Idaho spans USDA hardiness zones 3b-8a, with a growing season of about 160 frost-free days — a season that fits spring and fall plantings of cool-weather crops around a solid warm-season core.
In practice the season is written by 8-35 inches of annual rainfall, a median of roughly 1,187 growing-degree days (base 50°F), and about 2,500 winter chill hours for tree fruit. The ground itself runs to volcanic ash, silt loam, sandy loam, and basalt-derived; drainage character, more than fertility, is usually what sorts the thrivers from the strugglers. Idaho splits into distinct growing country: Columbia Basin, Snake River Plain, and Eastern Idaho (Upper Snake River Valley), each keeping its own frost calendar. A short list that earns its place here — potato, apple, hop, and cherry — with any one site's soil, sun, and drainage making the final cut.
Grounded inUSDA PHZM•NOAA Climate Normals•USDA NRCS SSURGO•GDD (PRISM 1991-2020 normals)•Chill hours (PRISM 1991-2020 normals)•USDA hardiness sub-region map•EPA FRS•USDA PLANTS•Growable Ground suitability scoring
Idaho spans zones 3b-8a, but your yard 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 Idaho — soil, climate, flood, and parcel records. How we handle your address.
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Distinct growing regions within Idaho — each has its own zones, soils, and signature crops.
Idaho: USDA zones 3b-8a, 94–216 frost-free days depending on the county, 44 counties.
The middle half of this state’s counties. Tender transplants usually wait 2–3 weeks past the last hard freeze. The shortest-season figure is Idaho's own county record — Valley County's measured 28°F normal, not a modeled floor.
Zone 3b-8a is Idaho's average, not your lot's — a low corner or a tree line moves it. Against Idaho's 160-day season, see what your own ground reads.
One answer for Idaho averages 44 counties whose growing seasons are 122 days apart — from 94 frost-free days in Valley County to 216 in Nez Perce County. That is the same state, measured the same way, in the same years. Which end of it your county sits nearer decides what finishes before the first hard freeze.
The middle half of 44 counties runs 133–174 days, with a median of 159 days — a 122-day span end to end.
Measured across 44 counties, each carrying its own 28°F normal. NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze. A county with no record of its own is absent from the range rather than counted as zero — nothing here is interpolated to the state. Your own site sits somewhere inside this range; a parcel report resolves where.
The middle half of Idaho runs 133–174 frost-free days, and 21 of its 44 counties sit outside that — 10 on the short side, 11 on the long. A statewide planting date describes the middle well and the ends poorly, which is worth knowing before you follow one.
Under 133 frost-free days
10 counties
3 of 10 shown
The end of the state that sets the planting calendar — start seed indoors here and the season stretches to meet the crop.
133–174 frost-free days
23 counties
0 of 23 shown
The middle half of the state, and the part a single statewide date describes well.
Over 174 frost-free days
11 counties
3 of 11 shown
Long enough for a second succession of a quick crop after the first comes out.
Each county is placed by its own 28°F frost-free normal (NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze), the same figure its own guide page publishes. Elevation, slope and cold-air drainage move a yard within its county as well — which is the part only your address resolves.
The soil types that dominate Idaho — how each drains decides more about crop success than almost anything else. Tap any soil to learn what it is and how to work with it. Each photo is a representative profile of that soil type; the named series is where it was documented, which is often another state.
Drainage
Excellent and unusual: ash soils drain freely yet hold remarkable amounts of plant-available water in their porous structure — the best of both habits.
What thrives
Volcanic regions grow celebrated crops the world over: orchards, berries, vegetables, coffee, and wine grapes all prosper on ash-derived soils.
Drainage
Moderate. Silt holds water well and releases it steadily, though the fine particles can crust after hard rain and compact under traffic.
What thrives
The full vegetable garden does well here, and small grains, corn, and leafy greens are classic silt-loam crops. Its steady moisture suits shallow-rooted plants that dislike drought stress.
Drainage
Fast. The sand fraction opens the soil up, so water moves through the root zone quickly and the surface rarely stays soggy. The trade is that nutrients ride out with the water.
What thrives
Root crops love it — carrots, potatoes, radishes, and onions size up cleanly in ground they can push through. Melons, sweet potatoes, asparagus, and most herbs appreciate the warmth and the drainage.
Drainage
Generally good; basalt soils range from stony and fast-draining on young flows to deeper clay loams on old ones.
What thrives
Wine grapes, orchard fruit, and vegetables all do famously well on basalt-derived soils — volcanic mineral wealth shows up in the harvest.
Soil data: USDA NRCS SSURGO · Soil types explained
Plants well-suited to Idaho's climate, soils, and growing season — each links to its full growing profile.
Rarely: the season closes in stages, not all at once, and each stage has its crops. Across Idaho, cool-season planting typically opens about four weeks before the local last hard freeze — county medians put that freeze near May 4, with the middle half of counties between Apr 26 and May 17 (NOAA 1991–2020 climate normals). Tender transplants wait two to three weeks past it, and fall planting counts back from first freezes mostly between Oct 1 and Oct 17 — long-season crops need about 90 days of runway, quick greens only 30. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
The plants Idaho put its name on — cultural emblems, not growing recommendations.
Syringa (mock orange)
Philadelphus lewisii
Designated 1931.
