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.
Swamp Sunflower — the short answer
Swamp Sunflower: grown in zones 6–9, full sun, pH 5.5–8.
- USDA zones
- 6–9
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- Soil pH
- 5.5–8
- FAO ECOCROP
- Sun
- Full Sun
- Growable Ground Plant Database
- Frost-kill temperature
- 32°F
- FAO ECOCROP
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — each tile names its own row's source, because per-field provenance varies.
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
FAO ECOCROP
Sun
Full Sun
Growable Ground plant catalog
Drainage
well (dry spells)
Growable Ground plant catalog
Frost Kill Temperature
32°F
Where cold starts killing growing tissue. Not a winter-survival floor — a dormant perennial takes far colder, which its hardiness zone answers.
FAO ECOCROP
Minimum Growing Temperature
41°F
Below this it stops growing rather than dies — a pace limit, not a survival limit.
FAO ECOCROP
Mature Height
6 ft
Growable Ground plant catalog
Frost-Free Days
70+
The frost-free stretch it needs start to finish — short-season areas may need an indoor head start.
Growable Ground plant catalog
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 (FAO ECOCROP). 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.
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.
A USDA zone is a 10°F band of average annual extreme winter minimum, so zones 6–9 spans average winter lows from -10°F to 30°F (USDA PHZM 2023). Across the 50 states and DC, that band covers 14 outright and splits 34 more down the middle — and which side of that line your land sits on changes the answer.
Zones 6–9·Where Swamp Sunflower growsOpen map →
Where Swamp Sunflower stands, state by state
Swamp Sunflower is rated for zones 6–9 — a cold floor USDA puts at -10 to 0°F. Across the 50 states and DC, 14 sit fully inside that band, the line runs through 34 more, and 3 sit outside it — and inside every split state, the same line runs on at county grain.
Fully inside zones 6–9
14 states
- Arkansas · zones 6b-8b
- Connecticut · zones 6a-7b
- Kentucky · zones 6a-7b
3 of 14 shown
The line runs through
34 states
3 of 34 shown
Swamp Sunflower’s band covers part of each of these states — which side of the line your county sits on changes the answer, and each state page draws it.
Outside zones 6–9
3 states
- Minnesota · zones 3a-5a
- North Dakota · zones 3b-4b
- South Dakota · zones 4a-5b
Winter cold is the limit here — the same plant often works in a container that comes under cover. Each link is that state’s own growing hub.
State zone extents: USDA Plant Hardiness Zone Map (PHZM) 2023. A zone is a 10°F band of average annual extreme minimum temperature, so a state that splits the band contains the boundary — its own page draws the county line, and a parcel report resolves which side your land sits on.
What grows around Swamp Sunflower
Growing guides for swamp sunflower
In rotation planning, swamp sunflower counts as a Other — beds recover best when other crops don’t follow each other in the same spot year over year. (Growable Ground derivation — crop-rotation group from botanical family)
Related plants in perennial flower
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.)
Your land is one point inside Swamp Sunflower's range
This page resolves to the species. Your state page draws the county line, and a report reads the parcel — the soil pH, drainage, sun, and frost dates on your exact ground, which no species average can see.
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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How we know this about Swamp Sunflower
The figures above are cited per row, not per site: the pH band names this plant’s own source column, the three temperature figures each carry their own, and days-to-maturity cites the publication that actually lists it. All of it comes from the Growable Ground Plant Database — a compilation over FAO ECOCROP, USDA PLANTS, and university Extension sources, published openly with per-field provenance.
Grounded inUSDA PLANTS Database•USDA PHZM•ASPCA
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 (FAO ECOCROP). 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. (Source: Xerces Society.)
Is Swamp Sunflower safe for pets?
Swamp Sunflower is not known to be toxic to dogs or cats based on available data. Always supervise pets around new plantings. (Source: ASPCA.)