The Central Idaho Mountains spans USDA hardiness zones 5a-6a — a zone band wide enough that plant choice, not possibility, is the interesting question.
Idaho's shortest growing season: the central Rockies high country runs just 94 frost-free days at Valley County (McCall), 104 at Custer (Stanley/Challis), and 110–117 across Idaho and Lemhi (Salmon) — a full 30–50 days shorter than the Wood River Valley one range south (Blaine, 143 days), with cold-air pooling that can drop frost into any summer month. At 4,000–6,500 ft in USDA 5a–6a, growers here lean on season extension, short-season and short-day varieties, and careful frost-pocket siting rather than fighting the calendar. Among the crops suited to this profile: potato, lentil, apple, and hop. The site-level story — soil, sun, drainage — decides the rest.
The Central Idaho Mountains spans Idaho.
Your yard isn't all of the Central Idaho Mountains.
The Central Idaho Mountains spans USDA zones 5a-6a, but your parcel sits in exactly one — and slope, tree cover, and low spots nudge it further. 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 Central Idaho Mountains — soil, climate, flood, and parcel records. How we handle your address.
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The Central Idaho Mountains — the short answer
The Central Idaho Mountains: USDA zones 5a-6a, 94–117 frost-free days, in Idaho.
- USDA zones
- 5a-6a
- USDA PHZM 2023, aggregated over the footprint
- Frost-free season
- 94–117 days
- NOAA Regional Climate Centers ACIS, 1991-2020
- Counties
- 4
- US Census TIGER/Line 2025
- Region type
- County cluster
- Growable Ground growing-region registry
Region boundary: Growable Ground growing-region registry — curated county clusters, EPA Level III ecoregions, and town clusters drawn finer than any county. Where a region publishes no measured season, no season figure is shown.
Hardiness Zone Range
What Grows in the Central Idaho Mountains
Plants matched to the Central Idaho Mountains' USDA zones 5a-6a, ordered by how much hardiness margin each has across the region — the ones with room to spare at both ends of this band lead. Each links to its full growing profile.
Native Plants of the Central Idaho Mountains
Plants the USDA PLANTS Database documents as native and present in this region’s state, kept only where the published hardiness range meets the Central Idaho Mountains’s USDA zones 5a-6a — closest range match first. Presence is recorded by state, so a plant can be documented across the state and still be scarce in your corner of the region.
The ground across the Central Idaho Mountains
The USDA soil survey maps this ground county by county. These are those records weighted by land area across four member counties — this region’s own profile, not a state figure.
The ground is predominantly Mollisols, at 37% of mapped acres, followed by Inceptisols (30%), Aridisols (18%) and Andisols (8%). Eight soil orders appear somewhere inside the footprint, which is the honest reason a regional soil answer only goes so far. The most extensive named soils are Pyle, Dawtonia, and Koppes.
71% of those acres are well drained, and another 13% somewhat excessively drained, 6% moderately well drained. Topsoil pH runs 5.8–7.9 between the lowest and the highest county on record. 1% of the footprint is classed prime farmland.
Soil order
Mollisols
Drainage
Well drained
Topsoil pH
5.8–7.9
Hydric soils
3%
Soil changes across a driveway, so which of these your own ground sits on is a parcel question rather than a regional one. Valley County holds the most wetland ground here, at 6% — soil types explained.
USDA NRCS SSURGO via Soil Data Access
What this means for growing in the Central Idaho Mountains
The soil survey reads this ground county by county, and the readings above are those records summed across the Central Idaho Mountains. Here is what they mean for a garden here — and the move an experienced grower makes about each one.
Drainage
From county records71% of the mapped acres across the Central Idaho Mountains are well drained — ground that drains quickly. That is area-weighted across all four of its mapped counties.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
From county recordsTopsoil across the Central Idaho Mountains runs pH 5.8–7.9 — near neutral in two of its four counties.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Safe to Grow Here?
What the federal record shows across the Central Idaho Mountains — and how to grow with it.
Across the Central Idaho Mountains' 4 counties the federal record holds 2,098 documented sites, mostly Mining (1,382), Nitrate (330) and Underground Storage Tanks (299). The heaviest single county is Lemhi County, with 619.