Western white pine
Pinus monticola
Designated 1935.
Designated 2000. In our plant library — see its full growing profile.
Plants the USDA PLANTS Database documents as native and present in Idaho — a real per-state range, not just a zone match. Ordered by how closely each plant’s published hardiness range matches Idaho’s zones 3b-8a, so this is a shortlist by climate fit, not a ranking of which plants matter most here. Presence is statewide, so a plant may still be uncommon in your specific county; your state’s Cooperative Extension or a native-plant society is the local authority.
US-native plants whose hardiness range overlaps Idaho’s USDA zones 3b-8a but which USDA PLANTS doesn’t map to a single state range here. Zone overlap is a starting filter, not a range map.
What an experienced grower plans around here — each one has a move.
Short growing season at higher elevations
At elevation, fast varieties plus a cold frame or low tunnel reliably buy back the weeks the calendar withholds.
Arid conditions require irrigation in most of the state
Drip irrigation and deep mulch are the arid-country baseline — set the water system before the plants.
Cold winter snaps can reach -30F in mountain valleys
Plant perennials for your real zone, not an optimistic one — a -30°F night finds every zone-pushed plant.
For cultivar selection, pest pressure, and planting-time guidance specific to Idaho, the University of Idaho Extension is the authoritative local source.
Safe to Grow Here?What the federal record shows across Idaho — and how to grow with it.
We checked the federal record across Idaho — 21,100 documented sites across 8 of the 9 source types we track.
The most significant on record: 215 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Idaho 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.
Severity Distribution
across Idaho
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Idaho, two things run higher than the national average across Idaho — Mining (3,980 sites) and Nitrate (9,840 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).
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Everything above resolves to Idaho as a whole — a state whose own counties record seasons 122 days apart, and hardiness across zones 3b-8a. Your parcel sits at one point in that range, not in the middle of it. 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 state 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 statewide average.
State averages sketch the shape. Your soil, sun exposure, drainage, and microclimate decide what actually takes. Pull a site-specific report for your exact parcel.
Enter your address. We read your soil, sun, drainage, and frost dates, then score 1,086 plants against the real conditions on your land.
Three things about your lot that Idaho averages can't show:
We read public map data around Idaho — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Idaho average
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read per county and aggregated to the state band; the growing season from NOAA Regional Climate Centers ACIS 1991–2020 28°F normals, read at each county’s own record; rainfall from NOAA Climate Normals; soils from USDA NRCS SSURGO; boundaries from US Census TIGER/Line 2025; the contamination record from the federal sources named in that beat above. Where a county carries no record of its own, it is absent from the figure rather than filled in.
Idaho spans USDA hardiness zones 3b-8a — which is to say winter's coldest night runs from about −35°F to 15°F depending where in Idaho you are, averaged over 1991–2020 (USDA PHZM 2023).
Rarely: the season closes in stages, not all at once, and each stage has its crops. Across Idaho, cool-season planting typically opens about four weeks before the local last hard freeze — county medians put that freeze near May 4, with the middle half of counties between Apr 26 and May 17 (NOAA 1991–2020 climate normals). Tender transplants wait two to three weeks past it, and fall planting counts back from first freezes mostly between Oct 1 and Oct 17 — long-season crops need about 90 days of runway, quick greens only 30. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
Across Idaho, the middle half of counties see their last hard freeze (28°F) between about Apr 26 and May 17, with a county median near May 4 (NOAA 1991–2020 climate normals). 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 25.
Measured between 28°F hard freezes, growing seasons across Idaho's counties mostly run about 133 to 175 days, with a county median near 160 (NOAA 1991–2020 climate normals). Tender crops get a somewhat shorter practical window, since lighter frosts reach a few weeks past the hard-freeze dates on both ends.
Idaho's zones 3b-8a support a wide range — strong performers include Potato, Apple, Hop, Cherry, and Lentil. What actually takes on any one site comes down to its soil, sun, and drainage, and we score each plant against the real conditions at your address.
Officially, Idaho spans USDA zones 3b-8a (USDA PHZM 2023) — but a zone is a 30-year average of winter's coldest night across an area, and it can't see any one yard. A south-facing slope, a tree line, or a low frost pocket can shift a single site by half a zone either way, which is why neighboring gardeners often quote different numbers. We read the conditions at your exact address — soil, sun, slope, and frost — and score 1,086 plants against what's actually there.
The federal record across Idaho runs heavier than most — 21,100 documented sites, mostly Nitrate entries (9,840) — 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.
Start with three facts. Idaho spans USDA zones 3b-8a, which sets what survives winter; last hard freezes range from about Apr 26 to May 17 across its counties (NOAA 1991–2020 climate normals); and 21,100 documented sites sit on the federal record here, so a soil test before food beds is the smart first step. From there, matching plants to your actual soil and sun is the fun part.
Everything above is measured at Idaho's scale — its 3b-8a band and its 160-day season. Your yard writes its own version of Idaho's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
6 of the readings below were taken at Idaho's own scale — the full zone 3b-8a span inside its borders, the 4 soil types that dominate its ground and 21,100 documented sites on its federal record; anything it cannot resolve at this scale is named below.
Measured here
What this page can’t tell you
Explore growing conditions by county — each has its own zone range and land area.
Explore growing conditions by city or town in Idaho.
