The Loess Hills spans USDA hardiness zones 5a-5b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Western Iowa's Loess Hills are a narrow ridge of wind-blown silt piled up to roughly 200 feet deep along the Missouri River — among the deepest loess deposits on Earth, rivaled only by China's Loess Plateau. That soil grows differently from the rest of Iowa: it drains fast, warms early in spring, and leaves ridgetops droughty while eroding hard on steep south- and west-facing slopes. It's distinctive enough that the TTB drew the Loess Hills District wine region across it in 2016 (27 CFR § 9.255), and cold-hardy grapes now share the slopes with orchards, dry prairie remnants, and terraced market gardens. These seven river-edge counties run zone 5a in the north to 5b in the south, roughly a 180–205 day season — so the calendar below is your honest western-Iowa county window, and the growing notes lean into what loess actually asks of you: cover the slopes, watch the drought on the ridges, and let the fast drainage work for your earliest crops. Growers here do well with sweet corn, tomato, apple, and hosta — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
The Loess Hills spans Iowa.
Your yard isn't all of the Loess Hills.
The Loess Hills spans USDA zones 5a-5b, but your parcel sits in exactly one — and slope, tree cover, and low spots nudge it further. 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 Loess Hills — soil, climate, flood, and parcel records. How we handle your address.
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The Loess Hills — the short answer
The Loess Hills: USDA zones 5a-5b, 180–204 frost-free days, in Iowa.
- USDA zones
- 5a-5b
- USDA PHZM 2023, aggregated over the footprint
- Frost-free season
- 180–204 days
- NOAA Regional Climate Centers ACIS, 1991-2020
- Counties
- 7
- US Census TIGER/Line 2025
- Region type
- County cluster
- Growable Ground growing-region registry
Region boundary: Growable Ground growing-region registry — curated county clusters, EPA Level III ecoregions, and town clusters drawn finer than any county. Where a region publishes no measured season, no season figure is shown.
Hardiness Zone Range
What Grows in the Loess Hills
Plants matched to the Loess Hills' USDA zones 5a-5b, ordered by how much hardiness margin each has across the region — the ones with room to spare at both ends of this band lead. Each links to its full growing profile.
Native Plants of the Loess Hills
Plants the USDA PLANTS Database documents as native and present in this region’s state, kept only where the published hardiness range meets the Loess Hills’s USDA zones 5a-5b — closest range match first. Presence is recorded by state, so a plant can be documented across the state and still be scarce in your corner of the region.
The ground across the Loess Hills
The USDA soil survey maps this ground county by county. These are those records weighted by land area across seven member counties — this region’s own profile, not a state figure.
The ground is predominantly Mollisols, at 45% of mapped acres, followed by Entisols (32%), Inceptisols (19%) and Vertisols (3%). Six soil orders appear somewhere inside the footprint, which is the honest reason a regional soil answer only goes so far. The most extensive named soils are Ida, Napier, and Galva.
66% of those acres are well drained, and another 12% poorly drained, 11% somewhat poorly drained. Topsoil pH runs 5.7–7.7 between the lowest and the highest county on record. 34% of the footprint is classed prime farmland.
Soil order
Mollisols
Drainage
Well drained
Topsoil pH
5.7–7.7
Hydric soils
14%
Soil changes across a driveway, so which of these your own ground sits on is a parcel question rather than a regional one. Monona County holds the most wetland ground here, at 30% — soil types explained.
USDA NRCS SSURGO via Soil Data Access
What this means for growing in the Loess Hills
The soil survey reads this ground county by county, and the readings above are those records summed across the Loess Hills. Here is what they mean for a garden here — and the move an experienced grower makes about each one.
Drainage
From county records66% of the mapped acres across the Loess Hills are well drained — ground that drains quickly. That is area-weighted across all seven of its mapped counties.
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
From county recordsTopsoil across the Loess Hills runs pH 5.7–7.7 — near neutral in all seven of them.
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
Safe to Grow Here?
What the federal record shows across the Loess Hills — and how to grow with it.
Across the Loess Hills' 7 counties the federal record holds 2,176 documented sites, mostly Underground Storage Tanks (1,179), Nitrate (444) and Brownfields (413). The heaviest single county is Woodbury County, with 763.
That is a regional count, not a reading of any one lot — proximity to a documented site is information, not a diagnosis. Open the map outlined to the Loess Hills to see which records sit where you actually grow.
Sources Checked
Summed across the 7 counties in the Loess Hills
Know Before You Grow
- •Underground tanks leak petroleum as they age — near a former filling station, test the soil.
- •On a private well, test for nitrates: above 10 mg/L the water needs treatment before irrigating.
- •Near a brownfield, raised beds of imported soil give your food clean ground.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Your land is one point inside the Loess Hills
Everything above resolves to the Loess Hills as a whole — a footprint spanning USDA zones 5a-5b. Your parcel sits in exactly one of them. 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 region 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 regional average.
Your Lot vs the Loess Hills Average
Loess Hills Average
- ●USDA Zones 5a-5b, averaged across Loess Hills
- ●One soil character for all of Loess Hills
- ●State-average frost dates
YOUR Parcel
- ✓Your exact zone, not Loess Hills' 5a-5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in the Loess Hills
Pull a site-specific report for your exact address in the Loess Hills — soil, sun, drainage, frost risk, contamination, and scored plant recommendations.
