What does USDA hardiness zone 3b mean in North Dakota?

Zone 3b means an average annual extreme minimum winter temperature of −35 to −30 °F — the standard USDA measure of which perennials survive winter. 21 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 3b is the growing season longest?

Tioga runs the longest season on this page at about 136 days; Willow is shortest at about 119 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 3b?

Using Adams's frost dates (this page's median-season location): start seeds indoors about Mar 20 – Apr 3, then transplant outside about May 22 – May 29. 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 3b 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 21 locations listed (see the table above for each location's own dates).

USDA zone 3b in North Dakota

−35 to −30 °F avg. annual extreme minimum · 21 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 3b covers 21 locations across North Dakota (average annual extreme minimum −35 to −30 °F): Adams, ND, Alamo, ND, Balta, ND, Bantry, ND, Belcourt, ND, Cando, ND, and 15 more. Average last spring frost across this group ranges May 11 (Tioga) to May 22 (Rolette), and growing seasons run 119–136 days (Willow to Tioga) — 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 Adams, this group's median-season location.

USDA zone: 3b−35 to −30 °F
Last frost range: May 11–May 22avg, 32°F
First frost range: Sep 17–Sep 27avg, 32°F
Growing season range: 119–136days

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)
Adams *	Edmore	Edmore 4nw	May 15	Sep 22	128
Alamo	Wildrose, McGregor	Wildrose 3nw	May 18	Sep 20	124
Balta	Wolford	Rugby	May 17	Sep 23	129
Bantry	Upham, Kramer, Newburg, Deering	Upham 3 N	May 15	Sep 25	132
Belcourt	St. John	Belcourt Keya Radio	May 19	Sep 24	126
Cando	—	Leeds	May 15	Sep 27	133
East Dunseith	Bottineau	Bottineau	May 15	Sep 25	133
Egeland	Sarles, Rocklake, Hansboro	Hansboro 4 Nne	May 18	Sep 23	127
Flaxton	—	Kenmare 1 Wsw	May 15	Sep 23	129
Fortuna	—	Fortuna 1 W	May 19	Sep 17	121
Grenora	Homestead, Medicine Lake	Medicine Lake 3 Se	May 16	Sep 18	125
Grenora	Westby	Westby	May 18	Sep 21	125
Loma	Langdon, Munich, Milton, Nekoma, Fairdale, Osnabrock, +3 more	Langdon Exp Farm	May 17	Sep 26	132
Portal	Noonan, Columbus	Crosby	May 17	Sep 23	128
Rolette	Mylo, Bisbee	Rolette 3se	May 22	Sep 20	120
Rolla	Perth	Rolla 1ne	May 20	Sep 26	128
Sherwood	—	Mohall	May 17	Sep 23	127
Tioga	—	Tioga 1e	May 11	Sep 26	136
Towner	—	Towner 2 Ne	May 17	Sep 22	126
Westhope	Antler, Maxbass, Souris	Westhope	May 14	Sep 25	133
Willow	—	Willow City	May 21	Sep 20	119

* Adams 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 (Adams, representative)

Computed from Adams's average frost dates — the median-season location in this North Dakotazone 3b 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 Adams (North Dakota, zone 3b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 20 – Apr 3	May 22 – May 29	Jul 21 – Aug 10	—	matures comfortably
Pepper	Very tender	Mar 6 – Mar 20	May 29 – Jun 5	Jul 28 – Aug 27	—	matures comfortably
Cucumber	Tender	Apr 17 – Apr 24	May 22 – May 29	Jul 11 – Jul 31	—	matures comfortably
Summer squash / zucchini	Tender	—	May 22 – May 29	Jul 6 – Jul 21	—	matures comfortably
Bush bean	Tender	—	May 22 – May 29	Jul 11 – Jul 21	Jul 24 – Aug 3	matures comfortably
Sweet corn	Tender	—	May 15 – May 29	Jul 14 – Aug 13	—	matures comfortably
Basil	Very tender	Apr 3 – Apr 17	May 22 – May 29	Jun 21 – Jul 6	—	matures comfortably
Lettuce	Half-hardy	Apr 3 – Apr 17	Apr 17 – May 1	Jun 1 – Jun 16	Jul 10 – Jul 25	matures comfortably
Pea	Hardy	—	Apr 3 – Apr 17	May 28 – Jun 12	Jun 30 – Jul 15	matures comfortably
Spinach	Hardy	—	Apr 3 – Apr 17	May 13 – May 23	Jul 20 – Jul 30	matures comfortably
Carrot	Half-hardy	—	Apr 24 – May 1	Jun 23 – Jul 13	Jun 20 – Jul 10	matures comfortably
Broccoli	Half-hardy	Mar 20 – Apr 3	Apr 17 – May 1	Jun 11 – Jul 1	Jun 25 – Jul 15	matures comfortably

Which crops fit this growing season

Using Adams's own 128-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 (Adams)

From NOAA's 1991–2020 Climate Normals at station USC00322525. 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), Adams.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	May 26	Jun 10	Sep 15	Sep 25	108
32°F (freeze)	May 15	May 31	Sep 22	Oct 3	128
28°F	May 4	May 17	Oct 1	Oct 14	147
24°F	Apr 27	May 8	Oct 10	Oct 25	166

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 21 locations is 1,890; Adams's own reading is shown below.

Annual growing degree days for Adams (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	1,787	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	3,419	cool-season crops (brassicas, greens)

Hardiness zone 3b in North Dakota

Zone 3b means an average annual extreme minimum winter temperature of about −35 to −30 °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 zones4a, 4b.

Explore zone 3b in other states at zone 3b, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 3b mean in North Dakota?: Zone 3b means an average annual extreme minimum winter temperature of −35 to −30 °F — the standard USDA measure of which perennials survive winter. 21 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 3b is the growing season longest?: Tioga runs the longest season on this page at about 136 days; Willow is shortest at about 119 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 3b?: Using Adams's frost dates (this page's median-season location): start seeds indoors about Mar 20 – Apr 3, then transplant outside about May 22 – May 29. 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 3b 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 21 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.