Twin Falls 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.
Twin Falls 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
Twin Falls County holds more than one microclimate.
Soils and elevations shift across Twin Falls 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 Twin Falls County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Twin Falls County — the short answer
Twin Falls County, Idaho: USDA zone 6b, about 172 days between hard freezes, across 1.2M acres.
- USDA zone
- 6b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 27
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 16
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~172
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 1.2M 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 Twin Falls County's average, not your lot's — a low corner or a tree line moves it. Against Twin Falls County's 172-day season, see what your own ground reads.
Heat in Twin Falls County
Across a year, Twin Falls County accumulates about 1,990 growing degree days above 50°F, about 499 more than the middle Idaho county — ahead of 33 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 Twin Falls County
Across Twin Falls County, the ground is predominantly Aridisols, where Portneuf, Chuska, and Sluka are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 7.0–7.9, slightly alkaline. Rainfall drains through hydrologic group D soils.
Soil order
Aridisols
Drainage
Well drained
Hydric soils
0%
Soil still varies lot by lot — soil types explained.
How the ground varies across Twin Falls County
The USDA soil survey maps 95% of Twin Falls County as well drained — but another 1% drains differently: 1% moderately well drained.
Portneuf is the most extensive named soil at 11% of mapped acres, then Chuska (9%) and Sluka (7%).
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 Twin Falls County
Each reading below is measured for Twin Falls 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 Twin Falls County are well drained, in hydrologic group D — 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 Twin Falls 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
MeasuredTwin Falls County runs about 172 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredTwin Falls 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 Twin Falls County is in
Twin Falls County spans 2 EPA Level III ecoregions — Northern Basin and Range (66%) and Snake River Plain (34%). 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 Twin Falls County
We scored all 1,086 plants against Twin Falls County's own USDA zone 6b and its own 172-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 Twin Falls County?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Mar 30; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 27 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 16 — long-season crops need about 90 days of runway, quick greens only 30. Even past midsummer there is room for a true fall garden here, and garlic planted near the close carries the momentum into next year.
Documented around Twin Falls County
- monarch butterfly2 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Twin Falls County
USGS estimates 97,322 lb of Glyphosate on Twin Falls County farmland in 2019, its largest by weight, ahead of Acetochlor (12,982 lb) and Chlorpyrifos (11,918 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 Twin Falls County — and how to grow with it.
We checked the federal record across Twin Falls County — 1,036 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.
There's a meaningful federal record across Twin Falls County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Twin Falls County
Closest first, across Twin Falls County. Listing isn't leaking, and distance isn't exposure.
- 12S 15E 35AAA1Nitrate · 0.8 mi
- 12S 15E 26AAA1Nitrate · 0.8 mi
- 12S 15E 35DDD1Nitrate · 1.5 mi
- 13S 15E 01CCC1Nitrate · 2.5 mi
- 13S 16E 12BCC1Nitrate · 3.0 mi
- 13S 16E 07BBC1Nitrate · 3.0 mi
- 12S 15E 10CBB1Nitrate · 3.3 mi
- 13S 16E 07AAA1Nitrate · 3.5 mi
- 13S 16E 08BBAC1Nitrate · 3.8 mi
- Oasis Stop N Go #23Underground Storage Tanks · 4.6 mi
- SMOKY'S BAR AND GRILLUnderground Storage Tanks · 4.6 mi
- 12S 16E 34BCA1Nitrate · 4.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Twin Falls 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 Twin Falls County.
Total Sites
1,036
across Twin Falls County
Risk Level
Elevated
Highest-severity
6 Superfund sites (none NPL-listed)
Sources Checked
across Twin Falls County
Severity Distribution
across Twin Falls County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Twin Falls County, two things run higher than the national average across Twin Falls County — CAFO (22 sites) and Nitrate (574 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
CAFO: CAFOs pose a different contamination profile than chemical sources.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Twin Falls 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 Twin Falls County average
Your land is one point inside Twin Falls County
Everything above resolves to Twin Falls County as a whole — one PHZM band and one county frost record, read across 1.2M 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 Twin Falls County Average
Twin Falls County Average
- ●USDA Zones 6b, averaged across Twin Falls County
- ●One soil character for all of Twin Falls County
- ●Frost dates read at Twin Falls County's scale: Apr 27 to Oct 16
YOUR Parcel
- ✓Your exact zone, not Twin Falls County's 6b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Twin Falls County
Pull a site-specific report for your exact address in Twin Falls County, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Twin Falls County averages can't show:
We read public map data around Twin Falls County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Twin Falls County average
How we know this about Twin Falls 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 Twin Falls County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Twin Falls County
When does frost risk typically end in Twin Falls County?
The last hard freeze (28°F) in Twin Falls County typically lands around Apr 27, 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 May 18.
How long is the growing season in Twin Falls County?
Measured between 28°F hard freezes, Twin Falls County sees about 172 frost-free days — roughly Apr 27 through Oct 16, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 18 to Oct 2, about 137 days.
Is the soil safe to grow vegetables in Twin Falls County?
The federal record around Twin Falls County is a meaningful one — 1,036 documented sites, mostly Nitrate entries (574), the nearest Nitrate record about 0.8 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
Everything above is measured at Twin Falls County's scale — its 6b band and its 172-day season. Your yard writes its own version of Twin Falls 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 Twin Falls County’s own scale
9 of the readings below were taken at Twin Falls County's own scale — its own ~172-day span between 28°F freezes, the 3 most extensive soil series mapped here and 1,036 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Twin Falls County's own USDA hardiness band, zones 6bUSDA PHZM 2023
- Twin Falls County's own 28°F hard-freeze dates and its ~172-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Twin Falls CountyUSDA NRCS SSURGO
- 1,036 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 0.8 miles outFederal environmental registers
- Twin Falls County's boundary and the 1,229,897 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6b and a ~172-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Twin Falls County spans, Northern Basin and Range the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Twin Falls County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Twin Falls 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 Twin Falls County — the ~172 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 Twin Falls County's 1,229,897 acreswhy one lot differs from the next →
- Which of those 1,036 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 Twin Falls Countyread your own land →