Zone 3b Frost Dates & Planting Calendar
USDA Zone 3b has average coldest-winter lows of −35°F to −30°F. Across the 4 cities we track in this zone, the typical last spring frost is around May 17 and the typical first fall frost around September 23.
Winter low −35°F to −30°F
Typical last frost May 17
Typical first frost September 23
Cities 4
Hardiness zones describe winter cold, not frost timing (why that matters). For dates specific to your town, look up your ZIP code.
Zone 3b Planting Calendar
| Crop | Start indoors | Direct sow | Transplant | Fall planting | Maturity | Notes |
|---|---|---|---|---|---|---|
| Tomato | Mar 22 – Apr 5 | — | May 24 – May 31 | — | 60–85 days | Start indoors 6-8 weeks before last frost; transplant out 1-2 weeks after last frost once soil has warmed. |
| Pepper | Mar 8 – Mar 22 | — | May 24 – Jun 7 | — | 60–90 days | Slow to germinate; start indoors 8-10 weeks before last frost. Transplant only once nights stay above 55F, 1-3 weeks after last frost. |
| Eggplant | Mar 8 – Mar 22 | — | May 31 – Jun 7 | — | 65–85 days | Warm-season crop, similar timing to pepper; needs consistently warm soil (65F+) to transplant. |
| Cucumber | Apr 19 – Apr 26 | May 24 – May 31 | May 24 – May 31 | — | 50–65 days | Can be started indoors 3-4 weeks before transplanting, or direct-sown 1-2 weeks after last frost once soil is warm. |
| Zucchini | Apr 26 – May 3 | May 24 – Jun 7 | May 24 – May 31 | — | 45–55 days | Fast-growing squash; direct sow 1-3 weeks after last frost, or start indoors 2-3 weeks early for a head start. |
| Winter Squash | Apr 19 – Apr 26 | May 24 – Jun 7 | May 24 – May 31 | — | 80–110 days | Long season; direct sow after soil warms, or start indoors 3-4 weeks before last frost in short-season climates. |
| Pumpkin | — | May 24 – Jun 7 | — | — | 90–120 days | Direct sow 1-3 weeks after last frost; back-time from your first fall frost so the 90-120 day maturity window lands before it. |
| Watermelon | Apr 19 – Apr 26 | — | May 31 – Jun 7 | — | 70–90 days | Needs warm soil (65F+); start indoors 3-4 weeks before last frost, transplant 2-3 weeks after last frost. |
| Cantaloupe | Apr 19 – Apr 26 | — | May 31 – Jun 7 | — | 70–90 days | Same warm-soil requirements as watermelon; avoid disturbing roots when transplanting. |
| Corn | — | May 17 – May 31 | — | — | 60–100 days | Direct sow at last frost to 2 weeks after, once soil reaches 60F; does not transplant well. Succession sow every 2 weeks. |
| Green Bean | — | May 17 – May 31 | — | — | 50–65 days | Direct sow at last frost to 2 weeks after, once soil has warmed; frost-tender, do not rush. |
| Pea | — | Apr 5 – Apr 19 | — | — | 55–70 days | Cold-hardy; direct sow 4-6 weeks before last frost as soon as soil can be worked. |
| Lettuce | — | Apr 19 – May 3 | — | Jul 29 – Aug 12 | 45–60 days | Cold-hardy; direct sow 2-4 weeks before last frost. Also transplantable from indoor starts. |
| Spinach | — | Apr 5 – Apr 19 | — | Jul 29 – Aug 12 | 40–50 days | Very cold-hardy; direct sow 4-6 weeks before last frost as soon as soil can be worked. |
| Kale | — | Apr 19 – May 3 | — | Jul 15 – Jul 29 | 50–65 days | Cold-hardy; direct sow 2-4 weeks before last frost or start indoors for earlier transplants. |
| Arugula | — | Apr 19 – May 3 | — | Aug 12 – Aug 19 | 30–40 days | Fast-growing, cold-tolerant green; direct sow 2-4 weeks before last frost, succession sow every 2-3 weeks. |
| Swiss Chard | — | Apr 26 – May 10 | — | — | 50–60 days | Fairly cold-hardy; direct sow 1-3 weeks before last frost. Tolerates light frost in fall too. |
| Broccoli | Mar 29 – Apr 12 | — | Apr 26 – May 3 | Jul 22 – Jul 29 | 55–80 days | Start indoors 5-7 weeks before last frost; transplant out 2-3 weeks before last frost (hardens off to light frost). |
| Cauliflower | Mar 29 – Apr 12 | — | May 3 – May 10 | Jul 15 – Jul 22 | 55–85 days | Fussier than broccoli about temperature swings; start indoors 5-7 weeks before last frost, transplant 1-2 weeks before last frost. |
| Cabbage | Mar 29 – Apr 12 | — | Apr 19 – May 3 | Jul 15 – Jul 29 | 60–100 days | Cold-hardy; start indoors 5-7 weeks before last frost, transplant 2-4 weeks before last frost. |
| Brussels Sprouts | Mar 29 – Apr 12 | — | Apr 26 – May 10 | — | 90–110 days | Long-season crop best timed to mature after a light fall frost for sweetest flavor; start indoors 5-7 weeks before last frost. |
| Carrot | — | Apr 19 – May 3 | — | Jul 1 – Jul 15 | 60–80 days | Direct sow only (does not transplant); sow 2-4 weeks before last frost, as soon as soil can be worked. |
