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

Planting zone for 57481 — Westport, SD

ZIP code 57481 (Westport, Brown 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 28.

Where ZIP 57481 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 28

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 Westport, 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 Westport, 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 21only 10% chance of frost after

First fall frostSeptember 28median — 10% chance by Sep 17

Growing season141 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 1 and returns around October 6.

From the NOAA station Leola, SD — 13 miles away, elevation 1,581 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 57481

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 3 – Aug 17

GarlicPlant cloves · Sep 14 – Oct 19

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 9) and first fall frost (Sep 28) 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 57481 came on Apr 16 — 3 days earlier than the 1991–2020 average (Apr 19).

average
Apr 192026
Apr 16

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 Westport, SD.

Soil in Westport, SD

The soil mapped at the center of ZIP 57481 is Niobell — loam, moderately well drained.

TextureLoama good balance for most vegetables

pH6.6neutral; most vegetables like 6.0–7.0

DrainageModerately well drainednatural drainage class

Organic matter4%moderate

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Niobell-Noonan loams, 3 to 6 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 57481; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Westport, SD

Summer high83 °Faverage high, July

Winter low1 °Faverage low, January

Hot days16days a year at 90 °F or more

Freezing nights175nights a year at 32 °F or less

Growing degree days2,278base 50 °F — the season’s usable heat

Longest day15 h 42 mindaylight on June 21

Shortest day8 h 41 mindaylight on December 21

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

Precipitation21.7 inper year, rain and melted snow

Snowfall44 inper year; 75 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: Leola, SD (13 mi away); precipitation: Westport 2 Nw, SD (7 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

574264a

Barnard, SD · 10 mi

574414b

Frederick, SD · 14 mi

South Dakota planting zones →

Questions about 57481

What planting zone is ZIP code 57481?

ZIP code 57481 (Westport, 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 Westport, SD?

The median last spring frost (32 °F) near 57481 is May 9; after May 21 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Leola station.

When is the first frost in Westport, SD?

The median first fall frost near 57481 is September 28, giving a median frost-free growing season of 141 days.

When should I plant tomatoes in 57481?

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 57481 get?

About 21.7 inches of precipitation a year and 44 inches of snowfall (NOAA 1991–2020 normals, Westport 2 Nw station).

How hot do summers get in Westport, SD?

The average high peaks at 83 °F in July, with about 16 days a year at 90 °F or more.

What kind of soil does 57481 have?

The USDA soil survey maps Niobell at the center of ZIP 57481: loam, moderately well drained, pH about 6.6 (neutral).

Did spring come early in Westport, SD in 2026?

Spring leaf-out near 57481 came on Apr 16 in 2026, 3 days earlier than the 1991–2020 average (Apr 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Westport, SD?

Long-day onions: the longest day near 57481 is 15 h 42 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 57481 change?

Yes. The 2012 USDA map put 57481 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.