Sioux County, in Iowa, sits in USDA hardiness zone 5a — a zone band wide enough that plant choice, not possibility, is the interesting question.
A short list that earns its place here — cabbage, cranberry, lavender, and collard greens — with any one site's soil, sun, and drainage making the final cut.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Sioux County holds more than one microclimate.
Soils and elevations shift across Sioux County, so your frost dates and drainage aren't the county average. 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 Sioux County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Sioux County — the short answer
Sioux County, Iowa: USDA zone 5a, about 179 days between hard freezes, across 491K acres.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 20
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 16
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~179
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 491K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 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 5a is Sioux County's average, not your lot's — a low corner or a tree line moves it. Against Sioux County's 179-day season, see what your own ground reads.
Heat in Sioux County
Across a year, Sioux County accumulates about 2,624 growing degree days above 50°F, about 120 fewer than the middle Iowa county — ahead of 35 of Iowa’s 99 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Sioux County
Across Sioux County, the ground is predominantly Mollisols, where Galva, Primghar, and Radford are the most extensive named soil series. The soil is generally well drained with a silty clay loam surface. Topsoil pH runs about 5.8–6.5, slightly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Mollisols
Drainage
Well drained
Prime farmland
74%
Hydric soils
10%
Soil still varies lot by lot — soil types explained.
How the ground varies across Sioux County
The USDA soil survey maps 65% of Sioux County as well drained — but another 34% drains differently: 21% somewhat poorly drained, 11% poorly drained.
Galva is the most extensive named soil at 23% of mapped acres, then Primghar (14%) and Radford (4%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Sioux County
Each reading below is measured for Sioux County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Sioux County are well drained, in hydrologic group C — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Sioux County runs about pH 5.8–6.5, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Season length
MeasuredSioux County runs about 179 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
MeasuredSioux County sits in USDA hardiness zone 5a.
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 Sioux County is in
Sioux County sits in the Western Corn Belt Plains — EPA Level III, inside the wider Great Plains. One consistent ecological setting across the whole county.
What Grows in Sioux County
We scored all 1,086 plants against Sioux County's own USDA zone 5a and its own 179-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Iowa profile.
Is it too late to plant in Sioux County?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Mar 23; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 20 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 16 — long-season crops need about 90 days of runway, quick greens only 30. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
Documented around Sioux County
- monarch butterfly145 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Sioux County
USGS estimates 277,361 lb of Glyphosate on Sioux County farmland in 2019, its largest by weight, ahead of Acetochlor (181,430 lb) and Atrazine (85,498 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Sioux County — and how to grow with it.
We checked the federal record across Sioux County — 421 documented sites across 7 of the 9 source types we track.
The most significant on record: 3 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
There's a meaningful federal record across Sioux County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Sioux County
Closest first, across Sioux County. Listing isn't leaking, and distance isn't exposure.
- VER HOEF CHEV INCUnderground Storage Tanks · 600 ft
- VER HOEF AUTOMOTIVE INCBrownfields · 650 ft
- B & B SALVAGEBrownfields · 700 ft
- 095N45W12BBAA Sioux CenterNitrate · 750 ft
- SOO LUMBER CO INCUnderground Storage Tanks · 800 ft
- WHITE OAK STATION 58Underground Storage Tanks · 850 ft
- CASEYS GENERAL STORE 2431Underground Storage Tanks · 950 ft
- FORMER DOORNINK OIL COMPANYUnderground Storage Tanks · 950 ft
- CITY OF SIOUX CENTERUnderground Storage Tanks · 1000 ft
- FARMERS COOP SOCIETYUnderground Storage Tanks · 1200 ft
- VALSPARBrownfields · 1400 ft
- 095N45W05ADA 01892 1944Nitrate · 1400 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Sioux County'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 Sioux County.
Severity Distribution
across Sioux County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Sioux County, two things run higher than the national average across Sioux County — CAFO (9 sites) and PFAS (6 sites). That's not a problem with your land — it's information about it.
CAFO: CAFOs pose a different contamination profile than chemical sources.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Check your specific parcel in Sioux County
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 Sioux County average
Your land is one point inside Sioux County
Everything above resolves to Sioux County as a whole — one PHZM band and one county frost record, read across 491K 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 county 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 county average.
Your Lot vs the Sioux County Average
Sioux County Average
- ●USDA Zones 5a, averaged across Sioux County
- ●One soil character for all of Sioux County
- ●Frost dates read at Sioux County's scale: Apr 20 to Oct 16
YOUR Parcel
- ✓Your exact zone, not Sioux County's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Sioux County
Pull a site-specific report for your exact address in Sioux County, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Sioux County averages can't show:
We read public map data around Sioux County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Sioux County average
How we know this about Sioux County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Sioux County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Sioux County
When does frost risk typically end in Sioux County?
The last hard freeze (28°F) in Sioux County typically lands around Apr 20, 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 11.
How long is the growing season in Sioux County?
Measured between 28°F hard freezes, Sioux County sees about 179 frost-free days — roughly Apr 20 through Oct 16, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 11 to Oct 2, about 144 days.
Is the soil safe to grow vegetables in Sioux County?
The federal record around Sioux County is a meaningful one — 421 documented sites, mostly Nitrate entries (162), the nearest Underground Storage Tanks record about 0.1 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
Everything above is measured at Sioux County's scale — its 5a band and its 179-day season. Your yard writes its own version of Sioux County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Iowa's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Sioux County’s own scale
9 of the readings below were taken at Sioux County's own scale — its own ~179-day span between 28°F freezes, the 3 most extensive soil series mapped here and 421 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Sioux County's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Sioux County's own 28°F hard-freeze dates and its ~179-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Sioux CountyUSDA NRCS SSURGO
- 421 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.1 miles outFederal environmental registers
- Sioux County's boundary and the 491,463 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~179-day seasonGrowable Ground crop-matching engine
- Sioux County sitting wholly inside the Western Corn Belt PlainsUS EPA Level III Ecoregions
- Open occurrence records documented in Sioux County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Sioux County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Iowa grower plans around — written at state scale, so they stay on the state guidefrom Iowa
What this page can’t tell you
- How the season shifts across Sioux County — the ~179 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Sioux County's 491,463 acreswhy one lot differs from the next →
- Which of those 421 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Sioux Countyread your own land →