Three things about your lot that Loess Hills averages can't show:
We read public map data around The Loess Hills — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Loess Hills average
How we know this about the Loess Hills
The boundary: a cluster of neighboring counties. Growing regions have no official boundary, so this footprint is our published one, and every figure on this page was measured over the counties inside it rather than borrowed from the state around it.
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, aggregated across the footprint; the growing season from NOAA Regional Climate Centers ACIS 1991–2020 28°F normals, read at each member’s own record; boundaries from US Census TIGER/Line 2025; the contamination record from the federal sources named in that beat above; the soil from the USDA NRCS SSURGO survey, read at each member county’s own record and weighted to this footprint by land area. Where a member carries no record of its own, it is absent from the figure rather than filled in.
Common questions about the Loess Hills
What hardiness zone is the Loess Hills?
The Loess Hills spans USDA hardiness zones 5a-5b, aggregated from the USDA Agricultural Research Service Plant Hardiness Zone Map 2023 across the region's counties. Zones reflect average annual extreme minimum temperatures from 1991–2020 data.
How long is the growing season in the Loess Hills?
Measured between 28°F hard freezes, the Loess Hills' counties mostly run 185 to 202 frost-free days, median 190 (NOAA Regional Climate Centers ACIS, 1991–2020, over 7 member counties). That 17-day spread is the honest read — no single season describes 7 counties, and each county guide below carries its own.
When does frost risk end in the Loess Hills?
Across the Loess Hills, the middle half of member counties see their last 28°F hard freeze between Apr 7 and Apr 16 (median Apr 13), and their first fall freeze between Oct 18 and Oct 26. Those are hard freezes, not the last light frost: tender transplants wait for about May 4, and elevation decides which end of a 9-day spread you garden in.
What grows well in the Loess Hills?
The Loess Hills' conditions suit plants such as Sweet Corn, Tomato, Apple, Hosta. What actually thrives on any one site still turns on its specific soil, sun, and drainage — we score each plant against the real conditions at your address.
How is the Loess Hills defined?
The Loess Hills is defined here as a curated cluster of 7 neighboring counties that share a growing character. Growing regions have no official boundary, so this footprint is our published one — every county in it is named on this page.
Which states does the Loess Hills cover?
The Loess Hills spans Iowa. Each state's full growing guide is linked on this page.
What other growing regions cover the same states?
Driftless Area and Southeast Iowa / Great River Region (Mississippi–Des Moines river corner) share at least one state with the Loess Hills. Growing regions overlap and interlock — a single address can sit inside more than one, which is why the precise read is always the parcel, not the region.
What this page reads at the Loess Hills’s own scale
6 of the readings below were taken at the Loess Hills' own scale — the zone 5a-5b band across its footprint, a median 190-day season across its 7 counties and 2,176 documented federal contamination records across its 7 counties, 763 of them in Woodbury County alone; one is borrowed from a wider read, named and linked below.
Measured here
- The USDA hardiness band 5a-5b aggregated across all 7 counties in the footprintUSDA PHZM 2023
- The boundary itself — the 7 counties this region is curated fromGrowable Ground subregion registry
- The growing character that makes this region distinct from the states it crossesGrowable Ground subregion registry
- The 28°F season across the footprint — the middle half of its 7 counties run 185 to 202 frost-free days, median 190NOAA Regional Climate Centers ACIS, 1991-2020
- The federal contamination record over the whole footprint — 2,176 documented federal contamination records across its 7 counties, 763 of them in Woodbury County aloneEPA, USGS and USDA federal site records
- The soil order mix across the footprint — 45% Mollisols, topsoil pH 5.7–7.7, area-weighted across its 7 mapped countiesUSDA NRCS SSURGO
Inherited from a wider read
- The candidate plant list — its state's curated sets, merged and filtered to zones 5a-5bfrom Iowa
What this page can’t tell you
- Which end of the 17-day range your ground sits at — 185 days at one extreme, 202 at the other, decided mostly by elevationfrost dates explained →
- Which of those soils your own ground sits on — the survey maps them county-wide, and they change across a drivewaysoil types explained →
- The soil pH, drainage, sun hours, and frost pockets on one specific lotwhy one lot differs from the next →
Explore the Loess Hills
State growing guides
Counties in this region
Other growing regions across Iowa
An unglaciated landscape of steep ridges, deep valleys, and spring-fed coulees in the Upper Midwest — a stronghold of diversified small farms and cold-hardy fruit.
Southeast Iowa's Mississippi–Des Moines river corner is the warm anchor of the state: Lee and Des Moines counties are Iowa's ONLY 6a ground, and the eight-county cluster runs 204–216 frost-free days — roughly 15–27 days past the Iowa median of 189 and up to 48 days longer than the coldest far-north counties (168). That extra window is the length of a real second planting: growers here can genuinely finish sweet potatoes, okra, and long-season melons, and overwinter peach and fig that struggle upstate. So this refines Iowa's 4b–6a state compromise calendar — which sits about three weeks short of Lee County's actual window — rather than restating it.