Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for Twin Falls, ID

Twin Falls, ID is in USDA zone 6b across its 2 ZIP codes. The median last spring frost is May 9 and the first fall frost October 4.

Twin Falls on the zone map

Outlined: its 1 ZIP code areas · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone6b−5 to 0 °F
ZIP codes2
Last frostMay 9
First frostOct 4
Growing season147 days

6b 2 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

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Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Twin Falls, ID

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 9median — 50% chance of a later frost
Safe for tender plantsMay 28only 10% chance of frost after
First fall frostOctober 4median — 10% chance by Sep 20
Growing season147 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 25 and returns around October 15.

From the NOAA station Twin Falls Sun Vly Regional Airport, ID, elevation 4,150 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in Twin Falls

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 28 – Apr 11
SpinachSow outdoors · Mar 28 – Apr 18
Broccoli, cabbageStart indoors · Feb 28 – Mar 14
Broccoli, cabbageTransplant · Apr 18 – May 2
Onion setsPlant outdoors · Apr 11 – Apr 25
PotatoesPlant outdoors · Apr 18 – May 2
LettuceSow outdoors · Apr 11 – Apr 25
Carrots, beetsSow outdoors · Apr 18 – May 2
TomatoesStart indoors · Mar 14 – Mar 28
TomatoesTransplant · May 16 – May 30
Peppers, eggplantStart indoors · Feb 28 – Mar 14
Peppers, eggplantTransplant · May 23 – Jun 6
BeansSow outdoors · May 16 – May 30
Sweet cornSow outdoors · May 16 – May 30
Cucumbers, squashSow outdoors · May 16 – May 30
Fall lettuce, spinachSow outdoors · Aug 9 – Aug 23
GarlicPlant cloves · Sep 20 – Oct 25
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 9) and first fall frost (Oct 4) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 83303 came on Mar 4 — 21 days earlier than the 1991–2020 average (Mar 25).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 6b in Idaho

570 plants native to the lower 48 states, recorded in Idaho, and rated by the USDA to survive −5 °F or colder — the bottom of zone 6b. Each links to its USDA PLANTS profile.

Trees 30

balsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °Fblue spruce100 ft · blooms late spring · medium shade tolerance · to −38 °Fboxelder60 ft · blooms early spring · low shade tolerance · to −46 °FDouglas-fir200 ft · blooms mid spring · medium shade tolerance · to −33 °FEngelmann spruce120 ft · blooms late spring · low shade tolerance · to −50 °F

Shrubs 98

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °Falderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °Fantelope bitterbrush6 ft · blooms early spring · medium shade tolerance · to −36 °FBarclay's willow15 ft · high shade tolerance · to −43 °Fbeaked hazelnut15 ft · blooms early spring · low shade tolerance · to −47 °F

Wildflowers & perennials 276

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °F

Grasses 154

Alaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °Falkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °FAlpine Meadow-Foxtail0.5 ft · blooms mid spring · medium shade tolerance · to −33 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Fanalogue sedge1.5 ft · blooms late spring · medium shade tolerance · to −38 °F

Vines 1

western white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Twin Falls, ID.

Soil in Twin Falls, ID

The soil mapped at the center of ZIP 83303 is Portneuf — silt loam, well drained.

TextureSilt loama good balance for most vegetables
pH7.9alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupCwater soaks in slowly
Farmland classPrime farmland if irrigated and reclaimed of excess salts and sodiumUSDA classification

Map unit: Portneuf silt loam, 0 to 2 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 83303; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Twin Falls, ID

Summer high92 °Faverage high, July
Winter low22 °Faverage low, January
Hot days46days a year at 90 °F or more
Freezing nights140nights a year at 32 °F or less
Growing degree days2,921base 50 °F — the season’s usable heat
Longest day15 h 18 mindaylight on June 21
Shortest day9 h 04 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation9.2 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 40 °F, low 22 °F 40°22° JanFebruary: average high 46 °F, low 25 °F 46°25° FebMarch: average high 56 °F, low 32 °F 56°32° MarApril: average high 63 °F, low 36 °F 63°36° AprMay: average high 73 °F, low 45 °F 73°45° MayJune: average high 81 °F, low 52 °F 81°52° JunJuly: average high 92 °F, low 58 °F 92°58° JulAugust: average high 91 °F, low 56 °F 91°56° AugSeptember: average high 80 °F, low 47 °F 80°47° SepOctober: average high 67 °F, low 37 °F 67°37° OctNovember: average high 51 °F, low 28 °F 51°28° NovDecember: average high 40 °F, low 23 °F 40°23° Dec

Precipitation by month inches

0″1″2″January: 1.04 in precipitation 1.0 JanFebruary: 0.78 in precipitation 0.8 FebMarch: 0.87 in precipitation 0.9 MarApril: 1.02 in precipitation 1.0 AprMay: 1.22 in precipitation 1.2 MayJune: 0.67 in precipitation 0.7 JunJuly: 0.16 in precipitation 0.2 JulAugust: 0.34 in precipitation 0.3 AugSeptember: 0.33 in precipitation 0.3 SepOctober: 0.70 in precipitation 0.7 OctNovember: 0.76 in precipitation 0.8 NovDecember: 1.31 in precipitation 1.3 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Twin Falls-Kmvt, ID (within 1 mile); precipitation: Twin Falls-Kmvt, ID (within 1 mile). Daylight is calculated from latitude.

ZIP codes in Twin Falls

833016b
−5 to 0 °F
833036b
−5 to 0 °F

Idaho planting zones →

Questions about Twin Falls

What planting zone is Twin Falls, ID?

Twin Falls, ID is in USDA hardiness zone 6b on the 2023 map (6b: −5 to 0 °F).

When is the last frost in Twin Falls, ID?

The median last spring frost is May 9 and the median first fall frost is October 4 (NOAA 1991–2020 normals, Twin Falls Sun Vly Regional Airport station).

When can I plant a garden in Twin Falls, ID?

Cool-season crops like peas and spinach go in around Mar 28 – Apr 18; tomatoes, peppers, beans and squash after about May 16, once frost risk has passed.

What kind of onions grow in Twin Falls, ID?

Long-day onions: the longest day is 15 h 18 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

How much rain and snow does Twin Falls, ID get?

About 9.2 inches of precipitation a year (NOAA 1991–2020 normals).