Idaho City, Idaho, sits in USDA hardiness zone 6a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
A short list that earns its place here — cabbage, blackberry, california poppy, and collard greens — with any one site's soil, sun, and drainage making the final cut.
Even in Idaho 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 Idaho 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 Idaho City — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Idaho City — the short answer
Idaho City, Idaho: USDA zone 6a, about 136 days between hard freezes, across 426 acres of city.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 15
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Sep 28
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~136
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 426 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 Idaho City's average, not your lot's — a low corner or a tree line moves it. Against Idaho City's 136-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Idaho City
Each reading below is measured for Idaho City itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredIdaho City runs about 136 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
MeasuredIdaho 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 Idaho City is in
Idaho City sits in the Idaho Batholith — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Idaho City's own centroid rather than borrowed from Boise County.
What Grows in Idaho City
Every plant below cleared Idaho City's own zone 6a and its 136-day season. Each card opens that plant's Idaho profile. How we score.
Is it too late to plant in Idaho City?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Apr 17; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 15 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 28 — long-season crops need about 90 days of runway, quick greens only 30. In a season this compact, fast finishers and cold-hardy greens do the late work, and garlic tucked in before the freeze repays you next summer.
What's on the federal record near Idaho City
Closest first, within ~10 miles of Idaho City. Listing isn't leaking, and distance isn't exposure.
- BOISE BASIN MERCANTILEUnderground Storage Tanks · 750 ft
- GOLD HILL AND IOWA MINESSuperfund · 800 ft
- BASIN SCHOOLUnderground Storage Tanks · 1100 ft
- 06N 05E 26CBB1Nitrate · 2200 ft
- 06N 05E 34ABA1Nitrate · 0.9 mi
- Mud Springs ProspectMining · 2.3 mi
- 05N 05E 04ABB2Nitrate · 2.3 mi
- 05N 05E 04ABB1Nitrate · 2.3 mi
- Antimony LodeMining · 2.7 mi
- Antimony ProspectMining · 2.7 mi
- Garrecht ProspectsMining · 2.9 mi
- Morning Mist Mining CorporationMining · 3.1 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Idaho 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 Idaho City.
Total Sites
60
within ~10 miles of Idaho City
Risk Level
High
Highest-severity
3 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Idaho City
Severity Distribution
within ~10 miles of Idaho City
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Idaho City, two things run higher than the national average within ~10 miles of Idaho City — Mining (30 sites) and Superfund (3 sites). That's not a problem with your land — it's information about it.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Check your specific parcel in Idaho 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 Idaho City average
Your land is one point inside Idaho City
Everything above resolves to Idaho City as a whole — one PHZM band and one 28°F frost record, read across 426 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 Idaho City Average
Idaho City Average
- ●USDA Zones 6a, averaged across Idaho City
- ●One soil character for all of Idaho City
- ●Frost dates read at Idaho City's scale: May 15 to Sep 28
YOUR Parcel
- ✓Your exact zone, not Idaho City's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Idaho City
Pull a site-specific report for your exact address in Idaho City, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Idaho City averages can't show:
We read public map data around Idaho City — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Idaho City average
How we know this about Idaho 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 Idaho 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 Idaho City
When does frost risk typically end in Idaho City?
The last hard freeze (28°F) in Idaho City typically lands around May 15, 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 Jun 5.
When is the first frost in Idaho City?
The first hard freeze (28°F) in Idaho City typically arrives around Sep 28, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 14, so the watching starts about Aug 29 — about 136 days after the spring freeze cleared.
How long is the growing season in Idaho City?
Measured between 28°F hard freezes, Idaho City sees about 136 frost-free days — roughly May 15 through Sep 28, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 5 to Sep 14, about 101 days.
Is the soil safe to grow vegetables in Idaho City?
The federal record around Idaho City runs heavier than most — 60 documented sites, mostly Mining entries (30), the nearest Underground Storage Tanks record about 0.1 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 gardeners stretch the season in Idaho City?
With about 136 frost-free days between hard freezes, Idaho City 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 164 to 192 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 15 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Idaho City's scale — its 6a band and its 136-day season. Your yard writes its own version of Idaho 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 Idaho City’s own scale
6 of the readings below were taken at Idaho City's own scale — its own ~136-day season between 28°F freezes, the 426 acres it covers and 60 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Idaho City's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Idaho City's own 28°F hard-freeze dates, about May 15 and Sep 28 and the ~136-day span between themNOAA 1991–2020 Climate Normals
- 60 documented contamination sites on the federal record near Idaho City, the closest Underground Storage Tanks record about 0.1 miles out from the town centreFederal environmental registers
- Idaho City's boundary and the 426 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~136-day seasonGrowable Ground crop-matching engine
- The ecoregion at Idaho City's own centroid, the Idaho BatholithUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Idaho City's 426 acres read through its county's SSURGO summaryfrom Boise County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Boise 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 Boise County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Idaho City's 426 acreswhy one lot differs from the next →
- Which side of Idaho 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 426 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.1 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 Idaho City-wide figureread your own land →
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