Lemhi County, in Idaho, sits in USDA hardiness zone 6a — a zone band wide enough that plant choice, not possibility, is the interesting question.
On paper, okra, blackberry, california poppy, and pumpkin all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Lemhi County lies within the Central Idaho Mountains — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Lemhi County holds more than one microclimate.
Soils and elevations shift across Lemhi County, so your frost dates and drainage aren't the county average. 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 Lemhi County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Lemhi County — the short answer
Lemhi County, Idaho: USDA zone 6a, about 117 days between hard freezes, across 2.9M acres.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 29
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Sep 23
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~117
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 2.9M acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 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 Lemhi County's average, not your lot's — a low corner or a tree line moves it. Against Lemhi County's 117-day season, see what your own ground reads.
Heat in Lemhi County
Across a year, Lemhi County accumulates about 913 growing degree days above 50°F, about 578 fewer than the middle Idaho county — ahead of 2 of Idaho’s 44 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Lemhi County
Across Lemhi County, the ground is predominantly Mollisols, where Millhi, Pahsimeroi, and Dawtonia are the most extensive named soil series. The soil is generally well drained with a gravelly loam surface. Topsoil pH runs about 7.0–7.9, slightly alkaline. Rainfall drains through hydrologic group B soils.
Soil order
Mollisols
Drainage
Well drained
Hydric soils
4%
Soil still varies lot by lot — soil types explained.
How the ground varies across Lemhi County
The USDA soil survey maps 74% of Lemhi County as well drained — but another 24% drains differently: 11% somewhat excessively drained, 7% moderately well drained.
Millhi is the most extensive named soil at 4% of mapped acres, then Pahsimeroi (4%) and Dawtonia (4%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Lemhi County
Each reading below is measured for Lemhi County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Lemhi County are well drained, in hydrologic group B — ground that drains quickly.
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
MeasuredTopsoil across Lemhi County runs about pH 7.0–7.9, on the alkaline side.
Many vegetables cope, but acid-lovers like blueberries struggle, and iron and manganese lock up above about pH 7.5 — leaves yellow between the veins even in rich soil.
Elemental sulfur and generous organic matter lower pH slowly for the beds that need it; test first so you add only what the soil actually calls for.
USDA NRCS SSURGO
Season length
MeasuredLemhi County runs about 117 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
MeasuredLemhi County 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 Lemhi County is in
Lemhi County spans 2 EPA Level III ecoregions — Middle Rockies (52%) and Idaho Batholith (48%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Lemhi County
We scored all 1,086 plants against Lemhi County's own USDA zone 6a and its own 117-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Idaho profile.
Is it too late to plant in Lemhi County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around May 1; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 29 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 23 — long-season crops need about 90 days of runway, quick greens only 30. When the window is tight, the fall moves are quick ones — baby greens, radishes, and garlic set for next season.
Documented around Lemhi County
- monarch butterfly3 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Lemhi County
USGS estimates 4,180 lb of 2,4-d on Lemhi County farmland in 2019, its largest by weight, ahead of Glyphosate (3,254 lb) and Diuron (851 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Lemhi County — and how to grow with it.
We checked the federal record across Lemhi County — 619 documented sites across 7 of the 9 source types we track.
The most significant on record: 3 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Lemhi County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Lemhi County
Closest first, across Lemhi County. Listing isn't leaking, and distance isn't exposure.
- Birthday ClaimMining · 3.8 mi
- 19N 21E 14DBD1Nitrate · 4.1 mi
- ELK BEND SPORT LODGEUnderground Storage Tanks · 4.4 mi
- Nautalis ClaimsMining · 4.7 mi
- HUGHES CR FIELD STATIONUnderground Storage Tanks · 4.8 mi
- OLD BEAM PLANT SALESUnderground Storage Tanks · 4.8 mi
- Fire Fly ClaimMining · 4.9 mi
- Fire FlyMining · 4.9 mi
- Copper King ProspectMining · 5.3 mi
- Copper ProspectMining · 5.8 mi
- McDevitt Creek ProspectMining · 5.8 mi
- Twin Peaks MineMining · 6.1 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Lemhi County'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 Lemhi County.
Severity Distribution
across Lemhi County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Lemhi County, Mining runs higher than the national average — 469 sites across Lemhi County. 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.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Lemhi County
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 Lemhi County average
Your land is one point inside Lemhi County
Everything above resolves to Lemhi County as a whole — one PHZM band and one county frost record, read across 2.9M 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 county 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 county average.
Your Lot vs the Lemhi County Average
Lemhi County Average
- ●USDA Zones 6a, averaged across Lemhi County
- ●One soil character for all of Lemhi County
- ●Frost dates read at Lemhi County's scale: May 29 to Sep 23
YOUR Parcel
- ✓Your exact zone, not Lemhi County's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Lemhi County
Pull a site-specific report for your exact address in Lemhi County, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Lemhi County averages can't show:
We read public map data around Lemhi County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Lemhi County average
How we know this about Lemhi County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Lemhi County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Lemhi County
When does frost risk typically end in Lemhi County?
The last hard freeze (28°F) in Lemhi County typically lands around May 29, 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 19.
How long is the growing season in Lemhi County?
Measured between 28°F hard freezes, Lemhi County sees about 117 frost-free days — roughly May 29 through Sep 23, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 19 to Sep 9, about 82 days.
Is the soil safe to grow vegetables in Lemhi County?
The federal record around Lemhi County runs heavier than most — 619 documented sites, mostly Mining entries (469), the nearest Mining record about 3.8 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 Lemhi County?
With about 117 frost-free days between hard freezes, Lemhi County 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 145 to 173 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 29 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Lemhi County's scale — its 6a band and its 117-day season. Your yard writes its own version of Lemhi County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Idaho's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Lemhi County’s own scale
9 of the readings below were taken at Lemhi County's own scale — its own ~117-day span between 28°F freezes, the 3 most extensive soil series mapped here and 619 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Lemhi County's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Lemhi County's own 28°F hard-freeze dates and its ~117-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Lemhi CountyUSDA NRCS SSURGO
- 619 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 3.8 miles outFederal environmental registers
- Lemhi County's boundary and the 2,920,768 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~117-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Lemhi County spans, Middle Rockies the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Lemhi County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Lemhi County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Idaho grower plans around — written at state scale, so they stay on the state guidefrom Idaho
What this page can’t tell you
- How the season shifts across Lemhi County — the ~117 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Lemhi County's 2,920,768 acreswhy one lot differs from the next →
- Which of those 619 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Lemhi Countyread your own land →