Mason City, Illinois, sits in USDA hardiness zone 6a — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Among the crops suited to this profile: cabbage, hazelnut, lavender, and collard greens. The site-level story — soil, sun, drainage — decides the rest.
Even in Mason City, 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 Mason City 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 Mason City — soil, climate, flood, and parcel records. How we handle your address.
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Mason City — the short answer
Mason City, Illinois: USDA zone 6a, about 209 days between hard freezes, across 648 acres of city.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 5
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 31
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~209
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 648 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 6a is Mason City's average, not your lot's — a low corner or a tree line moves it. Against Mason City's 209-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Mason City
Each reading below is measured for Mason City itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredMason City runs about 209 days between hard freezes — a long growing season.
There is slack for succession plantings and slow-finishing crops: many vegetables can be sown twice, and the heat-lovers have time to ripen fully.
Plan a second sowing of quick crops after the first comes out, and use the fall window most gardeners let sit idle.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredMason City sits in USDA hardiness zone 6a.
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 Mason City is in
Mason City sits in the Central Corn Belt Plains — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Mason City's own centroid rather than borrowed from Mason County.
What Grows in Mason City
Every plant below cleared Mason City's own zone 6a and its 209-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Mason City?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Mar 8; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 5 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 31 — long-season crops need about 90 days of runway, quick greens only 30. There is slack in a calendar like this — late plantings, second rounds of favorites, and a fall bench that keeps beds working.
What's on the federal record near Mason City
Closest first, within ~10 miles of Mason City. Listing isn't leaking, and distance isn't exposure.
- Mason City Green OilUnderground Storage Tanks · 200 ft
- L & G SerUnderground Storage Tanks · 250 ft
- BEST AUTOMOTIVE INCBrownfields · 250 ft
- City of Mason CityUnderground Storage Tanks · 300 ft
- Mason Co Ambulance BldgUnderground Storage Tanks · 300 ft
- Nelson JerryUnderground Storage Tanks · 300 ft
- Intermational Mineral & Chem CorpUnderground Storage Tanks · 300 ft
- At&T Teheran Radio TowerUnderground Storage Tanks · 300 ft
- Kaiser Ag Chemicals IncUnderground Storage Tanks · 300 ft
- Farmers Grain & Coal CoUnderground Storage Tanks · 300 ft
- Casey's General Store #1713Underground Storage Tanks · 300 ft
- WARECO 568Brownfields · 400 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Mason City'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 Mason City.
Total Sites
83
within ~10 miles of Mason City
Risk Level
Moderate
Highest-severity
1 Toxics Release Inventory facility
Sources Checked
within ~10 miles of Mason City
Severity Distribution
within ~10 miles of Mason City
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Mason City, Underground Storage Tanks runs higher than the national average — 53 sites within ~10 miles of Mason City. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Mason City
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 Mason City average
Your land is one point inside Mason City
Everything above resolves to Mason City as a whole — one PHZM band and one 28°F frost record, read across 648 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 Mason City Average
Mason City Average
- ●USDA Zones 6a, averaged across Mason City
- ●One soil character for all of Mason City
- ●Frost dates read at Mason City's scale: Apr 5 to Oct 31
YOUR Parcel
- ✓Your exact zone, not Mason City's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Mason City
Pull a site-specific report for your exact address in Mason City, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Mason City averages can't show:
We read public map data around Mason City — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Mason City average
How we know this about Mason City
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 Mason City’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 Mason City
When does frost risk typically end in Mason City?
The last hard freeze (28°F) in Mason City typically lands around Apr 5, 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 Apr 26.
When is the first frost in Mason City?
The first hard freeze (28°F) in Mason City typically arrives around Oct 31, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 17, so the watching starts about Oct 1 — about 209 days after the spring freeze cleared.
How long is the growing season in Mason City?
Measured between 28°F hard freezes, Mason City sees about 209 frost-free days — roughly Apr 5 through Oct 31, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 26 to Oct 17, about 174 days.
Is the soil safe to grow vegetables in Mason City?
The federal record around Mason City shows 83 documented sites, mostly Underground Storage Tanks entries (53), the nearest Underground Storage Tanks 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 Mason City?
From about Oct 1 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 31 (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 31. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Mason City's scale — its 6a band and its 209-day season. Your yard writes its own version of Mason City'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 Mason City’s own scale
6 of the readings below were taken at Mason City's own scale — its own ~209-day season between 28°F freezes, the 648 acres it covers and 83 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Mason City's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Mason City's own 28°F hard-freeze dates, about Apr 5 and Oct 31 and the ~209-day span between themNOAA 1991–2020 Climate Normals
- 83 documented contamination sites on the federal record near Mason City, the closest Underground Storage Tanks record under a tenth of a mile out from the town centreFederal environmental registers
- Mason City's boundary and the 648 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~209-day seasonGrowable Ground crop-matching engine
- The ecoregion at Mason City's own centroid, the Central Corn Belt PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Mason City's 648 acres read through its county's SSURGO summaryfrom Mason County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Mason County
- The growing challenges every Illinois grower plans around — written at state scale, so they stay on the state guidefrom Illinois
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Mason County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Mason City's 648 acreswhy one lot differs from the next →
- Which side of Mason City you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 648 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 Mason City-wide figureread your own land →
More in Illinois
Wider growing context
What grows across IllinoisMason City sits outside our named growing regions, so Illinois as a whole is its closest context here.
Nearby growing guides