That is a regional count, not a reading of any one lot — proximity to a documented site is information, not a diagnosis. Open the map outlined to the Central Idaho Mountains to see which records sit where you actually grow.
Sources Checked
Summed across the 4 counties in the Central Idaho Mountains
A note from Gnorman
What an experienced grower watches for around here
In and around the Central Idaho Mountains, two things run higher than the national average across the 4 counties in the Central Idaho Mountains — Mining (1,382 sites) and Superfund (35 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.
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).
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Your land is one point inside the Central Idaho Mountains
Everything above resolves to the Central Idaho Mountains as a whole — a footprint spanning USDA zones 5a-6a. Your parcel sits in exactly one of them. 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 region 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 regional average.
Your Lot vs the Central Idaho Mountains Average
Central Idaho Mountains Average
- ●USDA Zones 5a-6a, averaged across Central Idaho Mountains
- ●One soil character for all of Central Idaho Mountains
- ●State-average frost dates
YOUR Parcel
- ✓Your exact zone, not Central Idaho Mountains' 5a-6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in the Central Idaho Mountains
Pull a site-specific report for your exact address in the Central Idaho Mountains — soil, sun, drainage, frost risk, contamination, and scored plant recommendations.
Three things about your lot that Central Idaho Mountains averages can't show:
We read public map data around The Central Idaho Mountains — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Central Idaho Mountains average
How we know this about the Central Idaho Mountains
The boundary: a cluster of neighboring counties. Growing regions have no official boundary, so this footprint is our published one, and every figure on this page was measured over the counties inside it rather than borrowed from the state around it.
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, aggregated across the footprint; the growing season from NOAA Regional Climate Centers ACIS 1991–2020 28°F normals, read at each member’s own record; boundaries from US Census TIGER/Line 2025; the contamination record from the federal sources named in that beat above; the soil from the USDA NRCS SSURGO survey, read at each member county’s own record and weighted to this footprint by land area. Where a member carries no record of its own, it is absent from the figure rather than filled in.
Common questions about the Central Idaho Mountains
What hardiness zone is the Central Idaho Mountains?
The Central Idaho Mountains spans USDA hardiness zones 5a-6a, aggregated from the USDA Agricultural Research Service Plant Hardiness Zone Map 2023 across the region's counties. Zones reflect average annual extreme minimum temperatures from 1991–2020 data.
How long is the growing season in the Central Idaho Mountains?
Measured between 28°F hard freezes, the Central Idaho Mountains' counties mostly run 102 to 112 frost-free days, median 107 (NOAA Regional Climate Centers ACIS, 1991–2020, over 4 member counties). That 10-day spread is the honest read — no single season describes 4 counties, and each county guide below carries its own.
When does frost risk end in the Central Idaho Mountains?
Across the Central Idaho Mountains, the middle half of member counties see their last 28°F hard freeze between May 27 and Jun 6 (median Jun 1), and their first fall freeze between Sep 14 and Sep 18. Those are hard freezes, not the last light frost: tender transplants wait for about Jun 22, and elevation decides which end of a 10-day spread you garden in.
What grows well in the Central Idaho Mountains?
The Central Idaho Mountains' conditions suit plants such as Potato, Lentil, Apple, Hop, Cherry. What actually thrives on any one site still turns on its specific soil, sun, and drainage — we score each plant against the real conditions at your address.
How is the Central Idaho Mountains defined?
The Central Idaho Mountains is defined here as a curated cluster of 4 neighboring counties that share a growing character. Growing regions have no official boundary, so this footprint is our published one — every county in it is named on this page.
Which states does the Central Idaho Mountains cover?
The Central Idaho Mountains spans Idaho. Each state's full growing guide is linked on this page.
What other growing regions cover the same states?
Columbia Basin, Snake River Plain, Eastern Idaho (Upper Snake River Valley), Magic Valley, Idaho Panhandle (North Idaho), and Treasure Valley share at least one state with the Central Idaho Mountains. Growing regions overlap and interlock — a single address can sit inside more than one, which is why the precise read is always the parcel, not the region.
