What does USDA hardiness zone 4a mean in South Dakota?

Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 11 locations in South Dakota fall in this zone. It does not set planting dates; see the frost calendar below for that.

Where in South Dakota's zone 4a is the growing season longest?

Lake runs the longest season on this page at about 160 days; Sunset Colony is shortest at about 135 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.

When should I plant tomatoes in South Dakota's zone 4a?

Using Castlewood's frost dates (this page's median-season location): start seeds indoors about Mar 15 – Mar 29, then transplant outside about May 17 – May 24. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.

Does every location in South Dakota's zone 4a have the same frost dates?

No — they do not all share a weather station, so frost dates vary by a week or more across the 11 locations listed (see the table above for each location's own dates).

USDA zone 4a in South Dakota

−30 to −25 °F avg. annual extreme minimum · 11 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 4a covers 11 locations across South Dakota (average annual extreme minimum −30 to −25 °F): Aberdeen, SD, Castlewood, SD, Chelsea, SD, Columbia, SD, Conde, SD, Ferney, SD, and 5 more. Average last spring frost across this group ranges May 2 (Lake) to May 14 (Summit), and growing seasons run 135–160 days (Sunset Colony to Lake) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every South Dakota location's own frost dates; the printable planting calendar uses Castlewood, this group's median-season location.

USDA zone: 4a−30 to −25 °F
Last frost range: May 2–May 14avg, 32°F
First frost range: Sep 26–Oct 9avg, 32°F
Growing season range: 135–160days

Locations in this group

Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.

Own frost dates per location.
Location	Also covers	Nearest station	Last frost	First frost	Season (days)
Aberdeen	Groton, Bath, Warner, Stratford	Aberdeen	May 9	Sep 26	139
Castlewood *	—	Castlewood	May 10	Sep 27	139
Chelsea	Mellette, Brentford	Mellette 4 W	May 11	Sep 27	137
Columbia	Hecla, Claremont, Westport	Columbia 8 N	May 7	Sep 29	145
Conde	—	Conde	May 6	Sep 29	144
Ferney	—	Andover #2	May 6	Oct 4	150
Lake	—	Roy Lake	May 2	Oct 9	160
Little Eagle	Fort Yates	Mc Laughlin	May 12	Sep 28	137
Pollock	Strasburg, Hague	Pollock	May 8	Sep 30	143
Summit	—	Summit 1 W	May 14	Sep 28	136
Sunset Colony	Langford, Kidder	Britton	May 13	Sep 26	135

* Castlewood is this group's median-season location — the calendar below is computed from its data.

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.

Planting calendar (Castlewood, representative)

Computed from Castlewood's average frost dates — the median-season location in this South Dakotazone 4a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Castlewood (South Dakota, zone 4a), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 15 – Mar 29	May 17 – May 24	Jul 16 – Aug 5	—	matures comfortably
Pepper	Very tender	Mar 1 – Mar 15	May 24 – May 31	Jul 23 – Aug 22	—	matures comfortably
Cucumber	Tender	Apr 12 – Apr 19	May 17 – May 24	Jul 6 – Jul 26	—	matures comfortably
Summer squash / zucchini	Tender	—	May 17 – May 24	Jul 1 – Jul 16	—	matures comfortably
Bush bean	Tender	—	May 17 – May 24	Jul 6 – Jul 16	Jul 29 – Aug 8	matures comfortably
Sweet corn	Tender	—	May 10 – May 24	Jul 9 – Aug 8	—	matures comfortably
Basil	Very tender	Mar 29 – Apr 12	May 17 – May 24	Jun 16 – Jul 1	—	matures comfortably
Lettuce	Half-hardy	Mar 29 – Apr 12	Apr 12 – Apr 26	May 27 – Jun 11	Jul 15 – Jul 30	matures comfortably
Pea	Hardy	—	Mar 29 – Apr 12	May 23 – Jun 7	Jul 5 – Jul 20	matures comfortably
Spinach	Hardy	—	Mar 29 – Apr 12	May 8 – May 18	Jul 25 – Aug 4	matures comfortably
Carrot	Half-hardy	—	Apr 19 – Apr 26	Jun 18 – Jul 8	Jun 25 – Jul 15	matures comfortably
Broccoli	Half-hardy	Mar 15 – Mar 29	Apr 12 – Apr 26	Jun 6 – Jun 26	Jun 30 – Jul 20	matures comfortably

Which crops fit this growing season

Using Castlewood's own 139-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.

Frost & freeze dates (Castlewood)

From NOAA's 1991–2020 Climate Normals at station USC00391519. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020), Castlewood.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	May 19	Jun 1	Sep 17	Sep 29	120
32°F (freeze)	May 10	May 23	Sep 27	Oct 7	139
28°F	May 1	May 14	Oct 4	Oct 18	156
24°F	Apr 23	May 6	Oct 15	Oct 28	175

Growing degree days

Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 11 locations is 2,436; Castlewood's own reading is shown below.

Annual growing degree days for Castlewood (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	2,157	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	3,923	cool-season crops (brassicas, greens)

Hardiness zone 4a in South Dakota

Zone 4a means an average annual extreme minimum winter temperature of about −30 to −25 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. South Dakota spans 4 hardiness zones in this dataset — see all South Dakota locations for the full range, including zones4b, 5a, 5b.

Explore zone 4a in other states at zone 4a, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 4a mean in South Dakota?: Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 11 locations in South Dakota fall in this zone. It does not set planting dates; see the frost calendar below for that.
Where in South Dakota's zone 4a is the growing season longest?: Lake runs the longest season on this page at about 160 days; Sunset Colony is shortest at about 135 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
When should I plant tomatoes in South Dakota's zone 4a?: Using Castlewood's frost dates (this page's median-season location): start seeds indoors about Mar 15 – Mar 29, then transplant outside about May 17 – May 24. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
Does every location in South Dakota's zone 4a have the same frost dates?: No — they do not all share a weather station, so frost dates vary by a week or more across the 11 locations listed (see the table above for each location's own dates).

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.