Unlikely — Zone Mismatch
scarlet runner bean (zones 7-11) does not overlap with Iowa's zone range (4b-6a). Growing outdoors is unlikely without significant protection.
One zone short — what would close it
Scarlet Runner Bean is hardy to zone 7, and the warmest ground in Iowa is zone 6 — 1 zone short. Planted in open ground it will not survive a Iowa winter. To grow it here, grow scarlet runner bean 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 7-11 (plant) against 4-6 (Iowa). 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.
Iowa spans zones 4b-6a, 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 scarlet runner bean against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Scarlet Runner Bean Needs
- USDA Zones: 7-11
- Frost-Free Days: 70+
- Sun: Full Sun
- Mature size: 12 ft tall
- Picking window: ~60 days of harvest
- Drought tolerance: Low
Iowa Has
- USDA Zones: 4b-6a
- Last Hard Freeze (28°F): Apr 10 - Apr 17
- First Hard Freeze (28°F): Oct 18 - Oct 23
- Annual Rainfall: 26-36 inches
- Common Soils: Prairie loess, Silt loam, Clay loam
Plant Zone Range (zones 7-11)
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 Scarlet Runner Bean in Iowa
The frost window
Across Iowa, the last spring hard freeze (28°F) clears between Apr 10 and Apr 17, and the first fall hard freeze lands between Oct 18 and Oct 23 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 184-day window you can count on — up to 196 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
Iowa runs as cold as USDA zone 4, and no sourced winter-hardiness floor is on record for scarlet runner bean, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether scarlet runner bean is a permanent planting or a replant-every-spring crop for you turns on your own zone within Iowa; check its hardiness range against that before treating it as long-lived ground.
Timing tuned to sub-state frost dates — Howard County, not the statewide average.
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 scarlet runner bean does not survive a Iowa 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 Iowa under protection.
Frost-free days
Scarlet Runner Bean wants 70+ frost-free days; a typical Iowa site sees ~189 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Scarlet Runner Bean needs ~900 GDD (base 50°F) to ripen. The state median runs ~2730 GDD (from PRISM 1991-2020 climate normals), so Iowa's typical season clears that easily.
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
Scarlet Runner Bean likes near-neutral soil (pH 5.5-7.5). That's the common-ground band across Iowa's prairie loess and silt loam — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 6 and 7 — worth knowing before you decide whether a Iowa soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Iowa site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Iowa's soils run mostly silty clay loam, but SSURGO maps the series, texture, and drainage under your exact parcel. What matters for scarlet runner bean is the horizon its roots actually work, not the surface. That map unit, not the state average, decides how scarlet runner bean performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Iowa soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Scarlet Runner Bean in Iowa — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 7-11 (USDA PLANTS Database)
- State Zones: 4b-6a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Apr 10 - Apr 17 to Oct 18 - Oct 23 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Scarlet Runner Bean in Iowa
Zone compatibility tells you about winter cold survival — but Iowa growers also need to think about:
Cold winters reaching -20F or below
Variable spring weather delays planting
Wind exposure on open prairies desiccates plants
Growing scarlet runner bean here specifically
Iowa's soils run mostly silty clay loam (Mollisols), and whether that suits scarlet runner bean's pH 5.5–7.5 preference comes down to your exact parcel, not the statewide picture.
Pull your parcel's SSURGO map unit, test pH, and amend toward scarlet runner bean's 5.5–7.5 target before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Iowa grower, not just scarlet runner bean — is covered on the Iowa growing guide.
Timing shifts within Iowa
Iowa isn't one climate. In Howard County, the last hard freeze (28°F) holds until about Apr 24 — roughly 10 days later than the recorded state median — so plant scarlet runner bean to your county's window, not the statewide date.
Scarlet Runner Bean needs about 70 days of frost-free season to complete its cycle. Even Howard County — Iowa’s shortest season at 168 frost-free days — clears that by 98 days, so season length isn’t the constraint anywhere in Iowa. 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"). Scarlet Runner Bean'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
Scarlet Runner Bean draws honeybees, native bees, and hummingbirds (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, scarlet runner bean can only work that bloom inside Iowa's frost window — roughly 189 days, opening after the last 28°F freeze (Apr 10 - Apr 17) and closing at the first (Oct 18 - Oct 23), per NOAA Regional Climate Centers ACIS, 1991-2020.
Iowa Cooperative Extension
For Iowa-specific cultivar recommendations, planting calendars, and pest pressure for scarlet runner bean, the canonical source is Iowa State University Extension and Outreach. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Scarlet Runner Bean native to Iowa?
No — the USDA PLANTS Database lists Scarlet Runner Bean as introduced rather than native in the Lower 48, so it is not part of Iowa's native flora. It grows here as a garden plant; pairing it with a few Iowa natives keeps local pollinators fed too.
Looking for plants that belong here? The Iowa 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 Scarlet Runner Bean in Iowa
When can I plant Scarlet Runner Bean in Iowa?
Iowa's last spring hard freeze (28°F) clears between Apr 10 and Apr 17, and the first fall hard freeze lands between Oct 18 and Oct 23 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Scarlet Runner Bean, so this page does not state whether it overwinters in Iowa 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 Scarlet Runner Bean grown in across Iowa?
Iowa spans USDA hardiness zones 4b-6a (USDA ARS PHZM 2023). Scarlet Runner Bean 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 Iowa site have?
A typical Iowa site sees ~189 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Scarlet Runner Bean needs 70+ 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 Howard, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Scarlet Runner Bean native to Iowa?
No — the USDA PLANTS Database lists Scarlet Runner Bean as introduced rather than native in the Lower 48, so it is not part of Iowa's native flora. It grows here as a garden plant; pairing it with a few Iowa natives keeps local pollinators fed too.
How should I amend the soil for Scarlet Runner Bean in Iowa?
Scarlet Runner Bean prefers pH 5.5-7.5 and well (dry spells) drainage (Growable Ground Plant Database). That sits in the common-ground band across Iowa soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Scarlet Runner Bean actually grow on my specific land in Iowa?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores scarlet runner bean 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 Iowa
State-level data is a sketch. Your Growable Ground report scores scarlet runner bean against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Iowa scarlet runner bean averages can't show:
We read public map data around Iowa — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Iowa scarlet runner bean average
Explore More
Growing guides for scarlet runner bean
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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