Cassia County, in Idaho, sits in USDA hardiness zone 6b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Reliable performers under these conditions include cabbage, blackberry, california poppy, and collard greens; what your own ground favors still comes down to its soil, sun, and drainage.
Cassia County lies within the Magic Valley — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Cassia County holds more than one microclimate.
Soils and elevations shift across Cassia 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 Cassia County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Cassia County — the short answer
Cassia County, Idaho: USDA zone 6b, about 130 days between hard freezes, across 1.6M acres.
- USDA zone
- 6b
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 25
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 2
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~130
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 1.6M 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 6b is Cassia County's average, not your lot's — a low corner or a tree line moves it. Against Cassia County's 130-day season, see what your own ground reads.
Heat in Cassia County
Across a year, Cassia County accumulates about 1,171 growing degree days above 50°F, about 320 fewer than the middle Idaho county — ahead of 13 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 Cassia County
Across Cassia County, the ground is predominantly Aridisols, where Declo, Darkbull, and Portneuf are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 7.3–8.2, slightly alkaline. Rainfall drains through hydrologic group B soils.
Soil order
Aridisols
Drainage
Well drained
Hydric soils
1%
Soil still varies lot by lot — soil types explained.
How the ground varies across Cassia County
The USDA soil survey maps 91% of Cassia County as well drained — but another 8% drains differently: 3% somewhat excessively drained, 2% moderately well drained.
Declo is the most extensive named soil at 7% of mapped acres, then Darkbull (6%) and Portneuf (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 Cassia County
Each reading below is measured for Cassia 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 Cassia 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 Cassia County runs about pH 7.3–8.2, 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
MeasuredCassia County runs about 130 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
MeasuredCassia County sits in USDA hardiness zone 6b.
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 Cassia County is in
Cassia County spans 2 EPA Level III ecoregions — Northern Basin and Range (78%) and Snake River Plain (22%). 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 Cassia County
We scored all 1,086 plants against Cassia County's own USDA zone 6b and its own 130-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 Cassia County?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Apr 27; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 25 (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. Even here the calendar’s edges hold value: thirty-day greens late in the window, then garlic and a rested bed for spring.
Documented around Cassia County
- monarch butterfly8 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Cassia County
USGS estimates 110,753 lb of Glyphosate on Cassia County farmland in 2019, its largest by weight, ahead of Chlorpyrifos (25,686 lb) and 2,4-d (24,326 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 Cassia County — and how to grow with it.
We checked the federal record across Cassia County — 542 documented sites across 8 of the 9 source types we track.
The most significant on record: 6 Superfund sites (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Cassia 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 Cassia County
Closest first, across Cassia County. Listing isn't leaking, and distance isn't exposure.
- Golden Eagle MineMining · 1.8 mi
- Harris and Hume ProspectMining · 2.2 mi
- Albion Group MineMining · 2.7 mi
- Giant LodeMining · 2.9 mi
- ExcelsiorMining · 3.2 mi
- Big Bertha GroupMining · 3.2 mi
- Connor ProspectMining · 3.9 mi
- Melcher MineMining · 4.0 mi
- Boulder Creek ProspectMining · 4.1 mi
- Unnamed LocationMining · 4.1 mi
- 13S 25E 32AAB1Nitrate · 4.2 mi
- 13S 25E 22BCB1Nitrate · 4.9 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Cassia 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 Cassia County.
Severity Distribution
across Cassia County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Cassia County, two things run higher than the national average across Cassia County — Nitrate (288 sites) and Mining (44 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
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 well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Cassia 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 Cassia County average
Your land is one point inside Cassia County
Everything above resolves to Cassia County as a whole — one PHZM band and one county frost record, read across 1.6M 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 Cassia County Average
Cassia County Average
- ●USDA Zones 6b, averaged across Cassia County
- ●One soil character for all of Cassia County
- ●Frost dates read at Cassia County's scale: May 25 to Oct 2
YOUR Parcel
- ✓Your exact zone, not Cassia County's 6b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Cassia County
Pull a site-specific report for your exact address in Cassia County, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Cassia County averages can't show:
We read public map data around Cassia County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Cassia County average
How we know this about Cassia 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 Cassia County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Cassia County
When does frost risk typically end in Cassia County?
The last hard freeze (28°F) in Cassia County typically lands around May 25, 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 15.
How long is the growing season in Cassia County?
Measured between 28°F hard freezes, Cassia County sees about 130 frost-free days — roughly May 25 through Oct 2, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 15 to Sep 18, about 95 days.
Is the soil safe to grow vegetables in Cassia County?
The federal record around Cassia County runs heavier than most — 542 documented sites, mostly Nitrate entries (288), the nearest Mining record about 1.8 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 Cassia County?
With about 130 frost-free days between hard freezes, Cassia 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 158 to 186 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 25 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Cassia County's scale — its 6b band and its 130-day season. Your yard writes its own version of Cassia 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 Cassia County’s own scale
9 of the readings below were taken at Cassia County's own scale — its own ~130-day span between 28°F freezes, the 3 most extensive soil series mapped here and 542 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Cassia County's own USDA hardiness band, zones 6bUSDA PHZM 2023
- Cassia County's own 28°F hard-freeze dates and its ~130-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Cassia CountyUSDA NRCS SSURGO
- 542 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 1.8 miles outFederal environmental registers
- Cassia County's boundary and the 1,641,989 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6b and a ~130-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Cassia County spans, Northern Basin and Range the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Cassia County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Cassia 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 Cassia County — the ~130 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 Cassia County's 1,641,989 acreswhy one lot differs from the next →
- Which of those 542 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 Cassia Countyread your own land →