Polk County, in Iowa, sits in USDA hardiness zone 5b — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Crops well matched to these conditions include cabbage, cranberry, lavender, and collard greens — though what thrives on any one site still turns on its specific soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Polk County holds more than one microclimate.
Soils and elevations shift across Polk 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 Polk County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Polk County — the short answer
Polk County, Iowa: USDA zone 5b, about 195 days between hard freezes, across 367K acres.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 11
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 23
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~195
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 367K 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 5b is Polk County's average, not your lot's — a low corner or a tree line moves it. Against Polk County's 195-day season, see what your own ground reads.
Heat in Polk County
Across a year, Polk County accumulates about 2,964 growing degree days above 50°F, about 220 more than the middle Iowa county — ahead of 73 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 Polk County
Across Polk County, the ground is predominantly Mollisols, where Clarion, Webster, and Nicollet are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.2–6.6, slightly acidic. Rainfall drains through hydrologic group B soils.
Soil order
Mollisols
Drainage
Well drained
Prime farmland
34%
Hydric soils
29%
Soil still varies lot by lot — soil types explained.
How the ground varies across Polk County
The USDA soil survey maps 39% of Polk County as well drained — but another 51% drains differently: 25% poorly drained, 15% somewhat poorly drained.
Clarion is the most extensive named soil at 21% of mapped acres, then Webster (10%) and Nicollet (9%).
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 Polk County
Each reading below is measured for Polk 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 Polk County are well drained, in hydrologic group B — 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 Polk County runs about pH 6.2–6.6, 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
Wet ground
MeasuredAbout 29% of Polk County is mapped as hydric — wetland — soil.
If your lot falls in one of those pockets, a standard in-ground bed will fight waterlogging all season, and roots that need air will struggle.
Check how your own ground drains before you dig; raised beds or moisture-loving plantings turn a wet corner from a problem into a niche.
USDA NRCS SSURGO
Season length
MeasuredPolk County runs about 195 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
The kind of country Polk County is in
Polk 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 Polk County
We scored all 1,086 plants against Polk County's own USDA zone 5b and its own 195-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 Polk County?
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 14; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 11 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 23 — 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.
Documented around Polk County
- Japanese beetle2 documented records
- monarch butterfly2,334 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Polk County
USGS estimates 140,229 lb of Glyphosate on Polk County farmland in 2019, its largest by weight, ahead of Acetochlor (71,976 lb) and Atrazine (47,988 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 Polk County — and how to grow with it.
We checked the federal record across Polk County — 1,963 documented sites across 7 of the 9 source types we track.
The most significant on record: 18 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Polk County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Polk County
Closest first, across Polk County. Listing isn't leaking, and distance isn't exposure.
- AMAZON.COM SERVICES LLC - SIA2Brownfields · 0.6 mi
- OLD DOMINION FREIGHT LINESUnderground Storage Tanks · 0.6 mi
- GXO WAREHOUSE COMPANY INCBrownfields · 0.7 mi
- EXECUTIVE 1 AVIATION, INCBrownfields · 0.7 mi
- SAMS CLUB #6979Underground Storage Tanks · 0.7 mi
- REVERE PLASTICS SYSTEMS, LLCBrownfields · 0.7 mi
- SAMS CLUB 6979Brownfields · 0.7 mi
- CARQUEST DIST CENTERBrownfields · 0.7 mi
- MILLS FLEET FARMBrownfields · 0.8 mi
- BAYER RESEARCH AND DEVELOPMENT SERVICES LLCBrownfields · 0.9 mi
- XPEDXBrownfields · 0.9 mi
- CASEY''S GENERAL STORE 90Underground Storage Tanks · 1.1 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Polk 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 Polk County.
Sources Checked
across Polk County
Severity Distribution
across Polk County
Highest-Severity Sites
Know Before You Grow
- •Underground tanks leak petroleum as they age — near a former filling station, test the soil.
- •Near a brownfield, raised beds of imported soil give your food clean ground.
- •TRI facilities report what they release. Check the wind — downwind beds catch more of it.
Check your specific parcel in Polk 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 Polk County average
Your land is one point inside Polk County
Everything above resolves to Polk County as a whole — one PHZM band and one county frost record, read across 367K 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 Polk County Average
Polk County Average
- ●USDA Zones 5b, averaged across Polk County
- ●One soil character for all of Polk County
- ●Frost dates read at Polk County's scale: Apr 11 to Oct 23
YOUR Parcel
- ✓Your exact zone, not Polk County's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Polk County
Pull a site-specific report for your exact address in Polk County, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Polk County averages can't show:
We read public map data around Polk County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Polk County average
How we know this about Polk 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 Polk County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Polk County
When does frost risk typically end in Polk County?
The last hard freeze (28°F) in Polk County typically lands around Apr 11, 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 2.
How long is the growing season in Polk County?
Measured between 28°F hard freezes, Polk County sees about 195 frost-free days — roughly Apr 11 through Oct 23, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 2 to Oct 9, about 160 days.
Is the soil safe to grow vegetables in Polk County?
The federal record around Polk County runs heavier than most — 1,963 documented sites, mostly Underground Storage Tanks entries (1,096), the nearest Brownfields record about 0.6 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.
Everything above is measured at Polk County's scale — its 5b band and its 195-day season. Your yard writes its own version of Polk 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 Polk County’s own scale
9 of the readings below were taken at Polk County's own scale — its own ~195-day span between 28°F freezes, the 3 most extensive soil series mapped here and 1,963 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Polk County's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Polk County's own 28°F hard-freeze dates and its ~195-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Polk CountyUSDA NRCS SSURGO
- 1,963 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 0.6 miles outFederal environmental registers
- Polk County's boundary and the 366,540 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~195-day seasonGrowable Ground crop-matching engine
- Polk County sitting wholly inside the Western Corn Belt PlainsUS EPA Level III Ecoregions
- Open occurrence records documented in Polk County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Polk 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 Polk County — the ~195 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 Polk County's 366,540 acreswhy one lot differs from the next →
- Which of those 1,963 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 Polk Countyread your own land →