Audubon County, in 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.
Well-matched crops include cabbage, cranberry, lavender, and collard greens, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Audubon County holds more than one microclimate.
Soils and elevations shift across Audubon 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 Audubon County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Audubon County — the short answer
Audubon County, Iowa: USDA zone 5a, about 183 days between hard freezes, across 283K acres.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 17
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 17
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~183
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 283K 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 Audubon County's average, not your lot's — a low corner or a tree line moves it. Against Audubon County's 183-day season, see what your own ground reads.
Heat in Audubon County
Across a year, Audubon County accumulates about 2,730 growing degree days above 50°F, about 14 fewer than the middle Iowa county — ahead of 47 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 Audubon County
Across Audubon County, the ground is predominantly Inceptisols, where Judson, Colo, and Ackmore are the most extensive named soil series. The soil is generally well drained with a silty clay loam surface. Topsoil pH runs about 5.9–6.3, slightly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Inceptisols
Drainage
Well drained
Prime farmland
16%
Hydric soils
13%
Soil still varies lot by lot — soil types explained.
How the ground varies across Audubon County
The USDA soil survey maps 68% of Audubon County as well drained — but another 31% drains differently: 24% poorly drained, 4% somewhat poorly drained.
Judson is the most extensive named soil at 10% of mapped acres, then Colo (9%) and Ackmore (7%).
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 Audubon County
Each reading below is measured for Audubon 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 Audubon 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 Audubon County runs about pH 5.9–6.3, 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
MeasuredAudubon County runs about 183 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
MeasuredAudubon 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 Audubon County is in
Audubon 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 Audubon County
We scored all 1,086 plants against Audubon County's own USDA zone 5a and its own 183-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 Audubon County?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Mar 20; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 17 (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.
Documented around Audubon County
- monarch butterfly1 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Audubon County
USGS estimates 231,513 lb of Glyphosate on Audubon County farmland in 2019, its largest by weight, ahead of Acetochlor (83,255 lb) and Metolachlor & Metolachlor-s (75,502 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 Audubon County — and how to grow with it.
We checked the federal record across Audubon County — 88 documented sites across 5 of the 9 source types we track.
The most significant on record: 4 Toxics Release Inventory facilities. Active industrial facilities reporting chemical releases to air, water, and land.
The federal record across Audubon County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Audubon County
Closest first, across Audubon County. Listing isn't leaking, and distance isn't exposure.
- 079N35W10CABB 26350 1981IGS & USGS WC-17Nitrate · 1.0 mi
- IDOT GARAGEUnderground Storage Tanks · 1.1 mi
- WORTHINGTON AG PARTS - AUDUBON DIVISIONBrownfields · 1.2 mi
- WASPYS TRUCK STOPUnderground Storage Tanks · 2.1 mi
- SOUTH SIDE WELDINGBrownfields · 2.2 mi
- IOWA NATIONAL GUARD ARMORYUnderground Storage Tanks · 2.4 mi
- AUDUBON COMMUNITY SCHOOL_Underground Storage Tanks · 2.7 mi
- MIDAMERICAN ENERGY COMPANY AUDUBON SERVICE CENTERBrownfields · 2.7 mi
- AUDUBON COOPUnderground Storage Tanks · 3.0 mi
- AUDUBON COUNTY SHEDUnderground Storage Tanks · 3.1 mi
- FARRIS SINCLAIR AND TIRESUnderground Storage Tanks · 3.1 mi
- CASEY''S GENERAL STORE 27Underground Storage Tanks · 3.2 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Audubon 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 Audubon County.
Total Sites
88
across Audubon County
Risk Level
Moderate
Highest-severity
4 Toxics Release Inventory facilities
Sources Checked
across Audubon County
Severity Distribution
across Audubon County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Audubon County, Nitrate runs higher than the national average — 34 sites across Audubon County. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
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 Audubon 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 Audubon County average
Your land is one point inside Audubon County
Everything above resolves to Audubon County as a whole — one PHZM band and one county frost record, read across 283K 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 Audubon County Average
Audubon County Average
- ●USDA Zones 5a, averaged across Audubon County
- ●One soil character for all of Audubon County
- ●Frost dates read at Audubon County's scale: Apr 17 to Oct 17
YOUR Parcel
- ✓Your exact zone, not Audubon County's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Audubon County
Pull a site-specific report for your exact address in Audubon County, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Audubon County averages can't show:
We read public map data around Audubon County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Audubon County average
How we know this about Audubon 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 Audubon County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Audubon County
When does frost risk typically end in Audubon County?
The last hard freeze (28°F) in Audubon County typically lands around Apr 17, 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 8.
How long is the growing season in Audubon County?
Measured between 28°F hard freezes, Audubon County sees about 183 frost-free days — roughly Apr 17 through Oct 17, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 8 to Oct 3, about 148 days.
Is the soil safe to grow vegetables in Audubon County?
The federal record around Audubon County shows 88 documented sites, mostly Underground Storage Tanks entries (40), the nearest Nitrate record about 1.0 miles 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.
Everything above is measured at Audubon County's scale — its 5a band and its 183-day season. Your yard writes its own version of Audubon 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 Audubon County’s own scale
9 of the readings below were taken at Audubon County's own scale — its own ~183-day span between 28°F freezes, the 3 most extensive soil series mapped here and 88 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Audubon County's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Audubon County's own 28°F hard-freeze dates and its ~183-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Audubon CountyUSDA NRCS SSURGO
- 88 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 1.0 miles outFederal environmental registers
- Audubon County's boundary and the 283,494 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~183-day seasonGrowable Ground crop-matching engine
- Audubon County sitting wholly inside the Western Corn Belt PlainsUS EPA Level III Ecoregions
- Open occurrence records documented in Audubon County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Audubon 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 Audubon County — the ~183 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 Audubon County's 283,494 acreswhy one lot differs from the next →
- Which of those 88 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 Audubon Countyread your own land →