Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 83281 — Swanlake, ID

ZIP code 83281 (Swanlake, Bannock County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 31 and the first fall frost September 18.

Where ZIP 83281 is

Outlined: the ZIP code area · 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.

Zone5b−15 to −10 °F

Coldest night−26.1 to −23.3 °C

Last frostMay 31

First frostSep 18

2012 zone5b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Swanlake, ID…

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 Swanlake, ID

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMay 31median — 50% chance of a later frost

Safe for tender plantsJune 16only 10% chance of frost after

First fall frostSeptember 18median — 10% chance by Sep 3

Growing season110 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 9 and returns around October 1.

From the NOAA station Downey, ID — 12 miles away, elevation 4,866 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 83281

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 19 – May 3

SpinachSow outdoors · Apr 19 – May 10

Broccoli, cabbageStart indoors · Mar 22 – Apr 5

Broccoli, cabbageTransplant · May 10 – May 24

Onion setsPlant outdoors · May 3 – May 17

PotatoesPlant outdoors · May 10 – May 24

LettuceSow outdoors · May 3 – May 17

Carrots, beetsSow outdoors · May 10 – May 24

TomatoesStart indoors · Apr 5 – Apr 19

TomatoesTransplant · Jun 7 – Jun 21

Peppers, eggplantStart indoors · Mar 22 – Apr 5

Peppers, eggplantTransplant · Jun 14 – Jun 28

BeansSow outdoors · Jun 7 – Jun 21

Sweet cornSow outdoors · Jun 7 – Jun 21

Cucumbers, squashSow outdoors · Jun 7 – Jun 21

Fall lettuce, spinachSow outdoors · Jul 24 – Aug 7

GarlicPlant cloves · Sep 4 – Oct 9

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 31) and first fall frost (Sep 18) 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 83281 came on Mar 23 — 22 days earlier than the 1991–2020 average (Apr 14).

average
Apr 142026
Mar 23

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).

Soil in Swanlake, ID

The soil mapped at the center of ZIP 83281 is Bancroft — silt loam, well drained.

TextureSilt loama good balance for most vegetables

pH6.7neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2.5%moderate

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Bancroft silt loam, 4 to 12 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 83281; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Swanlake, ID

Summer high89 °Faverage high, July

Winter low14 °Faverage low, January

Hot days37days a year at 90 °F or more

Freezing nights180nights a year at 32 °F or less

Growing degree days2,011base 50 °F — the season’s usable heat

Longest day15 h 17 mindaylight on June 21

Shortest day9 h 05 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation27.1 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Downey, ID (12 mi away); precipitation: Oxford Spring, ID (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

7 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

Lava Hot Springs, ID · 21 mi

Idaho planting zones →

Questions about 83281

What planting zone is ZIP code 83281?

ZIP code 83281 (Swanlake, ID) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Swanlake, ID?

The median last spring frost (32 °F) near 83281 is May 31; after June 16 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Downey station.

When is the first frost in Swanlake, ID?

The median first fall frost near 83281 is September 18, giving a median frost-free growing season of 110 days.

When should I plant tomatoes in 83281?

Start tomato seeds indoors around Apr 5 – Apr 19 and set transplants outside around Jun 7 – Jun 21, one to three weeks after the median last frost.

How much rain and snow does 83281 get?

About 27.1 inches of precipitation a year (NOAA 1991–2020 normals, Oxford Spring station).

How hot do summers get in Swanlake, ID?

The average high peaks at 89 °F in July, with about 37 days a year at 90 °F or more.

What kind of soil does 83281 have?

The USDA soil survey maps Bancroft at the center of ZIP 83281: silt loam, well drained, pH about 6.7 (neutral).

Did spring come early in Swanlake, ID in 2026?

Spring leaf-out near 83281 came on Mar 23 in 2026, 22 days earlier than the 1991–2020 average (Apr 14), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Swanlake, ID?

Long-day onions: the longest day near 83281 is 15 h 17 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).