Unlikely — Zone Mismatch
swamp sunflower (zones 6-9) does not overlap with North Dakota's zone range (3b-4b). Growing outdoors is unlikely without significant protection.
One zone short — what would close it
Swamp Sunflower is hardy to zone 6, and the warmest ground in North Dakota is zone 5 — 1 zone short. Planted in open ground it will not survive a North Dakota winter. To grow it here, grow swamp sunflower in a container and move it under cover for the coldest weeks, or give it a greenhouse.
Season extension and overwintering under cover both work at this margin. How to buy the weeks →
Zone math from 6-9 (plant) against 3-5 (North Dakota). Lift modeled by crop_engine Sprint 20B effective_zone_modifier (+2 zones) via api/fast_sections.py Unlock Engine v2.
Your yard isn't the whole zone.
North Dakota spans zones 3b-4b, but your yard sits in exactly one — and slope, tree cover, and cold-air pockets nudge it further. Enter your address and we'll score swamp sunflower against your parcel's actual hardiness, soil, and sun.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Zone Comparison
Swamp Sunflower Needs
- USDA Zones: 6-9
- Frost-Free Days: 70+
- Sun: Full Sun
- Mature size: 6 ft tall
- Picking window: ~45 days of harvest
- Drought tolerance: Medium
North Dakota Has
- USDA Zones: 3b-4b
- Last Hard Freeze (28°F): Apr 30 - May 6
- First Hard Freeze (28°F): Oct 4 - Oct 9
- Annual Rainfall: 14-22 inches
- Common Soils: Prairie loam, Clay (Red River Valley), Sandy loam
Plant Zone Range (zones 6-9)
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Swamp Sunflower in North Dakota
The frost window
Across North Dakota, the last spring hard freeze (28°F) clears between Apr 30 and May 6, and the first fall hard freeze lands between Oct 4 and Oct 9 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 151-day window you can count on — up to 162 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
Winter standing
North Dakota runs as cold as USDA zone 3, and no sourced winter-hardiness floor is on record for swamp sunflower, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether swamp sunflower is a permanent planting or a replant-every-spring crop for you turns on your own zone within North Dakota; check its hardiness range against that before treating it as long-lived ground.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
The zone check says swamp sunflower does not survive a North Dakota winter in the ground. The season figures below measure a different question — whether it could finish a season here at all — and they only bear on North Dakota under protection.
Frost-free days
Swamp Sunflower wants 70+ frost-free days; a typical North Dakota site sees ~157 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Swamp Sunflower likes near-neutral soil (pH 5.5-8). That's the common-ground band across North Dakota's prairie loam and clay (red river valley) — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 6 and 7.5 — worth knowing before you decide whether a North Dakota soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your North Dakota site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
SSURGO maps about 20.3% of North Dakota as poorly or somewhat-poorly drained, and the class flips parcel to parcel. Swamp Sunflower sits mid-range for drought tolerance, so either extreme can cost you — your soil map unit, not the state average, is the real answer.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. North Dakota soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Swamp Sunflower in North Dakota — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 6-9 (USDA PLANTS Database)
- State Zones: 3b-4b (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Apr 30 - May 6 to Oct 4 - Oct 9 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Swamp Sunflower in North Dakota
Zone compatibility tells you about winter cold survival — but North Dakota growers also need to think about:
Extreme cold (-40F) and short growing season
Persistent wind desiccates plants
Low rainfall in western ND
Growing swamp sunflower here specifically
Swamp Sunflower rates to USDA zones 6–9 and is hardy to about 41°F, but cold isn't the risk in North Dakota — wet is: with roughly 20.3% of its soils poorly-drained (SSURGO), soggy ground rots the crown.
Give swamp sunflower a raised bed or mounded row with coarse amendment so its crown never sit wet. How to handle it →
What to actually do about these — and the constraints that apply to every North Dakota grower, not just swamp sunflower — is covered on the North Dakota growing guide.
Timing shifts within North Dakota
Swamp Sunflower needs about 70 days of frost-free season to complete its cycle. Even Bottineau County — North Dakota’s shortest season at 141 frost-free days — clears that by 71 days, so season length isn’t the constraint anywhere in North Dakota. What varies is your own parcel.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Swamp Sunflower's 70-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Swamp Sunflower draws honeybees, native bees, and butterflies (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, swamp sunflower can only work that bloom inside North Dakota's frost window — roughly 157 days, opening after the last 28°F freeze (Apr 30 - May 6) and closing at the first (Oct 4 - Oct 9), per NOAA Regional Climate Centers ACIS, 1991-2020.
Recommended Swamp Sunflower Varieties for North Dakota
North Dakota publishes no state variety trial for swamp sunflower, so we won't invent a "best for North Dakota" list. Choose types rated to your USDA hardiness zone (3b-4b), and confirm winter survival and drainage against your own parcel.
North Dakota Cooperative Extension
For North Dakota-specific cultivar recommendations, planting calendars, and pest pressure for swamp sunflower, the canonical source is NDSU Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Swamp Sunflower native to North Dakota?
Swamp Sunflower is native to parts of the Lower 48, but the USDA PLANTS Database (accessed 2026-07-01) does not document a native range in North Dakota. It can still earn a place in a North Dakota garden — the zone comparison above tells you whether it will thrive.
Looking for plants that belong here? The North Dakota growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Swamp Sunflower in North Dakota
When can I plant Swamp Sunflower in North Dakota?
North Dakota's last spring hard freeze (28°F) clears between Apr 30 and May 6, and the first fall hard freeze lands between Oct 4 and Oct 9 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Swamp Sunflower, so this page does not state whether it overwinters in North Dakota and publishes no fall establishment date for it — check its hardiness range against your own zone before treating it as a permanent planting.
What hardiness zone is Swamp Sunflower grown in across North Dakota?
North Dakota spans USDA hardiness zones 3b-4b (USDA ARS PHZM 2023). Swamp Sunflower carries a range of zones 6-9, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical North Dakota site have?
A typical North Dakota site sees ~157 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Swamp Sunflower needs 70+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Swamp Sunflower native to North Dakota?
Swamp Sunflower is native to parts of the Lower 48, but the USDA PLANTS Database (accessed 2026-07-01) does not document a native range in North Dakota. It can still earn a place in a North Dakota garden — the zone comparison above tells you whether it will thrive.
How should I amend the soil for Swamp Sunflower in North Dakota?
Swamp Sunflower prefers pH 5.5-8 and well (dry spells) drainage (FAO ECOCROP). That sits in the common-ground band across North Dakota soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Swamp Sunflower actually grow on my specific land in North Dakota?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores swamp sunflower against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in North Dakota
State-level data is a sketch. Your Growable Ground report scores swamp sunflower against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that North Dakota swamp sunflower averages can't show:
We read public map data around North Dakota — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the North Dakota swamp sunflower average
Explore More
Growing guides for swamp sunflower
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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