Rockwell City, Iowa, sits in USDA hardiness zone 5a — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Reliable performers under these conditions include cabbage, cranberry, lavender, and collard greens; what your own ground favors still comes down to its soil, sun, and drainage.
Even in Rockwell City, 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 Rockwell City 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 Rockwell City — soil, climate, flood, and parcel records. How we handle your address.
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Rockwell City — the short answer
Rockwell City, Iowa: USDA zone 5a, about 189 days between hard freezes, across 3K acres of city.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 15
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 21
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~189
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 3K 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 5a is Rockwell City's average, not your lot's — a low corner or a tree line moves it. Against Rockwell City's 189-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Rockwell City
Each reading below is measured for Rockwell City itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredRockwell City runs about 189 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
MeasuredRockwell City 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 Rockwell City is in
Rockwell City sits in the Western Corn Belt Plains — EPA Level III, inside the wider Great Plains. That is read at Rockwell City's own centroid rather than borrowed from Calhoun County.
What Grows in Rockwell City
Every plant below cleared Rockwell City's own zone 5a and its 189-day season. Each card opens that plant's Iowa profile. How we score.
Is it too late to plant in Rockwell City?
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 18; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 15 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 21 — long-season crops need about 90 days of runway, quick greens only 30. Even past midsummer there is room for a true fall garden here, and garlic planted near the close carries the momentum into next year.
What's on the federal record near Rockwell City
Closest first, within ~10 miles of Rockwell City. Listing isn't leaking, and distance isn't exposure.
- ROCKWELL CITY JUNIOR HIGH SCHOOLUnderground Storage Tanks · 300 ft
- CASEY''S GENERAL STOREUnderground Storage Tanks · 700 ft
- THORNBURG OIL COMPANYUnderground Storage Tanks · 1100 ft
- 088N33W36ADAA 22007 1970Rockwell City 4Nitrate · 1200 ft
- ROBERT ONNENUnderground Storage Tanks · 1300 ft
- EMPLOYERS MUTUAL COSUnderground Storage Tanks · 1300 ft
- CALHOUN COUNTYUnderground Storage Tanks · 1300 ft
- STAR ENERGY FUEL 24 CARDTROLUnderground Storage Tanks · 1300 ft
- CMC REAL ESTATE CORPUnderground Storage Tanks · 1500 ft
- SPARKYS ONE STOPUnderground Storage Tanks · 1500 ft
- 088N33W36AADB 59068 2004Rockwell City 6Nitrate · 1500 ft
- 088N33W36ADB 04094 1950Rockwell City 3Nitrate · 1900 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Rockwell City'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 Rockwell City.
Total Sites
82
within ~10 miles of Rockwell City
Risk Level
Moderate
Highest-severity
1 Toxics Release Inventory facility
Sources Checked
within ~10 miles of Rockwell City
Severity Distribution
within ~10 miles of Rockwell City
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Rockwell City, Nitrate runs higher than the national average — 22 sites within ~10 miles of Rockwell City. 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 Rockwell City
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 Rockwell City average
Your land is one point inside Rockwell City
Everything above resolves to Rockwell City as a whole — one PHZM band and one 28°F frost record, read across 3K 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 Rockwell City Average
Rockwell City Average
- ●USDA Zones 5a, averaged across Rockwell City
- ●One soil character for all of Rockwell City
- ●Frost dates read at Rockwell City's scale: Apr 15 to Oct 21
YOUR Parcel
- ✓Your exact zone, not Rockwell City's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Rockwell City
Pull a site-specific report for your exact address in Rockwell City, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Rockwell City averages can't show:
We read public map data around Rockwell City — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Rockwell City average
How we know this about Rockwell City
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 Rockwell City’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 Rockwell City
When does frost risk typically end in Rockwell City?
The last hard freeze (28°F) in Rockwell City typically lands around Apr 15, 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 6.
When is the first frost in Rockwell City?
The first hard freeze (28°F) in Rockwell City typically arrives around Oct 21, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 7, so the watching starts about Sep 21 — about 189 days after the spring freeze cleared.
How long is the growing season in Rockwell City?
Measured between 28°F hard freezes, Rockwell City sees about 189 frost-free days — roughly Apr 15 through Oct 21, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 6 to Oct 7, about 154 days.
Is the soil safe to grow vegetables in Rockwell City?
The federal record around Rockwell City shows 82 documented sites, mostly Underground Storage Tanks entries (42), the nearest Underground Storage Tanks 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 Rockwell City?
From about Sep 21 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 21 (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 21. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Rockwell City's scale — its 5a band and its 189-day season. Your yard writes its own version of Rockwell City'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 Rockwell City’s own scale
6 of the readings below were taken at Rockwell City's own scale — its own ~189-day season between 28°F freezes, the 2,696 acres it covers and 82 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Rockwell City's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Rockwell City's own 28°F hard-freeze dates, about Apr 15 and Oct 21 and the ~189-day span between themNOAA 1991–2020 Climate Normals
- 82 documented contamination sites on the federal record near Rockwell City, the closest Underground Storage Tanks record under a tenth of a mile out from the town centreFederal environmental registers
- Rockwell City's boundary and the 2,696 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~189-day seasonGrowable Ground crop-matching engine
- The ecoregion at Rockwell City's own centroid, the Western Corn Belt PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Rockwell City's 2,696 acres read through its county's SSURGO summaryfrom Calhoun County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Calhoun County
- The growing challenges every Iowa grower plans around — written at state scale, so they stay on the state guidefrom Iowa
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Calhoun County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Rockwell City's 2,696 acreswhy one lot differs from the next →
- Which side of Rockwell City you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 2,696 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks 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 Rockwell City-wide figureread your own land →
More in Iowa
Wider growing context
What grows across IowaRockwell City sits outside our named growing regions, so Iowa as a whole is its closest context here.
Nearby growing guides