What this page reads at the Central Idaho Mountains’s own scale
6 of the readings below were taken at the Central Idaho Mountains' own scale — the zone 5a-6a band across its footprint, a median 107-day season across its 4 counties and 2,098 documented federal contamination records across its 4 counties, 619 of them in Lemhi County alone; one is borrowed from a wider read, named and linked below.
Measured here
- The USDA hardiness band 5a-6a aggregated across all 4 counties in the footprintUSDA PHZM 2023
- The boundary itself — the 4 counties this region is curated fromGrowable Ground subregion registry
- The growing character that makes this region distinct from the states it crossesGrowable Ground subregion registry
- The 28°F season across the footprint — the middle half of its 4 counties run 102 to 112 frost-free days, median 107NOAA Regional Climate Centers ACIS, 1991-2020
- The federal contamination record over the whole footprint — 2,098 documented federal contamination records across its 4 counties, 619 of them in Lemhi County aloneEPA, USGS and USDA federal site records
- The soil order mix across the footprint — 37% Mollisols, topsoil pH 5.8–7.9, area-weighted across its 4 mapped countiesUSDA NRCS SSURGO
Inherited from a wider read
- The candidate plant list — its state's curated sets, merged and filtered to zones 5a-6afrom Idaho
What this page can’t tell you
- Which end of the 10-day range your ground sits at — 102 days at one extreme, 112 at the other, decided mostly by elevationfrost dates explained →
- Which of those soils your own ground sits on — the survey maps them county-wide, and they change across a drivewaysoil types explained →
- The soil pH, drainage, sun hours, and frost pockets on one specific lotwhy one lot differs from the next →
Explore the Central Idaho Mountains
State growing guides
Counties in this region
Other growing regions across Idaho
A dry basalt plateau of loess soils in the inland Northwest where irrigation turns arid ground into apple, cherry, hop, and wine-grape country.
A broad volcanic plain of deep ash-rich soils and long summer days, irrigated from the Snake River — the classic Idaho potato, hop, and sugar-beet country.
Eastern Idaho's Upper Snake River Valley is the cold, high-elevation head of the same volcanic plain that gives Boise its 7a warmth — but here the growing reality inverts. At roughly 4,500–6,000 ft, Idaho Falls, Pocatello, and Rexburg sit in USDA zones 5a–5b with about 130–165 frost-free days at the population centers (shorter still in the outlying mountain valleys like Bear Lake and Caribou), running 1.5–2 zones colder and 40–70 days shorter than the Treasure Valley downstream. Routine late-May frosts make this short-season, cold-hardy, high-desert growing — the mirror image of the plain's warm western end that the broad Snake River Plain page averages away.
The irrigated heart of south-central Idaho, where Snake River canal water — the "magic" that turned high desert into cropland after the 1905 Milner Dam and the Carey Act land tracts — feeds a tight 6a–6b band on volcanic-ash soils at roughly 3,700 feet. Cooler and far more uniform than the wider Snake River Plain that runs from balmy Boise (7a) to the frosty eastern plain (5b), this is Idaho's dairy, sugar-beet, dry-edible-bean, and malting-barley heartland, with the Snake River Canyon and Shoshone Falls cutting straight through it.
Forested, lake-and-mountain far-north Idaho — nothing like the arid Snake River Plain or the treeless Palouse wheat prairie to the south. Big glacial lakes (Pend Oreille, Coeur d'Alene) buffer both spring frost and summer heat across a humid-continental, higher-precipitation belt of cedar-and-hemlock forest soils. Expect USDA zones 6a–6b and a cool, wet-spring season of roughly 148–187 frost-free days (verified county climate data), with last frosts into mid-May in the northern valleys — a short, moist window the southern-Idaho and Palouse pages can't describe.
Idaho's Boise-anchored growing corridor: the warm valley floor around Ada and Canyon counties reaches roughly 200 frost-free days at USDA zone 7a, while the Boise and Owyhee foothills that ring it run up to a full zone colder on a markedly shorter season.