Unlikely — Zone Mismatch
sunn hemp (zones 7-11) does not overlap with South Dakota's zone range (4a-5b). Growing outdoors is unlikely without significant protection.
2 zones short — what would close it
Sunn Hemp is hardy to zone 7, and the warmest ground in South Dakota is zone 5 — 2 zones short. Planted in open ground it will not survive a South Dakota winter. To grow it here, grow sunn hemp in an earth-sheltered greenhouse — its modeled 2.5-zone lift covers this gap.
An earth-sheltered greenhouse is the lift this needs. How a greenhouse changes what you can grow →
Zone math from 7-11 (plant) against 4-5 (South Dakota). Lift modeled by crop_engine.GREENHOUSE_ZONE_MODIFIER_BY_SUBTYPE['earth_sheltered'] (+2.5 zones) via api/fast_sections.py Unlock Engine v2.
Sunn Hemp in South Dakota — the short answer
Sunn Hemp in South Dakota: hardy in zones 7–11, full sun, against a state median of ~168 frost-free days.
- Plant zones
- 7-11
- 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
- South Dakota zones
- 4a-5b
- USDA PHZM 2023
- Frost window
- Apr 22 - Apr 29 – Oct 9 - Oct 15
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 145 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
- Days to maturity
- 90 days
- Growable Ground Plant Database
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — per-field provenance varies and is published with the dataset.
Your yard isn't the whole zone.
Sunn Hemp is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical South Dakota site runs ~168 frost-free days, but that is a state median, not your yard: slope, trees, and low spots move the last-frost date across a single parcel. Enter your address and we'll score sunn hemp against your land's actual frost dates, sun, and soil.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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South Dakota is not one climate
South Dakota’s winter-low ladder runs across 66 counties, from zone 4 in Brown County to zone 5.5 in Custer County. That is 15°F between the two counties’ average coldest night — the difference between sunn hemp overwintering in the ground and coming under cover.
The middle half of 66 counties runs 4.5–5 zones, with a median of 4.5 zones — a 1.5-zone span end to end.
Measured across 66 South Dakota counties. USDA PHZM 2023, per county. Quartiles are order statistics — every figure shown is a value a real county recorded, not an interpolation. Your own site sits somewhere inside this range; a parcel report resolves where.
Where Sunn Hemp Stands in South Dakota
Sunn Hemp is rated for zones 7–11 — a cold floor USDA puts at 0 to 10°F. No South Dakota county sits inside it, so in open ground this is a grown-under-cover plant here rather than a bed plant — which is a statement about South Dakota winters, not about sunn hemp.
Below the zone 7 floor
66 counties
- Brown County · zone 4a
- Marshall County · zone 4a
- Beadle County · zone 4b
3 of 66 shown
Winter cold is the limit here — the same plant works in a container that comes under cover.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. A zone is a 10°F band of average annual extreme minimum temperature, so the floor above is the band the plant's rating denotes, not a single measured kill point. Slope, shelter and cold-air drainage routinely move a site half a zone either way from its county figure — which is the part only your address resolves.
Zone Comparison
Sunn Hemp Needs
- USDA Zones: 7-11
- Frost-Free Days: 60+
- Sun: Full Sun
- Mature size: 6 ft tall
- Picking window: ~30 days of harvest
- Drought tolerance: Medium
South Dakota Has
- USDA Zones: 4a-5b
- Last Hard Freeze (28°F): Apr 22 - Apr 29
- First Hard Freeze (28°F): Oct 9 - Oct 15
- Annual Rainfall: 14-26 inches
- Common Soils: Prairie loam, Clay, Sandy loam
Plant Zone Range (zones 7-11)
Preferred Soil pH
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS, and university Extension sources — per-field provenance varies and is published with the dataset. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Sunn Hemp in South Dakota
The frost window
Across South Dakota, the last spring hard freeze (28°F) clears between Apr 22 and Apr 29, and the first fall hard freeze lands between Oct 9 and Oct 15 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 163-day window you can count on — up to 176 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.
When to start the seed
Sunn Hemp is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — South Dakota's dates above are the whole calendar for it. That makes the last-freeze date the binding constraint, and a warmer pocket of your own yard is worth more to this crop than it is to a transplanted one.
Days to maturity vs. the window
At 90 days to maturity (Growable Ground Plant Database), counting from the last hard freeze it ripens with 73 days to spare even in South Dakota's tightest freeze scenario — room for a later start or a second sowing.
Timing tuned to sub-state frost dates — Lawrence County, not the statewide average.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: Growable Ground Plant Database — frost-free days from FAO ECOCROP, days to harvest from university Extension production guides, and growing-degree-day and chill-hour minimums that are compilation estimates rather than published figures. 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 sunn hemp does not survive a South 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 South Dakota under protection.
Frost-free days
Sunn Hemp wants 60+ frost-free days; a typical South Dakota site sees ~168 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Sunn Hemp needs ~2200 GDD (base 50°F) to ripen. The state median runs ~2356 GDD (from PRISM 1991-2020 climate normals), so South Dakota sits right at the threshold — pay attention to siting and microclimate.
