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

Planting zone for 57730 — Custer, SD

ZIP code 57730 (Custer, Custer County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 23 and the first fall frost September 24.

Where ZIP 57730 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 frostMay 23

First frostSep 24

2012 zone4b

Was 4b 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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Custer, 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 Custer, SD

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 23median — 50% chance of a later frost

Safe for tender plantsJune 6only 10% chance of frost after

First fall frostSeptember 24median — 10% chance by Sep 9

Growing season122 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 10 and returns around October 5.

From the NOAA station Custer Co. Airport, SD — 2 miles away, elevation 5,545 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 57730

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 11 – Apr 25

SpinachSow outdoors · Apr 11 – May 2

Broccoli, cabbageStart indoors · Mar 14 – Mar 28

Broccoli, cabbageTransplant · May 2 – May 16

Onion setsPlant outdoors · Apr 25 – May 9

PotatoesPlant outdoors · May 2 – May 16

LettuceSow outdoors · Apr 25 – May 9

Carrots, beetsSow outdoors · May 2 – May 16

TomatoesStart indoors · Mar 28 – Apr 11

TomatoesTransplant · May 30 – Jun 13

Peppers, eggplantStart indoors · Mar 14 – Mar 28

Peppers, eggplantTransplant · Jun 6 – Jun 20

BeansSow outdoors · May 30 – Jun 13

Sweet cornSow outdoors · May 30 – Jun 13

Cucumbers, squashSow outdoors · May 30 – Jun 13

Fall lettuce, spinachSow outdoors · Jul 30 – Aug 13

GarlicPlant cloves · Sep 10 – Oct 15

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 23) and first fall frost (Sep 24) 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 57730 came on Mar 24 — 27 days earlier than the 1991–2020 average (Apr 20).

average
Apr 202026
Mar 24

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 5a in South Dakota

452 plants native to the lower 48 states, recorded in South Dakota, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. 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 Custer, SD.

Soil in Custer, SD

The soil mapped at the center of ZIP 57730 is Buska — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH5.2strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter70%high

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Buska-Virkula, high mica loams, dry, 2 to 15 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 57730; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Custer, SD

Summer high79 °Faverage high, July

Winter low15 °Faverage low, January

Hot days6days a year at 90 °F or more

Freezing nights195nights a year at 32 °F or less

Growing degree days1,624base 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)

Precipitation19.8 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: Custer Co. Airport, SD (2 mi away); precipitation: Custer Co. Airport, SD (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Hill City, SD · 21 mi

577025a

Rapid City, SD · 24 mi

577385a

Fairburn, SD · 25 mi

577475a

Hot Springs, SD · 25 mi

577095b

Rapid City, SD · 29 mi

577445a

Hermosa, SD · 31 mi

South Dakota planting zones →

Questions about 57730

What planting zone is ZIP code 57730?

ZIP code 57730 (Custer, SD) 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 Custer, SD?

The median last spring frost (32 °F) near 57730 is May 23; after June 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Custer Co. Airport station.

When is the first frost in Custer, SD?

The median first fall frost near 57730 is September 24, giving a median frost-free growing season of 122 days.

When should I plant tomatoes in 57730?

Start tomato seeds indoors around Mar 28 – Apr 11 and set transplants outside around May 30 – Jun 13, one to three weeks after the median last frost.

How much rain and snow does 57730 get?

About 19.8 inches of precipitation a year (NOAA 1991–2020 normals, Custer Co. Airport station).

How hot do summers get in Custer, SD?

The average high peaks at 79 °F in July, with about 6 days a year at 90 °F or more.

What kind of soil does 57730 have?

The USDA soil survey maps Buska at the center of ZIP 57730: slightly decomposed plant material, well drained, pH about 5.2 (strongly acidic).

Did spring come early in Custer, SD in 2026?

Spring leaf-out near 57730 came on Mar 24 in 2026, 27 days earlier than the 1991–2020 average (Apr 20), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Custer, SD?

Long-day onions: the longest day near 57730 is 15 h 27 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 57730 change?

Yes. The 2012 USDA map put 57730 in zone 4b; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.