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

Planting zone for 57633 — Isabel, SD

ZIP code 57633 (Isabel, Dewey County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 11 and the first fall frost September 30.

Where ZIP 57633 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 11

First frostSep 30

2012 zone4b

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 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Isabel, 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 Isabel, SD

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 11median — 50% chance of a later frost

Safe for tender plantsMay 24only 10% chance of frost after

First fall frostSeptember 30median — 10% chance by Sep 16

Growing season140 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 2 and returns around October 7.

From the NOAA station Glad Valley 2 W, SD — 14 miles away, elevation 2,487 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 57633

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 30 – Apr 13

SpinachSow outdoors · Mar 30 – Apr 20

Broccoli, cabbageStart indoors · Mar 2 – Mar 16

Broccoli, cabbageTransplant · Apr 20 – May 4

Onion setsPlant outdoors · Apr 13 – Apr 27

PotatoesPlant outdoors · Apr 20 – May 4

LettuceSow outdoors · Apr 13 – Apr 27

Carrots, beetsSow outdoors · Apr 20 – May 4

TomatoesStart indoors · Mar 16 – Mar 30

TomatoesTransplant · May 18 – Jun 1

Peppers, eggplantStart indoors · Mar 2 – Mar 16

Peppers, eggplantTransplant · May 25 – Jun 8

BeansSow outdoors · May 18 – Jun 1

Sweet cornSow outdoors · May 18 – Jun 1

Cucumbers, squashSow outdoors · May 18 – Jun 1

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 11) 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 57633 came on Mar 24 — 21 days earlier than the 1991–2020 average (Apr 14).

average
Apr 142026
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 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 Isabel, SD.

Soil in Isabel, SD

The soil mapped at the center of ZIP 57633 is Vebar — fine sandy loam, well drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding

pH7.0neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2.5%moderate

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Vebar-Daglum complex, 3 to 9 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 57633; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Isabel, SD

Summer high84 °Faverage high, July

Winter low7 °Faverage low, January

Hot days21days a year at 90 °F or more

Freezing nights181nights a year at 32 °F or less

Growing degree days2,370base 50 °F — the season’s usable heat

Longest day15 h 41 mindaylight on June 21

Shortest day8 h 42 mindaylight on December 21

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

Precipitation19.4 inper year, rain and melted snow

Snowfall47 inper year

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Glad Valley 2 W, SD (14 mi away); precipitation: Glad Valley 2 W, SD (14 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 4b.

576564b

Timber Lake, SD · 21 mi

Mc Intosh, SD · 33 mi

South Dakota planting zones →

Questions about 57633

What planting zone is ZIP code 57633?

ZIP code 57633 (Isabel, 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 Isabel, SD?

The median last spring frost (32 °F) near 57633 is May 11; after May 24 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Glad Valley 2 W station.

When is the first frost in Isabel, SD?

The median first fall frost near 57633 is September 30, giving a median frost-free growing season of 140 days.

When should I plant tomatoes in 57633?

Start tomato seeds indoors around Mar 16 – Mar 30 and set transplants outside around May 18 – Jun 1, one to three weeks after the median last frost.

How much rain and snow does 57633 get?

About 19.4 inches of precipitation a year and 47 inches of snowfall (NOAA 1991–2020 normals, Glad Valley 2 W station).

How hot do summers get in Isabel, SD?

The average high peaks at 84 °F in July, with about 21 days a year at 90 °F or more.

What kind of soil does 57633 have?

The USDA soil survey maps Vebar at the center of ZIP 57633: fine sandy loam, well drained, pH about 7.0 (neutral).

Did spring come early in Isabel, SD in 2026?

Spring leaf-out near 57633 came on Mar 24 in 2026, 21 days earlier than the 1991–2020 average (Apr 14), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Isabel, SD?

Long-day onions: the longest day near 57633 is 15 h 41 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).