Williamson, Iowa, sits in USDA hardiness zone 5b — a zone band wide enough that plant choice, not possibility, is the interesting question.
These conditions suit cabbage, cranberry, lavender, and collard greens — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
Even in Williamson, 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 Williamson 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 Williamson — soil, climate, flood, and parcel records. How we handle your address.
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Williamson — the short answer
Williamson, Iowa: USDA zone 5b, about 194 days between hard freezes, across 244 acres of city.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 12
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 23
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~194
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 244 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 5b is Williamson's average, not your lot's — a low corner or a tree line moves it. Against Williamson's 194-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Williamson
Each reading below is measured for Williamson itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredWilliamson runs about 194 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
MeasuredWilliamson sits in USDA hardiness zone 5b.
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 Williamson is in
Williamson sits in the Central Irregular Plains — EPA Level III, inside the wider Great Plains. That is read at Williamson's own centroid rather than borrowed from Lucas County.
What Grows in Williamson
Every plant below cleared Williamson's own zone 5b and its 194-day season. Each card opens that plant's Iowa profile. How we score.
Is it too late to plant in Williamson?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 15; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 12 (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. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
What's on the federal record near Williamson
Closest first, within ~10 miles of Williamson. Listing isn't leaking, and distance isn't exposure.
- WILLIAMSON ELEMENTARY SCHOOLUnderground Storage Tanks · 100 ft
- LUCAS COUNTY ENGINEERUnderground Storage Tanks · 200 ft
- 073N21W36CCB 1908Nitrate · 1.7 mi
- 072N21W12ABBNitrate · 2.9 mi
- 073N20W30DDBNitrate · 3.0 mi
- 072N21W05CDD 1964Nitrate · 3.2 mi
- 073N20W30DDA 06242 1953Nitrate · 3.2 mi
- 072N20W06AACBNitrate · 3.3 mi
- ITC TRANSMISSION - MIDWEST LUCAS COUNTYBrownfields · 3.6 mi
- CHARITON MAINT GARAGEUnderground Storage Tanks · 3.6 mi
- 073N21W11ABB 19082 1966Nitrate · 4.0 mi
- 073N20W17CBC 09332 1956Nitrate · 4.1 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Williamson'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 Williamson.
Total Sites
208
within ~10 miles of Williamson
Risk Level
Elevated
Highest-severity
3 Toxics Release Inventory facilities
Sources Checked
within ~10 miles of Williamson
Severity Distribution
within ~10 miles of Williamson
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Williamson, Nitrate runs higher than the national average — 130 sites within ~10 miles of Williamson. 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.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Williamson
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 Williamson average
Your land is one point inside Williamson
Everything above resolves to Williamson as a whole — one PHZM band and one 28°F frost record, read across 244 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 Williamson Average
Williamson Average
- ●USDA Zones 5b, averaged across Williamson
- ●One soil character for all of Williamson
- ●Frost dates read at Williamson's scale: Apr 12 to Oct 23
YOUR Parcel
- ✓Your exact zone, not Williamson's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Williamson
Pull a site-specific report for your exact address in Williamson, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Williamson averages can't show:
We read public map data around Williamson — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Williamson average
How we know this about Williamson
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 Williamson’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 Williamson
When does frost risk typically end in Williamson?
The last hard freeze (28°F) in Williamson typically lands around Apr 12, 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 3.
When is the first frost in Williamson?
The first hard freeze (28°F) in Williamson typically arrives around Oct 23, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 9, so the watching starts about Sep 23 — about 194 days after the spring freeze cleared.
How long is the growing season in Williamson?
Measured between 28°F hard freezes, Williamson sees about 194 frost-free days — roughly Apr 12 through Oct 23, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 3 to Oct 9, about 159 days.
Is the soil safe to grow vegetables in Williamson?
The federal record around Williamson is a meaningful one — 208 documented sites, mostly Nitrate entries (130), the nearest Underground Storage Tanks record under a tenth of a mile out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do I protect my plants from frost in Williamson?
From about Sep 23 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 23 (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 23. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Williamson's scale — its 5b band and its 194-day season. Your yard writes its own version of Williamson'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 Williamson’s own scale
6 of the readings below were taken at Williamson's own scale — its own ~194-day season between 28°F freezes, the 244 acres it covers and 208 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Williamson's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Williamson's own 28°F hard-freeze dates, about Apr 12 and Oct 23 and the ~194-day span between themNOAA 1991–2020 Climate Normals
- 208 documented contamination sites on the federal record near Williamson, the closest Underground Storage Tanks record under a tenth of a mile out from the town centreFederal environmental registers
- Williamson's boundary and the 244 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~194-day seasonGrowable Ground crop-matching engine
- The ecoregion at Williamson's own centroid, the Central Irregular PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Williamson's 244 acres read through its county's SSURGO summaryfrom Lucas County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Lucas 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 Lucas County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Williamson's 244 acreswhy one lot differs from the next →
- Which side of Williamson you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 244 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks 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 Williamson-wide figureread your own land →
More in Iowa
Wider growing context
What grows across IowaWilliamson sits outside our named growing regions, so Iowa as a whole is its closest context here.
Nearby growing guides