Charter Oak, Iowa, sits in USDA hardiness zone 5a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
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.
Even in Charter Oak, 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 Charter Oak 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 Charter Oak — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Charter Oak — the short answer
Charter Oak, Iowa: USDA zone 5a, about 187 days between hard freezes, across 328 acres of city.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 14
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 18
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~187
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 328 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 Charter Oak's average, not your lot's — a low corner or a tree line moves it. Against Charter Oak's 187-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Charter Oak
Each reading below is measured for Charter Oak itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredCharter Oak runs about 187 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
MeasuredCharter Oak 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 Charter Oak is in
Charter Oak sits in the Western Corn Belt Plains — EPA Level III, inside the wider Great Plains. That is read at Charter Oak's own centroid rather than borrowed from Crawford County.
What Grows in Charter Oak
Every plant below cleared Charter Oak's own zone 5a and its 187-day season. Each card opens that plant's Iowa profile. How we score.
Is it too late to plant in Charter Oak?
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 17; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 14 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 18 — 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 Charter Oak
Closest first, within ~10 miles of Charter Oak. Listing isn't leaking, and distance isn't exposure.
- 084N41W23CCAD 1954Charter Oak Test 1Nitrate · 350 ft
- 084N41W23CCAD 05901 1953Charter Oak 4Nitrate · 450 ft
- CENTRAL TELEPHONE COMPANYUnderground Storage Tanks · 650 ft
- MIDAMERICAN ENERGY COMPANY CHARTER OAK SERVICE CENTERBrownfields · 750 ft
- CRAWFORD COUNTY ENGINEERS OFFICEUnderground Storage Tanks · 750 ft
- VOGT TRUCKINGUnderground Storage Tanks · 750 ft
- CHARTER OAK FEED & GRAIN INCUnderground Storage Tanks · 750 ft
- CMC REAL ESTATE CORPUnderground Storage Tanks · 750 ft
- CHARTER OAK-UTE JR-SR HIGH SCHOOLBrownfields · 900 ft
- R & L REPAIRBrownfields · 1100 ft
- 084N41W23CACC 1951Charter Oak 3Nitrate · 1100 ft
- 084N41W23CACB Charter OakNitrate · 1100 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Charter Oak'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 Charter Oak.
Total Sites
65
within ~10 miles of Charter Oak
Risk Level
Moderate
Highest-severity
4 Toxics Release Inventory facilities
Sources Checked
within ~10 miles of Charter Oak
Severity Distribution
within ~10 miles of Charter Oak
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Charter Oak, two things run higher than the national average within ~10 miles of Charter Oak — Nitrate (38 sites) and Toxics Release Inventory (4 sites). 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.
Toxics Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check prevailing wind direction — downwind parcels face higher exposure than upwind or crosswind locations.
Check your specific parcel in Charter Oak
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 Charter Oak average
Your land is one point inside Charter Oak
Everything above resolves to Charter Oak as a whole — one PHZM band and one 28°F frost record, read across 328 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 Charter Oak Average
Charter Oak Average
- ●USDA Zones 5a, averaged across Charter Oak
- ●One soil character for all of Charter Oak
- ●Frost dates read at Charter Oak's scale: Apr 14 to Oct 18
YOUR Parcel
- ✓Your exact zone, not Charter Oak's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Charter Oak
Pull a site-specific report for your exact address in Charter Oak, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Charter Oak averages can't show:
We read public map data around Charter Oak — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Charter Oak average
How we know this about Charter Oak
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 Charter Oak’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 Charter Oak
When does frost risk typically end in Charter Oak?
The last hard freeze (28°F) in Charter Oak typically lands around Apr 14, 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 5.
When is the first frost in Charter Oak?
The first hard freeze (28°F) in Charter Oak typically arrives around Oct 18, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 4, so the watching starts about Sep 18 — about 187 days after the spring freeze cleared.
How long is the growing season in Charter Oak?
Measured between 28°F hard freezes, Charter Oak sees about 187 frost-free days — roughly Apr 14 through Oct 18, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 5 to Oct 4, about 152 days.
Is the soil safe to grow vegetables in Charter Oak?
The federal record around Charter Oak shows 65 documented sites, mostly Nitrate entries (38), the nearest Nitrate 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 Charter Oak?
From about Sep 18 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 18 (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 18. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Charter Oak's scale — its 5a band and its 187-day season. Your yard writes its own version of Charter Oak'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 Charter Oak’s own scale
6 of the readings below were taken at Charter Oak's own scale — its own ~187-day season between 28°F freezes, the 328 acres it covers and 65 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Charter Oak's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Charter Oak's own 28°F hard-freeze dates, about Apr 14 and Oct 18 and the ~187-day span between themNOAA 1991–2020 Climate Normals
- 65 documented contamination sites on the federal record near Charter Oak, the closest Nitrate record under a tenth of a mile out from the town centreFederal environmental registers
- Charter Oak's boundary and the 328 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~187-day seasonGrowable Ground crop-matching engine
- The ecoregion at Charter Oak'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 Charter Oak's 328 acres read through its county's SSURGO summaryfrom Crawford County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Crawford 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 Crawford County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Charter Oak's 328 acreswhy one lot differs from the next →
- Which side of Charter Oak you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 328 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate 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 Charter Oak-wide figureread your own land →
More in Iowa
Wider growing context
What grows across IowaCharter Oak sits outside our named growing regions, so Iowa as a whole is its closest context here.