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

Planting zone for 83251 — Mackay, ID

ZIP code 83251 (Mackay, Custer County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is June 14 and the first fall frost September 8.

Where ZIP 83251 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.

Zone5a−20 to −15 °F

Coldest night−28.9 to −26.1 °C

Last frostJun 14

First frostSep 8

2012 zone5a

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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Mackay, 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 Mackay, ID

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 14median — 50% chance of a later frost

Safe for tender plantsJune 30only 10% chance of frost after

First fall frostSeptember 8median — 10% chance by Aug 26

Growing season86 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 24 and returns around September 20.

From the NOAA station Chilly Barton Flat, ID — 6 miles away, elevation 6,260 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 83251

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · May 3 – May 17

SpinachSow outdoors · May 3 – May 24

Broccoli, cabbageStart indoors · Apr 5 – Apr 19

Broccoli, cabbageTransplant · May 24 – Jun 7

Onion setsPlant outdoors · May 17 – May 31

PotatoesPlant outdoors · May 24 – Jun 7

LettuceSow outdoors · May 17 – May 31

Carrots, beetsSow outdoors · May 24 – Jun 7

TomatoesStart indoors · Apr 19 – May 3

TomatoesTransplant · Jun 21 – Jul 5

Peppers, eggplantStart indoors · Apr 5 – Apr 19

Peppers, eggplantTransplant · Jun 28 – Jul 12

BeansSow outdoors · Jun 21 – Jul 5

Sweet cornSow outdoors · Jun 21 – Jul 5

Cucumbers, squashSow outdoors · Jun 21 – Jul 5

Fall lettuce, spinachSow outdoors · Jul 14 – Jul 28

GarlicPlant cloves · Aug 25 – Sep 29

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 14) and first fall frost (Sep 8) 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 83251 came on Apr 28 — 22 days earlier than the 1991–2020 average (May 20).

average
May 202026
Apr 28

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 Mackay, ID

The soil mapped at the center of ZIP 83251 is Arrowpeak — gravelly loam, well drained.

TextureGravelly loama good balance for most vegetables

pH6.2slightly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2%moderate

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Arrowpeak-Parkalley, very stony surface, families, complex, 12 to 70 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 83251; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mackay, ID

Summer high82 °Faverage high, July

Winter low7 °Faverage low, January

Hot days5days a year at 90 °F or more

Freezing nights217nights a year at 32 °F or less

Growing degree days1,327base 50 °F — the season’s usable heat

Longest day15 h 29 mindaylight on June 21

Shortest day8 h 53 mindaylight on December 21

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

Precipitation8 inper year, rain and melted snow

Snowfall18 inper year; 79 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Chilly Barton Flat, ID (6 mi away); precipitation: Chilly Barton Flat, ID (6 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.

833535b

Sun Valley, ID · 26 mi

833545b

Sun Valley, ID · 27 mi

Idaho planting zones →

Questions about 83251

What planting zone is ZIP code 83251?

ZIP code 83251 (Mackay, ID) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Mackay, ID?

The median last spring frost (32 °F) near 83251 is June 14; after June 30 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Chilly Barton Flat station.

When is the first frost in Mackay, ID?

The median first fall frost near 83251 is September 8, giving a median frost-free growing season of 86 days.

When should I plant tomatoes in 83251?

Start tomato seeds indoors around Apr 19 – May 3 and set transplants outside around Jun 21 – Jul 5, one to three weeks after the median last frost.

How much rain and snow does 83251 get?

About 8 inches of precipitation a year and 18 inches of snowfall (NOAA 1991–2020 normals, Chilly Barton Flat station).

How hot do summers get in Mackay, ID?

The average high peaks at 82 °F in July, with about 5 days a year at 90 °F or more.

What kind of soil does 83251 have?

The USDA soil survey maps Arrowpeak at the center of ZIP 83251: gravelly loam, well drained, pH about 6.2 (slightly acidic).

Did spring come early in Mackay, ID in 2026?

Spring leaf-out near 83251 came on Apr 28 in 2026, 22 days earlier than the 1991–2020 average (May 20), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Mackay, ID?

Long-day onions: the longest day near 83251 is 15 h 29 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).