Mount Vernon, Iowa, sits in USDA hardiness zone 5a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
The conditions favor cabbage, cranberry, lavender, and collard greens, among others — though every individual site edits that list with its own soil, sun, and drainage.
Even in Mount Vernon, 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 Mount Vernon 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 Mount Vernon — soil, climate, flood, and parcel records. How we handle your address.
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Mount Vernon — the short answer
Mount Vernon, Iowa: USDA zone 5a, about 190 days between hard freezes, across 2K acres of city.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 13
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 20
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~190
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 2K 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 5a is Mount Vernon's average, not your lot's — a low corner or a tree line moves it. Against Mount Vernon's 190-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Mount Vernon
Each reading below is measured for Mount Vernon itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredMount Vernon runs about 190 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
MeasuredMount Vernon sits in USDA hardiness zone 5a.
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 Mount Vernon is in
Mount Vernon sits in the Western Corn Belt Plains — EPA Level III, inside the wider Great Plains. That is read at Mount Vernon's own centroid rather than borrowed from Linn County.
What Grows in Mount Vernon
Every plant below cleared Mount Vernon's own zone 5a and its 190-day season. Each card opens that plant's Iowa profile. How we score.
Is it too late to plant in Mount Vernon?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 16; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 13 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 20 — 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 Mount Vernon
Closest first, within ~10 miles of Mount Vernon. Listing isn't leaking, and distance isn't exposure.
- 082N05W10CBC 09254 1957Mount Vernon 3Nitrate · 500 ft
- CORNELL COLLEGEBrownfields · 650 ft
- MAINTENANCE BLDGUnderground Storage Tanks · 850 ft
- BUS BARNUnderground Storage Tanks · 1100 ft
- DAMAN BROS 66Underground Storage Tanks · 1500 ft
- 082N05W10CBAA 23181 1972Mount Vernon 5Nitrate · 1600 ft
- 082N05W10CBAA 1936Mount Vernon 2Nitrate · 1600 ft
- GUPPYS ON THE GOUnderground Storage Tanks · 1700 ft
- U S WESTUnderground Storage Tanks · 2200 ft
- LINN COUNTY ROAD DEPTUnderground Storage Tanks · 2300 ft
- HILLTOP CLEANERSBrownfields · 2600 ft
- JERRYS TRUE VALUE HARDWAREUnderground Storage Tanks · 0.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Mount Vernon'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 Mount Vernon.
Total Sites
224
within ~10 miles of Mount Vernon
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Mount Vernon
Severity Distribution
within ~10 miles of Mount Vernon
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Mount Vernon, Nitrate runs higher than the national average — 118 sites within ~10 miles of Mount Vernon. That's not a problem with your land — it's information about it.
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 Mount Vernon
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 Mount Vernon average
Your land is one point inside Mount Vernon
Everything above resolves to Mount Vernon as a whole — one PHZM band and one 28°F frost record, read across 2K 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 Mount Vernon Average
Mount Vernon Average
- ●USDA Zones 5a, averaged across Mount Vernon
- ●One soil character for all of Mount Vernon
- ●Frost dates read at Mount Vernon's scale: Apr 13 to Oct 20
YOUR Parcel
- ✓Your exact zone, not Mount Vernon's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Mount Vernon
Pull a site-specific report for your exact address in Mount Vernon, Iowa — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Mount Vernon averages can't show:
We read public map data around Mount Vernon — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Mount Vernon average
How we know this about Mount Vernon
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 Mount Vernon’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 Mount Vernon
When does frost risk typically end in Mount Vernon?
The last hard freeze (28°F) in Mount Vernon typically lands around Apr 13, 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 4.
When is the first frost in Mount Vernon?
The first hard freeze (28°F) in Mount Vernon typically arrives around Oct 20, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 6, so the watching starts about Sep 20 — about 190 days after the spring freeze cleared.
How long is the growing season in Mount Vernon?
Measured between 28°F hard freezes, Mount Vernon sees about 190 frost-free days — roughly Apr 13 through Oct 20, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 4 to Oct 6, about 155 days.
Is the soil safe to grow vegetables in Mount Vernon?
The federal record around Mount Vernon is a meaningful one — 224 documented sites, mostly Nitrate entries (118), the nearest Nitrate 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 Mount Vernon?
From about Sep 20 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 20 (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 20. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Mount Vernon's scale — its 5a band and its 190-day season. Your yard writes its own version of Mount Vernon'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 Mount Vernon’s own scale
6 of the readings below were taken at Mount Vernon's own scale — its own ~190-day season between 28°F freezes, the 2,390 acres it covers and 224 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Mount Vernon's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Mount Vernon's own 28°F hard-freeze dates, about Apr 13 and Oct 20 and the ~190-day span between themNOAA 1991–2020 Climate Normals
- 224 documented contamination sites on the federal record near Mount Vernon, the closest Nitrate record under a tenth of a mile out from the town centreFederal environmental registers
- Mount Vernon's boundary and the 2,390 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~190-day seasonGrowable Ground crop-matching engine
- The ecoregion at Mount Vernon'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 Mount Vernon's 2,390 acres read through its county's SSURGO summaryfrom Linn County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Linn 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 Linn County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Mount Vernon's 2,390 acreswhy one lot differs from the next →
- Which side of Mount Vernon you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 2,390 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate 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 Mount Vernon-wide figureread your own land →
More in Iowa
Wider growing context
What grows across IowaMount Vernon sits outside our named growing regions, so Iowa as a whole is its closest context here.
Nearby growing guides