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
Sunn Hemp tolerates a wide pH range (pH 5-8.4) — 3.4 units, acid ground through alkaline — so soil acidity is rarely what limits it in South Dakota. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 6 and 7 — worth knowing before you decide whether a South Dakota soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your South 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
South Dakota's soils run mostly loam, but SSURGO maps the series, texture, and drainage under your exact parcel. Sunn Hemp needs about 19 inches of workable depth, so it is that horizon — not the surface — you are testing for. That map unit, not the state average, decides how sunn hemp performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH requirements: FAO ECOCROP and USDA PLANTS, with the remaining rows from other published sources or Growable Ground compilation. Drainage: FAO ECOCROP, with the remaining rows from other published sources or Growable Ground compilation. South Dakota soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
What Else to Consider for Sunn Hemp in South Dakota
Zone compatibility tells you about winter cold survival — but South Dakota growers also need to think about:
Extreme cold and short growing season
Low rainfall in western SD
Wind exposure on the open prairie
Growing sunn hemp here specifically
Sunn Hemp needs pH 5.0–8.4; South Dakota's dominant loam soils may or may not deliver that, so your parcel's SSURGO map unit is the real test.
Start with a soil test on your own ground and adjust pH and texture to fit sunn hemp's 5.0–8.4 range. How to handle it →
What to actually do about these — and the constraints that apply to every South Dakota grower, not just sunn hemp — is covered on the South Dakota growing guide.
Timing shifts within South Dakota
South Dakota isn't one climate. In Lawrence County, the last hard freeze (28°F) holds until about May 12 — roughly 17 days later than the recorded state median — so plant sunn hemp to your county's window, not the statewide date.
Sunn Hemp needs about 60 days of frost-free season to complete its cycle. Even Lawrence County — South Dakota’s shortest season at 145 frost-free days — clears that by 85 days, so season length isn’t the constraint anywhere in South 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"). Sunn Hemp's 60-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
Sunn Hemp draws honeybees, native bees, and butterflies (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, sunn hemp can only work that bloom inside South Dakota's frost window — roughly 168 days, opening after the last 28°F freeze (Apr 22 - Apr 29) and closing at the first (Oct 9 - Oct 15), per NOAA Regional Climate Centers ACIS, 1991-2020.
Good to Know Before You Plant Sunn Hemp
Sunn Hemp is listed as toxic to dogs, cats (seeds) at a moderate level (Cornell). Most listed plants only cause brief upset — a raised bed or a fenced corner usually keeps curious pets clear. Worth knowing for placement: in South Dakota this is a one-season plant and the first hard freeze (Oct 9 - Oct 15) takes it down, so the exposure above is a summer-long one rather than something standing in the bed all year.
South Dakota Cooperative Extension
For South Dakota-specific cultivar recommendations, planting calendars, and pest pressure for sunn hemp, the canonical source is SDSU Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Sunn Hemp native to South Dakota?
No — the USDA PLANTS Database lists Sunn Hemp as introduced rather than native in the Lower 48, so it is not part of South Dakota's native flora. It grows here as a garden plant; pairing it with a few South Dakota natives keeps local pollinators fed too.
Looking for plants that belong here? The South 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 Sunn Hemp in South Dakota
When can I plant Sunn Hemp in South Dakota?
South Dakota's last spring hard freeze (28°F) clears between Apr 22 and Apr 29, and the first fall hard freeze lands between Oct 9 and Oct 15 (NOAA Regional Climate Centers ACIS, 1991-2020). Time outdoor planting to after the last hard freeze for your specific site — a further two to three weeks for anything tender — and count back from those dates for transplant scheduling.
Can Sunn Hemp mature before first frost in South Dakota?
Yes — Sunn Hemp matures in 90 days (Growable Ground Plant Database), and South Dakota's dependable hard-freeze-free window runs 163 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 73 days of margin. Plant once the last hard freeze has passed — two to three weeks later for anything tender — and it ripens ahead of the first fall freeze.
What hardiness zone is Sunn Hemp grown in across South Dakota?
South Dakota spans USDA hardiness zones 4a-5b (USDA ARS PHZM 2023). Sunn Hemp carries a range of zones 7-11, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical South Dakota site have?
A typical South Dakota site sees ~168 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Sunn Hemp needs 60+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date. In cooler counties like Lawrence, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Sunn Hemp native to South Dakota?
No — the USDA PLANTS Database lists Sunn Hemp as introduced rather than native in the Lower 48, so it is not part of South Dakota's native flora. It grows here as a garden plant; pairing it with a few South Dakota natives keeps local pollinators fed too.
How should I amend the soil for Sunn Hemp in South Dakota?
Sunn Hemp tolerates pH 5-8.4 and well (dry spells) drainage (FAO ECOCROP). That is a 3.4-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a South Dakota site — amend for drainage and organic matter first.
Will Sunn Hemp actually grow on my specific land in South Dakota?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores sunn hemp 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 South Dakota
State-level data is a sketch. Your Growable Ground report scores sunn hemp against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that South Dakota sunn hemp averages can't show:
We read public map data around South Dakota — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the South Dakota sunn hemp average
Explore More
Growing guides for sunn hemp
Explore South Dakota county by county
South Dakota carries 66 counties with their own USDA zone — a sample of the growing pages for sunn hemp there:
Where else sunn hemp grows
Sunn Hemp's zone band crosses state lines — these are the states closest to South Dakota in winter climate where it also has a page, plus the far ends of its range. Each one re-answers the question with that state's own record.
More to grow in South Dakota
South Dakota has a growing page for 747 plants — a rotating sample of the rest of the shelf.
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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