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

Planting zone for 57440 — Frankfort, SD

ZIP code 57440 (Frankfort, Spink County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 8 and the first fall frost October 1.

Where ZIP 57440 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 8

First frostOct 1

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 Frankfort, 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 Frankfort, SD

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 8median — 50% chance of a later frost

Safe for tender plantsMay 21only 10% chance of frost after

First fall frostOctober 1median — 10% chance by Sep 19

Growing season145 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 29 and returns around October 8.

From the NOAA station Redfield, SD — 13 miles away, elevation 1,309 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 57440

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 27 – Apr 10

SpinachSow outdoors · Mar 27 – Apr 17

Broccoli, cabbageStart indoors · Feb 27 – Mar 13

Broccoli, cabbageTransplant · Apr 17 – May 1

Onion setsPlant outdoors · Apr 10 – Apr 24

PotatoesPlant outdoors · Apr 17 – May 1

LettuceSow outdoors · Apr 10 – Apr 24

Carrots, beetsSow outdoors · Apr 17 – May 1

TomatoesStart indoors · Mar 13 – Mar 27

TomatoesTransplant · May 15 – May 29

Peppers, eggplantStart indoors · Feb 27 – Mar 13

Peppers, eggplantTransplant · May 22 – Jun 5

BeansSow outdoors · May 15 – May 29

Sweet cornSow outdoors · May 15 – May 29

Cucumbers, squashSow outdoors · May 15 – May 29

Fall lettuce, spinachSow outdoors · Aug 6 – Aug 20

GarlicPlant cloves · Sep 17 – Oct 22

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 8) and first fall frost (Oct 1) 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 57440 came on Apr 8 — 8 days earlier than the 1991–2020 average (Apr 16).

average
Apr 162026
Apr 8

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 Frankfort, SD.

Soil in Frankfort, SD

The soil mapped at the center of ZIP 57440 is Harmony — silty clay loam, moderately well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up

pH6.7neutral; most vegetables like 6.0–7.0

DrainageModerately well drainednatural drainage class

Organic matter6%high

Hydrologic groupCwater soaks in slowly

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Harmony-Aberdeen silty clay loams, 0 to 2 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 57440; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Frankfort, SD

Summer high84 °Faverage high, July

Winter low3 °Faverage low, January

Hot days17days a year at 90 °F or more

Freezing nights179nights a year at 32 °F or less

Growing degree days2,534base 50 °F — the season’s usable heat

Longest day15 h 36 mindaylight on June 21

Shortest day8 h 47 mindaylight on December 21

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

Precipitation22.3 inper year, rain and melted snow

Snowfall23 inper year

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Redfield, SD (13 mi away); precipitation: Doland, SD (8 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Hitchcock, SD · 17 mi

Brentford, SD · 21 mi

574614a

Mellette, SD · 23 mi

South Dakota planting zones →

Questions about 57440

What planting zone is ZIP code 57440?

ZIP code 57440 (Frankfort, 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 Frankfort, SD?

The median last spring frost (32 °F) near 57440 is May 8; after May 21 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Redfield station.

When is the first frost in Frankfort, SD?

The median first fall frost near 57440 is October 1, giving a median frost-free growing season of 145 days.

When should I plant tomatoes in 57440?

Start tomato seeds indoors around Mar 13 – Mar 27 and set transplants outside around May 15 – May 29, one to three weeks after the median last frost.

How much rain and snow does 57440 get?

About 22.3 inches of precipitation a year and 23 inches of snowfall (NOAA 1991–2020 normals, Doland station).

How hot do summers get in Frankfort, SD?

The average high peaks at 84 °F in July, with about 17 days a year at 90 °F or more.

What kind of soil does 57440 have?

The USDA soil survey maps Harmony at the center of ZIP 57440: silty clay loam, moderately well drained, pH about 6.7 (neutral).

Did spring come early in Frankfort, SD in 2026?

Spring leaf-out near 57440 came on Apr 8 in 2026, 8 days earlier than the 1991–2020 average (Apr 16), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Frankfort, SD?

Long-day onions: the longest day near 57440 is 15 h 36 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 57440 change?

Yes. The 2012 USDA map put 57440 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.