Iroquois, South Dakota, sits in USDA hardiness zone 4b — a zone band wide enough that plant choice, not possibility, is the interesting question.
On paper, cabbage, cranberry, turkish rocket, and collard greens all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Even in Iroquois, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Iroquois lot. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Iroquois — soil, climate, flood, and parcel records. How we handle your address.
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Iroquois — the short answer
Iroquois, South Dakota: USDA zone 4b, about 175 days between hard freezes, across 397 acres of city.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 21
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 13
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~175
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 397 acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 4b is Iroquois's average, not your lot's — a low corner or a tree line moves it. Against Iroquois's 175-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Iroquois
Each reading below is measured for Iroquois itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredIroquois runs about 175 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredIroquois sits in USDA hardiness zone 4b.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Iroquois is in
Iroquois sits in the Northern Glaciated Plains — EPA Level III, inside the wider Great Plains. That is read at Iroquois's own centroid rather than borrowed from Kingsbury County.
What Grows in Iroquois
Every plant below cleared Iroquois's own zone 4b and its 175-day season. Each card opens that plant's South Dakota profile. How we score.
Is it too late to plant in Iroquois?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Mar 24; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 21 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 13 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
What's on the federal record near Iroquois
Closest first, within ~10 miles of Iroquois. Listing isn't leaking, and distance isn't exposure.
- IROQUOIS IRONWORKER, INC.Brownfields · 350 ft
- 110N58W 6BBBA (2)Nitrate · 500 ft
- CHARLES FLOWERSUnderground Storage Tanks · 1000 ft
- BIEVER BULK SALES COUnderground Storage Tanks · 1000 ft
- 110N59W 1AACBNitrate · 2300 ft
- 111N59W36DCDDNitrate · 2400 ft
- 111N59W36DDCCNitrate · 2400 ft
- 110N58W 6CBBBNitrate · 2400 ft
- 110N58W 6CBBB2Nitrate · 2400 ft
- 111N59W25CDDDNitrate · 1.3 mi
- 110N59W 2DDDDNitrate · 1.5 mi
- 110N59W10DAAA (2)Nitrate · 2.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Iroquois's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Iroquois.
Sources Checked
within ~10 miles of Iroquois
Severity Distribution
within ~10 miles of Iroquois
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Iroquois, Nitrate runs higher than the national average — 104 sites within ~10 miles of Iroquois. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Iroquois
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the Iroquois average
Your land is one point inside Iroquois
Everything above resolves to Iroquois as a whole — one PHZM band and one 28°F frost record, read across 397 acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at city scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better local average.
Your Lot vs the Iroquois Average
Iroquois Average
- ●USDA Zones 4b, averaged across Iroquois
- ●One soil character for all of Iroquois
- ●Frost dates read at Iroquois's scale: Apr 21 to Oct 13
YOUR Parcel
- ✓Your exact zone, not Iroquois's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Iroquois
Pull a site-specific report for your exact address in Iroquois, South Dakota — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Iroquois averages can't show:
We read public map data around Iroquois — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Iroquois average
How we know this about Iroquois
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Iroquois’s own record; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at city grain anywhere on this page — there is no city-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Iroquois
When does frost risk typically end in Iroquois?
The last hard freeze (28°F) in Iroquois typically lands around Apr 21, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about May 12.
When is the first frost in Iroquois?
The first hard freeze (28°F) in Iroquois typically arrives around Oct 13, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 29, so the watching starts about Sep 13 — about 175 days after the spring freeze cleared.
How long is the growing season in Iroquois?
Measured between 28°F hard freezes, Iroquois sees about 175 frost-free days — roughly Apr 21 through Oct 13, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 12 to Sep 29, about 140 days.
Is the soil safe to grow vegetables in Iroquois?
The federal record around Iroquois shows 111 documented sites, mostly Nitrate entries (104), the nearest Brownfields record under a tenth of a mile out — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.
How do I protect my plants from frost in Iroquois?
From about Sep 13 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Oct 13 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Oct 13. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Iroquois's scale — its 4b band and its 175-day season. Your yard writes its own version of Iroquois's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Iroquois’s own scale
6 of the readings below were taken at Iroquois's own scale — its own ~175-day season between 28°F freezes, the 397 acres it covers and 111 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Iroquois's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Iroquois's own 28°F hard-freeze dates, about Apr 21 and Oct 13 and the ~175-day span between themNOAA 1991–2020 Climate Normals
- 111 documented contamination sites on the federal record near Iroquois, the closest Brownfields record under a tenth of a mile out from the town centreFederal environmental registers
- Iroquois's boundary and the 397 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~175-day seasonGrowable Ground crop-matching engine
- The ecoregion at Iroquois's own centroid, the Northern Glaciated PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Iroquois's 397 acres read through its county's SSURGO summaryfrom Kingsbury County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Kingsbury County
- The growing challenges every South Dakota grower plans around — written at state scale, so they stay on the state guidefrom South Dakota
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Kingsbury County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Iroquois's 397 acreswhy one lot differs from the next →
- Which side of Iroquois you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 397 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields record under a tenth of a mile out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Iroquois-wide figureread your own land →
More in South Dakota
Wider growing context
What grows across South DakotaIroquois sits outside our named growing regions, so South Dakota as a whole is its closest context here.
Nearby growing guides