Your exact soil pH, drainage, sun exposure, and frost dates shape whether swamp sunflower 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 Swamp Sunflower in my zone?
Swamp Sunflower grows in USDA hardiness zones 6 through 9 (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 Swamp Sunflower?
Most growers plant swamp sunflower after the last spring frost, once the soil has warmed, leaving enough of the season for its 70-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 Swamp Sunflower need?
Swamp Sunflower 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 Swamp Sunflower need?
Swamp Sunflower prefers soil pH 5.5 to 8, on well-drained ground (USDA PLANTS Database). Your report scores your parcel's actual soil against that using USDA SSURGO data.
Does Swamp Sunflower attract pollinators?
Yes — swamp sunflower's flowers are a strong nectar and pollen source for honeybees, native bees, and butterflies (Xerces Society, Pollinator Partnership).
Is Swamp Sunflower safe for pets?
Swamp Sunflower is not known to be toxic to dogs or cats based on available data (ASPCA). Always supervise pets around new plantings.