Colwell, Iowa, sits in USDA hardiness zone 5a — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
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 Colwell, 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 Colwell 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 Colwell — soil, climate, flood, and parcel records. How we handle your address.
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Colwell — the short answer
Colwell, Iowa: USDA zone 5a, about 182 days between hard freezes, across 106 acres of city.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 18
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 17
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~182
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 106 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 Colwell's average, not your lot's — a low corner or a tree line moves it. Against Colwell's 182-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Colwell
Each reading below is measured for Colwell itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredColwell runs about 182 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
MeasuredColwell 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 Colwell is in
Colwell sits in the Western Corn Belt Plains — EPA Level III, inside the wider Great Plains. That is read at Colwell's own centroid rather than borrowed from Floyd County.
What Grows in Colwell
Every plant below cleared Colwell's own zone 5a and its 182-day season. Each card opens that plant's Iowa profile. How we score.
Is it too late to plant in Colwell?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 21; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 18 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 17 — 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.
What's on the federal record near Colwell
Closest first, within ~10 miles of Colwell. Listing isn't leaking, and distance isn't exposure.
- COLWELL COOPERATIVEUnderground Storage Tanks · 600 ft
- 096N15W11BBA 1968Colwell 1Nitrate · 1000 ft
- NOLAN COOK FARMBrownfields · 4.5 mi
- 096N14W33BCBNitrate · 5.9 mi
- PEMBINA COCHIN LLC - CHARLES CITY MAINTENANCE CENTERBrownfields · 6.1 mi
- CHARLES CITY WATER SUPPLYPFAS · 6.3 mi
- CEDAR VALLEY TRANSPORTATION CENTERUnderground Storage Tanks · 6.5 mi
- 095N16W01AAB 04869 1950Charles City 5Nitrate · 6.7 mi
- 095N16W01AAB 15317 1963Charles City 7Nitrate · 6.7 mi
- 095N15W06DBBD 22373 1970Nitrate · 6.7 mi
- WHITE FARM EQUIPMENT CO. DUMPSuperfund · 6.7 mi
- 095N15W06BDDA 00814 1939Charles City 4Nitrate · 6.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Colwell'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 Colwell.
Sources Checked
within ~10 miles of Colwell
Severity Distribution
within ~10 miles of Colwell
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Colwell, two things run higher than the national average within ~10 miles of Colwell — Superfund (3 sites) and Nitrate (40 sites). That's not a problem with your land — it's information about it.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Colwell
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 Colwell average
Your land is one point inside Colwell
Everything above resolves to Colwell as a whole — one PHZM band and one 28°F frost record, read across 106 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 Colwell Average
Colwell Average
- ●USDA Zones 5a, averaged across Colwell
- ●One soil character for all of Colwell
- ●Frost dates read at Colwell's scale: Apr 18 to Oct 17
YOUR Parcel
- ✓Your exact zone, not Colwell's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Colwell
Pull a site-specific report for your exact address in Colwell, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Colwell averages can't show:
We read public map data around Colwell — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Colwell average
How we know this about Colwell
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 Colwell’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 Colwell
When does frost risk typically end in Colwell?
The last hard freeze (28°F) in Colwell typically lands around Apr 18, 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 9.
When is the first frost in Colwell?
The first hard freeze (28°F) in Colwell typically arrives around Oct 17, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 3, so the watching starts about Sep 17 — about 182 days after the spring freeze cleared.
How long is the growing season in Colwell?
Measured between 28°F hard freezes, Colwell sees about 182 frost-free days — roughly Apr 18 through Oct 17, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 9 to Oct 3, about 147 days.
Is the soil safe to grow vegetables in Colwell?
The federal record around Colwell runs heavier than most — 143 documented sites, mostly Underground Storage Tanks entries (70), the nearest Underground Storage Tanks record about 0.1 miles out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
How do I protect my plants from frost in Colwell?
From about Sep 17 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 17 (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 17. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Colwell's scale — its 5a band and its 182-day season. Your yard writes its own version of Colwell'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 Colwell’s own scale
6 of the readings below were taken at Colwell's own scale — its own ~182-day season between 28°F freezes, the 106 acres it covers and 143 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Colwell's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Colwell's own 28°F hard-freeze dates, about Apr 18 and Oct 17 and the ~182-day span between themNOAA 1991–2020 Climate Normals
- 143 documented contamination sites on the federal record near Colwell, the closest Underground Storage Tanks record about 0.1 miles out from the town centreFederal environmental registers
- Colwell's boundary and the 106 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~182-day seasonGrowable Ground crop-matching engine
- The ecoregion at Colwell'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 Colwell's 106 acres read through its county's SSURGO summaryfrom Floyd County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Floyd 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 Floyd County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Colwell's 106 acreswhy one lot differs from the next →
- Which side of Colwell you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 106 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.1 miles 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 Colwell-wide figureread your own land →
More in Iowa
Wider growing context
What grows across IowaColwell sits outside our named growing regions, so Iowa as a whole is its closest context here.
Nearby growing guides