Bismarck, ND planting zone & frost dates
Bismarck is in USDA hardiness zone 4a. The last spring frost usually comes around May 10 and the first fall frost around September 30, for a growing season of about 142 days.
Planting calendar for Bismarck
Dates are counted from the average last spring frost (May 10) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Mar 15 – Mar 29 Transplant outdoors: May 17 – May 24 |
| Peppers | Start seeds indoors: Mar 1 – Mar 15 Transplant outdoors: May 24 – May 31 |
| Eggplant | Start seeds indoors: Mar 1 – Mar 15 Transplant outdoors: May 24 – May 31 |
| Broccoli | Start seeds indoors: Mar 1 – Mar 15 Transplant outdoors: Apr 12 – Apr 26 |
| Cabbage | Start seeds indoors: Mar 1 – Mar 15 Transplant outdoors: Apr 12 – Apr 26 |
| Onions (sets) | Plant outdoors: Apr 12 – Apr 26 |
| Peas | Sow outdoors: Mar 29 – Apr 12 |
| Spinach | Sow outdoors: Mar 29 – Apr 12 |
| Lettuce | Sow outdoors: Apr 12 – Apr 26 |
| Carrots | Sow outdoors: Apr 12 – Apr 26 |
| Potatoes | Plant outdoors: Apr 12 – Apr 26 |
| Beans | Sow outdoors: May 17 – May 24 |
| Sweet corn | Sow outdoors: May 17 – May 24 |
| Cucumbers | Sow outdoors: May 17 – May 24 |
| Squash & zucchini | Sow outdoors: May 17 – May 24 |
| Basil | Start seeds indoors: Mar 29 – Apr 12 Transplant outdoors: May 17 – May 24 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 5 (8 weeks before the average first fall frost on Sep 30).
Useful for zone 4a gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 30 | May 10 | May 23 |
| First 32°F frost in fall is before | Oct 13 | Sep 30 | Sep 16 |
How to read it: in spring there is a 10% chance of a frost after May 23, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 16. A hard freeze (28°F) usually ends around May 1.
Hardiness zone by ZIP code in Bismarck
- 58501 zone 4a
- 58502 zone 4a
- 58503 zone 4a
- 58504 zone 4a
- 58505 zone 4a
- 58506 zone 4a
- 58507 zone 4a
Nearby cities
- Mandan zone 4a, last frost May 13
- Minot zone 4a, last frost May 10
- Dickinson zone 4a, last frost May 20
- Jamestown zone 4b, last frost May 8
- Williston zone 4a, last frost May 21
- West Fargo zone 4a, last frost May 10
- Grand Forks zone 4a, last frost May 10
- Fargo zone 4a, last frost May 5
Questions
What growing zone is Bismarck, ND?
Bismarck is in USDA Plant Hardiness Zone 4a (average extreme winter low -30°F to -25°F), according to the USDA 2023 map.
When is the last frost in Bismarck?
The average last spring frost (32°F) in Bismarck is May 10. There is still a 10% chance of frost until May 23.
When can I plant tomatoes in Bismarck?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 17 – May 24. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Bismarck 2.4 Nnw, ND (USC00320817), 3.0 km (1.9 mi) from the city center, elevation 558 m, based on 12 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.