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

Planting zone for 57621 — Bullhead, SD

ZIP code 57621 (Bullhead, Corson County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 9 and the first fall frost September 30.

Where ZIP 57621 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.

Zone4b−25 to −20 °F

Coldest night−31.7 to −28.9 °C

Last frostMay 9

First frostSep 30

2012 zone4a

Was 4a on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Bullhead, SD…

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 Bullhead, SD

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 24only 10% chance of frost after

First fall frostSeptember 30median — 10% chance by Sep 19

Growing season143 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 30 and returns around October 7.

From the NOAA station Mc Intosh 6 Se, SD — 11 miles away, elevation 2,179 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 57621

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 5 – Aug 19

GarlicPlant cloves · Sep 16 – Oct 21

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 9) and first fall frost (Sep 30) 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 57621 came on Apr 7 — 9 days earlier than the 1991–2020 average (Apr 16).

average
Apr 162026
Apr 7

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 4b in South Dakota

430 plants native to the lower 48 states, recorded in South Dakota, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

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 Bullhead, SD.

Soil in Bullhead, SD

The soil mapped at the center of ZIP 57621 is Korchea — loam, well drained.

TextureLoama good balance for most vegetables

pH7.5slightly alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2.5%moderate

Hydrologic groupBwater soaks in moderately

Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Korchea loam.

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 57621; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Bullhead, SD

Summer high86 °Faverage high, July

Winter low7 °Faverage low, January

Hot days27days a year at 90 °F or more

Freezing nights176nights a year at 32 °F or less

Growing degree days2,558base 50 °F — the season’s usable heat

Longest day15 h 43 mindaylight on June 21

Shortest day8 h 40 mindaylight on December 21

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

Precipitation17.3 inper year, rain and melted snow

Snowfall43 inper year; 89 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: Mc Intosh 6 Se, SD (11 mi away); precipitation: Mc Intosh 6 Se, SD (11 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

576594b

Walker, SD · 8 mi

576414b

Mc Intosh, SD · 14 mi

576394a

Little Eagle, SD · 15 mi

576424b

Mc Laughlin, SD · 18 mi

576604b

Watauga, SD · 22 mi

576574b

Trail City, SD · 22 mi

585684b

Selfridge, ND · 23 mi

576564b

Timber Lake, SD · 24 mi

South Dakota planting zones →

Questions about 57621

What planting zone is ZIP code 57621?

ZIP code 57621 (Bullhead, SD) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in Bullhead, SD?

The median last spring frost (32 °F) near 57621 is May 9; after May 24 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mc Intosh 6 Se station.

When is the first frost in Bullhead, SD?

The median first fall frost near 57621 is September 30, giving a median frost-free growing season of 143 days.

When should I plant tomatoes in 57621?

Start tomato seeds indoors around Mar 14 – Mar 28 and set transplants outside around May 16 – May 30, one to three weeks after the median last frost.

How much rain and snow does 57621 get?

About 17.3 inches of precipitation a year and 43 inches of snowfall (NOAA 1991–2020 normals, Mc Intosh 6 Se station).

How hot do summers get in Bullhead, SD?

The average high peaks at 86 °F in July, with about 27 days a year at 90 °F or more.

What kind of soil does 57621 have?

The USDA soil survey maps Korchea at the center of ZIP 57621: loam, well drained, pH about 7.5 (slightly alkaline).

Did spring come early in Bullhead, SD in 2026?

Spring leaf-out near 57621 came on Apr 7 in 2026, 9 days earlier than the 1991–2020 average (Apr 16), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Bullhead, SD?

Long-day onions: the longest day near 57621 is 15 h 43 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 57621 change?

Yes. The 2012 USDA map put 57621 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.