St. Charles, Idaho, sits in USDA hardiness zone 5a — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
On paper, cabbage, cranberry, lavender, and collard greens all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Even in St. Charles, 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 St. Charles 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 St. Charles — soil, climate, flood, and parcel records. How we handle your address.
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St. Charles — the short answer
St. Charles, Idaho: USDA zone 5a, about 149 days between hard freezes, across 469 acres of city.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 6
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 2
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~149
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 469 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 St. Charles's average, not your lot's — a low corner or a tree line moves it. Against St. Charles's 149-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in St. Charles
Each reading below is measured for St. Charles itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredSt. Charles runs about 149 days between hard freezes — a short growing season.
Long-maturing crops like melons, sweet potatoes, and winter squash can run out of runway before the first hard freeze, ripening late or not at all.
Lead with fast-maturing varieties, and stretch the season on both ends with cold frames, low tunnels, or a greenhouse.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredSt. Charles 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 St. Charles is in
St. Charles sits in the Wyoming Basin — EPA Level III, inside the wider North American Deserts. That is read at St. Charles's own centroid rather than borrowed from Bear Lake County.
What Grows in St. Charles
Every plant below cleared St. Charles's own zone 5a and its 149-day season. Each card opens that plant's Idaho profile. How we score.
Is it too late to plant in St. Charles?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Apr 8; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 6 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 2 — long-season crops need about 90 days of runway, quick greens only 30. Short seasons reward decisiveness — quick-maturing varieties late, hardy greens under cover, and next year’s garlic in the ground before it closes.
What's on the federal record near St. Charles
Closest first, within ~10 miles of St. Charles. Listing isn't leaking, and distance isn't exposure.
- LIFTON PLANTUnderground Storage Tanks · 2.5 mi
- 15S 43E 02AAC1Nitrate · 2.6 mi
- Blackstone MineMining · 2.9 mi
- Idaho Gem GroupMining · 3.2 mi
- 16S 43E 02DDB1Nitrate · 3.5 mi
- Worm Creek ProspectMining · 3.5 mi
- CONSOLIDATED MINESuperfund · 3.8 mi
- 14S 43E 35BBA1Nitrate · 3.9 mi
- Clark MineMining · 4.0 mi
- IZATT SERVICEUnderground Storage Tanks · 5.1 mi
- Bear Bottom Country StoreUnderground Storage Tanks · 5.2 mi
- KAREL S THOMASUnderground Storage Tanks · 5.2 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from St. Charles'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 St. Charles.
Total Sites
38
within ~10 miles of St. Charles
Risk Level
Elevated
Highest-severity
2 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of St. Charles
Severity Distribution
within ~10 miles of St. Charles
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around St. Charles, two things run higher than the national average within ~10 miles of St. Charles — Mining (7 sites) and Nitrate (20 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in St. Charles
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 St. Charles average
Your land is one point inside St. Charles
Everything above resolves to St. Charles as a whole — one PHZM band and one 28°F frost record, read across 469 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 St. Charles Average
St. Charles Average
- ●USDA Zones 5a, averaged across St. Charles
- ●One soil character for all of St. Charles
- ●Frost dates read at St. Charles's scale: May 6 to Oct 2
YOUR Parcel
- ✓Your exact zone, not St. Charles's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in St. Charles
Pull a site-specific report for your exact address in St. Charles, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that St. Charles averages can't show:
We read public map data around St. Charles — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the St. Charles average
How we know this about St. Charles
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 St. Charles’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 St. Charles
When does frost risk typically end in St. Charles?
The last hard freeze (28°F) in St. Charles typically lands around May 6, 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 27.
When is the first frost in St. Charles?
The first hard freeze (28°F) in St. Charles typically arrives around Oct 2, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 18, so the watching starts about Sep 2 — about 149 days after the spring freeze cleared.
How long is the growing season in St. Charles?
Measured between 28°F hard freezes, St. Charles sees about 149 frost-free days — roughly May 6 through Oct 2, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 27 to Sep 18, about 114 days.
Is the soil safe to grow vegetables in St. Charles?
The federal record around St. Charles is a meaningful one — 38 documented sites, mostly Nitrate entries (20), the nearest Underground Storage Tanks record about 2.5 miles 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 gardeners stretch the season in St. Charles?
With about 149 frost-free days between hard freezes, St. Charles rewards the classic extension moves: floating row cover buys roughly two to four extra weeks at each shoulder — on this season that is a working window nearer 177 to 205 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 6 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at St. Charles's scale — its 5a band and its 149-day season. Your yard writes its own version of St. Charles'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 St. Charles’s own scale
6 of the readings below were taken at St. Charles's own scale — its own ~149-day season between 28°F freezes, the 469 acres it covers and 38 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- St. Charles's own USDA hardiness band, zones 5aUSDA PHZM 2023
- St. Charles's own 28°F hard-freeze dates, about May 6 and Oct 2 and the ~149-day span between themNOAA 1991–2020 Climate Normals
- 38 documented contamination sites on the federal record near St. Charles, the closest Underground Storage Tanks record about 2.5 miles out from the town centreFederal environmental registers
- St. Charles's boundary and the 469 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~149-day seasonGrowable Ground crop-matching engine
- The ecoregion at St. Charles's own centroid, the Wyoming BasinUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so St. Charles's 469 acres read through its county's SSURGO summaryfrom Bear Lake County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Bear Lake County
- The growing challenges every Idaho grower plans around — written at state scale, so they stay on the state guidefrom Idaho
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Bear Lake County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among St. Charles's 469 acreswhy one lot differs from the next →
- Which side of St. Charles you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 469 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 2.5 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 St. Charles-wide figureread your own land →