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

Planting zone for Caldwell, ID

Caldwell, ID is in USDA zone 7a across its 3 ZIP codes. The median last spring frost is April 29 and the first fall frost October 13.

Caldwell on the zone map

Outlined: its 2 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.

Zone7a0 to 5 °F
ZIP codes3
Last frostApr 29
First frostOct 13
Growing season164 days

7a 3 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 Caldwell, ID

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 29median — 50% chance of a later frost
Safe for tender plantsMay 18only 10% chance of frost after
First fall frostOctober 13median — 10% chance by Sep 29
Growing season164 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 11 and returns around October 25.

From the NOAA station Nampa Sugar Factory, ID, elevation 2,471 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 Caldwell

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 18 – Apr 1
SpinachSow outdoors · Mar 18 – Apr 8
Broccoli, cabbageStart indoors · Feb 18 – Mar 4
Broccoli, cabbageTransplant · Apr 8 – Apr 22
Onion setsPlant outdoors · Apr 1 – Apr 15
PotatoesPlant outdoors · Apr 8 – Apr 22
LettuceSow outdoors · Apr 1 – Apr 15
Carrots, beetsSow outdoors · Apr 8 – Apr 22
TomatoesStart indoors · Mar 4 – Mar 18
TomatoesTransplant · May 6 – May 20
Peppers, eggplantStart indoors · Feb 18 – Mar 4
Peppers, eggplantTransplant · May 13 – May 27
BeansSow outdoors · May 6 – May 20
Sweet cornSow outdoors · May 6 – May 20
Cucumbers, squashSow outdoors · May 6 – May 20
Fall lettuce, spinachSow outdoors · Aug 18 – Sep 1
GarlicPlant cloves · Sep 29 – Nov 3
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 29) and first fall frost (Oct 13) 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 83607 came on Mar 10 — 10 days earlier than the 1991–2020 average (Mar 20).

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 7a in Idaho

575 plants native to the lower 48 states, recorded in Idaho, and rated by the USDA to survive 0 °F or colder — the bottom of zone 7a. 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 101

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 277

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 155

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 Caldwell, ID.

Soil in Caldwell, ID

The soil mapped at the center of ZIP 83607 is Greenleaf — silt loam, well drained.

TextureSilt loama good balance for most vegetables
pH7.5slightly alkaline; 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 irrigatedUSDA classification

Map unit: Greenleaf-Owyhee silt loams, 1 to 3 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 83607; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Caldwell, ID

Summer high90 °Faverage high, July
Winter low24 °Faverage low, December
Hot days41days a year at 90 °F or more
Freezing nights106nights a year at 32 °F or less
Growing degree days2,992base 50 °F — the season’s usable heat
Longest day15 h 27 mindaylight on June 21
Shortest day8 h 55 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation12.3 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 25 °F 40°25° JanFebruary: average high 47 °F, low 27 °F 47°27° FebMarch: average high 58 °F, low 34 °F 58°34° MarApril: average high 65 °F, low 38 °F 65°38° AprMay: average high 73 °F, low 46 °F 73°46° MayJune: average high 81 °F, low 52 °F 81°52° JunJuly: average high 90 °F, low 59 °F 90°59° JulAugust: average high 89 °F, low 57 °F 89°57° AugSeptember: average high 80 °F, low 49 °F 80°49° SepOctober: average high 66 °F, low 39 °F 66°39° OctNovember: average high 50 °F, low 31 °F 50°31° NovDecember: average high 40 °F, low 24 °F 40°24° Dec

Precipitation by month inches

0″1″2″January: 1.41 in precipitation 1.4 JanFebruary: 1.03 in precipitation 1.0 FebMarch: 1.22 in precipitation 1.2 MarApril: 1.23 in precipitation 1.2 AprMay: 1.63 in precipitation 1.6 MayJune: 0.88 in precipitation 0.9 JunJuly: 0.28 in precipitation 0.3 JulAugust: 0.21 in precipitation 0.2 AugSeptember: 0.52 in precipitation 0.5 SepOctober: 0.84 in precipitation 0.8 OctNovember: 1.17 in precipitation 1.2 NovDecember: 1.91 in precipitation 1.9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Deer Flat Dam, ID (9 mi away); precipitation: Middleton 0.7 Ene, ID (6 mi away). Daylight is calculated from latitude.

ZIP codes in Caldwell

836057a
0 to 5 °F
836067a
0 to 5 °F
836077a
0 to 5 °F

Idaho planting zones →

Questions about Caldwell

What planting zone is Caldwell, ID?

Caldwell, ID is in USDA hardiness zone 7a on the 2023 map (7a: 0 to 5 °F).

When is the last frost in Caldwell, ID?

The median last spring frost is April 29 and the median first fall frost is October 13 (NOAA 1991–2020 normals, Nampa Sugar Factory station).

When can I plant a garden in Caldwell, ID?

Cool-season crops like peas and spinach go in around Mar 18 – Apr 8; tomatoes, peppers, beans and squash after about May 6, once frost risk has passed.

What kind of onions grow in Caldwell, ID?

Long-day onions: the longest day is 15 h 27 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

How much rain and snow does Caldwell, ID get?

About 12.3 inches of precipitation a year (NOAA 1991–2020 normals).