What does USDA hardiness zone 4b mean in North Dakota?

Zone 4b means an average annual extreme minimum winter temperature of −25 to −20 °F — the standard USDA measure of which perennials survive winter. 24 locations in North Dakota fall in this zone. It does not set planting dates; see the frost calendar below for that.

Where in North Dakota's zone 4b is the growing season longest?

Lidgerwood runs the longest season on this page at about 157 days; Hettinger is shortest at about 103 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 North Dakota's zone 4b?

Using LaMoure'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 North Dakota's zone 4b 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 24 locations listed (see the table above for each location's own dates).

USDA zone 4b in North Dakota

−25 to −20 °F avg. annual extreme minimum · 24 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 4b covers 24 locations across North Dakota (average annual extreme minimum −25 to −20 °F): Amidon, ND, Ashley, ND, Belfield, ND, Bowman, ND, Cayuga, ND, Dickinson, ND, and 18 more. Average last spring frost across this group ranges May 2 (Lidgerwood) to May 30 (Hettinger), and growing seasons run 103–157 days (Hettinger to Lidgerwood) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every North Dakota location's own frost dates; the printable planting calendar uses LaMoure, this group's median-season location.

USDA zone: 4b−25 to −20 °F
Last frost range: May 2–May 30avg, 32°F
First frost range: Sep 11–Oct 6avg, 32°F
Growing season range: 103–157days

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)
Amidon	—	Amidon	May 12	Sep 29	136
Ashley	Long Lake, Fredonia, Lehr	Ashley	May 13	Sep 28	137
Belfield	—	Medora 7 E	May 9	Sep 30	142
Bowman	Rhame, Gascoyne	Bowman	May 16	Sep 25	132
Cayuga	—	Forman 5 Sse	May 7	Oct 1	146
Dickinson	—	Dickinson	May 20	Sep 22	123
Edgeley	Kulm	Edgeley 3wnw	May 7	Oct 2	148
Ellendale	Forbes	Ellendale	May 4	Oct 2	149
Fullerton	—	Fullerton 1 Ese	May 9	Sep 28	141
Gascoyne	—	Ludlow 3 Sse	May 16	Sep 26	131
Gladstone	—	Richardton Abbey	May 9	Oct 1	145
Golva	—	Carlyle 13 Nw	May 18	Sep 29	134
Hankinson	Rosholt, New Effington	Victor 4 N	May 4	Oct 3	152
Hettinger	Reeder	Hettinger Muni Ap	May 24	Sep 18	115
Hettinger	—	Lodgepole 5sw	May 30	Sep 11	103
Jamestown	Cleveland, Montpelier	Jamestown State Hosp	May 8	Sep 29	143
Jamestown	Buchanan	Jamestown Muni Ap	May 11	Sep 28	138
Jud	—	Gackle	May 6	Oct 4	150
LaMoure *	Marion, Dickey, Berlin	La Moure	May 10	Sep 28	140
Lidgerwood	—	Lidgerwood	May 2	Oct 6	157
McClusky	—	Mc Clusky	May 8	Oct 1	145
New England	—	New England	May 16	Sep 24	128
Reeder	—	Ralph 1 N	May 18	Sep 23	126
South Heart	—	Theodore Roosevelt Ap	May 18	Sep 25	129

* LaMoure 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 (LaMoure, representative)

Computed from LaMoure's average frost dates — the median-season location in this North Dakotazone 4b 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 LaMoure (North Dakota, zone 4b), 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 30 – Aug 9	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 16 – Jul 31	matures comfortably
Pea	Hardy	—	Mar 29 – Apr 12	May 23 – Jun 7	Jul 6 – Jul 21	matures comfortably
Spinach	Hardy	—	Mar 29 – Apr 12	May 8 – May 18	Jul 26 – Aug 5	matures comfortably
Carrot	Half-hardy	—	Apr 19 – Apr 26	Jun 18 – Jul 8	Jun 26 – Jul 16	matures comfortably
Broccoli	Half-hardy	Mar 15 – Mar 29	Apr 12 – Apr 26	Jun 6 – Jun 26	Jul 1 – Jul 21	matures comfortably

Which crops fit this growing season

Using LaMoure's own 140-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 (LaMoure)

From NOAA's 1991–2020 Climate Normals at station USC00324937. 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), LaMoure.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	May 20	Jun 2	Sep 20	Oct 1	122
32°F (freeze)	May 10	May 22	Sep 28	Oct 10	140
28°F	May 1	May 14	Oct 6	Oct 19	157
24°F	Apr 22	May 6	Oct 16	Oct 30	176

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 24 locations is 2,224; LaMoure's own reading is shown below.

Annual growing degree days for LaMoure (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	2,365	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	4,173	cool-season crops (brassicas, greens)

Hardiness zone 4b in North Dakota

Zone 4b means an average annual extreme minimum winter temperature of about −25 to −20 °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. North Dakota spans 3 hardiness zones in this dataset — see all North Dakota locations for the full range, including zones3b, 4a.

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

Frequently asked questions

What does USDA hardiness zone 4b mean in North Dakota?: Zone 4b means an average annual extreme minimum winter temperature of −25 to −20 °F — the standard USDA measure of which perennials survive winter. 24 locations in North Dakota fall in this zone. It does not set planting dates; see the frost calendar below for that.
Where in North Dakota's zone 4b is the growing season longest?: Lidgerwood runs the longest season on this page at about 157 days; Hettinger is shortest at about 103 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 North Dakota's zone 4b?: Using LaMoure'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 North Dakota's zone 4b 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 24 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.