Johnston, Iowa, sits in USDA hardiness zone 5b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
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 Johnston, 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 Johnston 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 Johnston — soil, climate, flood, and parcel records. How we handle your address.
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Johnston — the short answer
Johnston, Iowa: USDA zone 5b, about 198 days between hard freezes, across 12K acres of city.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 8
- 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
- ~198
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 12K 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 Johnston's average, not your lot's — a low corner or a tree line moves it. Against Johnston's 198-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Johnston
Each reading below is measured for Johnston itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredJohnston runs about 198 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
MeasuredJohnston 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 Johnston is in
Johnston sits in the Western Corn Belt Plains — EPA Level III, inside the wider Great Plains. That is read at Johnston's own centroid rather than borrowed from Polk County.
What Grows in Johnston
Every plant below cleared Johnston's own zone 5b and its 198-day season. Each card opens that plant's Iowa profile. How we score.
Is it too late to plant in Johnston?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Mar 11; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 8 (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 Johnston
Closest first, within ~10 miles of Johnston. Listing isn't leaking, and distance isn't exposure.
- JOHNSTON MUNICIPAL WATER SUPPLYPFAS · 2000 ft
- PIONEER HI-BRED INTERNATIONAL INC - EMC BLDG/REID COMPLEXBrownfields · 0.5 mi
- CAMP DODGEToxics Release Inventory · 0.7 mi
- CAMP DODGEBrownfields · 0.7 mi
- PIONEER HI-BRED INTERNATIONAL INCUnderground Storage Tanks · 0.7 mi
- 079N25W03AA 02752 1946Nitrate · 0.8 mi
- 080N25W34DDC 02370 1946Nitrate · 0.9 mi
- 079N25W02CBB 00613 1937Nitrate · 1.0 mi
- CASEY''S GENERAL STORE 2816Underground Storage Tanks · 1.0 mi
- HYPERION FIELD CLUBUnderground Storage Tanks · 1.0 mi
- HYPERION FIELD CLUBBrownfields · 1.0 mi
- PIONEER HI-BRED INTERNATIONAL INC - BEAVER CREEK CAMPUSBrownfields · 1.4 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Johnston'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 Johnston.
Sources Checked
within ~10 miles of Johnston
Severity Distribution
within ~10 miles of Johnston
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 Johnston
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 Johnston average
Your land is one point inside Johnston
Everything above resolves to Johnston as a whole — one PHZM band and one 28°F frost record, read across 12K 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 Johnston Average
Johnston Average
- ●USDA Zones 5b, averaged across Johnston
- ●One soil character for all of Johnston
- ●Frost dates read at Johnston's scale: Apr 8 to Oct 23
YOUR Parcel
- ✓Your exact zone, not Johnston's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Johnston
Pull a site-specific report for your exact address in Johnston, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Johnston averages can't show:
We read public map data around Johnston — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Johnston average
How we know this about Johnston
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 Johnston’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 Johnston
When does frost risk typically end in Johnston?
The last hard freeze (28°F) in Johnston typically lands around Apr 8, 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 29.
When is the first frost in Johnston?
The first hard freeze (28°F) in Johnston 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 198 days after the spring freeze cleared.
How long is the growing season in Johnston?
Measured between 28°F hard freezes, Johnston sees about 198 frost-free days — roughly Apr 8 through Oct 23, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 29 to Oct 9, about 163 days.
Is the soil safe to grow vegetables in Johnston?
The federal record around Johnston runs heavier than most — 1,499 documented sites, mostly Underground Storage Tanks entries (836), the nearest PFAS record about 0.4 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.
How do I protect my plants from frost in Johnston?
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 Johnston's scale — its 5b band and its 198-day season. Your yard writes its own version of Johnston'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 Johnston’s own scale
6 of the readings below were taken at Johnston's own scale — its own ~198-day season between 28°F freezes, the 12,474 acres it covers and 1,499 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Johnston's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Johnston's own 28°F hard-freeze dates, about Apr 8 and Oct 23 and the ~198-day span between themNOAA 1991–2020 Climate Normals
- 1,499 documented contamination sites on the federal record near Johnston, the closest PFAS record about 0.4 miles out from the town centreFederal environmental registers
- Johnston's boundary and the 12,474 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~198-day seasonGrowable Ground crop-matching engine
- The ecoregion at Johnston's own centroid, the Western Corn Belt PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Johnston's 12,474 acres read through its county's SSURGO summaryfrom Polk County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Polk 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 Polk County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Johnston's 12,474 acreswhy one lot differs from the next →
- Which side of Johnston you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 12,474 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest PFAS record about 0.4 miles 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 Johnston-wide figureread your own land →
More in Iowa
Wider growing context
What grows across IowaJohnston sits outside our named growing regions, so Iowa as a whole is its closest context here.
Nearby growing guides