| Beet | — | Apr 19 – May 3 | — | Jul 15 – Jul 29 | 50–65 days | Direct sow 2-4 weeks before last frost; tolerates light frost. |
| Radish | — | Apr 12 – Apr 26 | — | Aug 12 – Aug 26 | 22–30 days | Very fast and cold-hardy; direct sow 3-5 weeks before last frost, as soon as soil can be worked. |
| Turnip | — | Apr 19 – May 3 | — | Jul 15 – Jul 29 | 40–60 days | Cold-hardy; direct sow 2-4 weeks before last frost. |
| Onion | Mar 8 – Mar 22 | — | Apr 19 – May 3 | — | 90–120 days | Start seeds indoors 8-10 weeks before last frost (or use sets/transplants); set out 2-4 weeks before last frost, very cold-tolerant as seedlings. |
| Garlic | — | — | — | Aug 26 – Sep 9 | 240–270 days | Fall-planted crop only; not planted in spring in most climates. |
| Potato | — | Apr 19 – May 3 | — | — | 70–120 days | Plant seed potatoes 2-4 weeks before last frost, as soon as soil can be worked and is above 45F; light frost on emerging foliage is usually tolerated. |
| Sweet Potato | — | — | May 31 – Jun 14 | — | 90–120 days | Set out slips 2-4 weeks after last frost once soil is thoroughly warm (65F+); very frost/cold sensitive. |
| Asparagus | — | — | Apr 19 – May 3 | — | 730–1095 days | Perennial; plant crowns 2-4 weeks before last frost as soon as soil can be worked. Takes 2-3 years to full production. |
| Crop | Start indoors | Direct sow | Transplant | Fall planting | Maturity | Notes |
|---|---|---|---|---|---|---|
| Basil | Apr 5 – Apr 12 | — | May 24 – May 31 | — | 50–70 days | Very frost/cold sensitive; start indoors 5-6 weeks before last frost, transplant only after all danger of frost (1-2 weeks after) and nights stay warm. |
| Cilantro | — | Apr 26 – May 10 | — | Jul 29 – Aug 12 | 45–70 days | Cool-season, bolts in heat; direct sow 1-3 weeks before last frost, succession sow through spring. |
| Parsley | Mar 22 – Apr 5 | — | May 3 – May 10 | — | 70–90 days | Slow to germinate; start indoors 6-8 weeks before last frost, transplant 1-2 weeks before last frost (biennial, cold-tolerant). |
| Dill | — | Apr 26 – May 10 | — | — | 40–60 days | Taprooted, does not transplant well; direct sow 1-3 weeks before last frost, succession sow through summer. |
| Oregano | Mar 22 – Apr 5 | — | May 17 – May 24 | — | 80–90 days | Perennial herb; start indoors 6-8 weeks before last frost, transplant around/just after last frost date. |
| Thyme | Mar 22 – Apr 5 | — | May 17 – May 24 | — | 85–95 days | Perennial herb, slow from seed; start indoors 6-8 weeks before last frost, transplant around/after last frost. |
| Crop | Start indoors | Direct sow | Transplant | Fall planting | Maturity | Notes |
|---|---|---|---|---|---|---|
| Sunflower | — | May 24 – Jun 7 | — | — | 70–100 days | Direct sow 1-3 weeks after last frost once soil has warmed; taprooted, resents transplanting. |
| Zinnia | Apr 19 – Apr 26 | May 24 – Jun 7 | May 24 – May 31 | — | 60–70 days | Frost-tender; direct sow 1-3 weeks after last frost, or start indoors 3-4 weeks early for earlier blooms. |
| Marigold | Apr 5 – Apr 19 | — | May 24 – May 31 | — | 45–60 days | Frost-tender; start indoors 4-6 weeks before last frost, transplant after all frost danger has passed. |
| Cosmos | Apr 19 – Apr 26 | May 24 – Jun 7 | May 24 – May 31 | — | 60–90 days | Easy from direct seed 1-3 weeks after last frost; can also start indoors 3-4 weeks early. |
| Nasturtium | — | May 24 – Jun 7 | — | — | 50–65 days | Frost-tender, resents root disturbance; direct sow 1-3 weeks after last frost once soil has warmed. |
| Dahlia | — | — | May 24 – Jun 7 | — | 90–120 days | Plant tubers 1-3 weeks after last frost once soil is warm (60F+); very frost-sensitive. |
Date ranges are estimates based on university extension guidelines and this city's NOAA frost normals — not a guarantee. Scroll to see all columns on narrow screens.
Cities in Zone 3b
| City | Last frost | First frost |
|---|---|---|
| Hibbing, MN | Jun 5 | Sep 8 |
| Bemidji, MN | May 17 | Sep 26 |
| Havre, MT | May 15 | Sep 23 |
| Rugby, ND | May 17 | Sep 23 |
States with Zone 3b cities
- Minnesota (2)
- Montana (1)
- North Dakota (1)
Frequently Asked Questions
What is the temperature range for Zone 3b?
Zone 3b is defined by an average annual extreme minimum winter temperature of −35°F to −30°F (USDA 2023 Plant Hardiness Zone Map).
When is the last frost in Zone 3b?
Typically around May 17, though it varies by location. Hardiness zones measure winter cold, not frost timing, so two places in the same zone can have last frosts weeks apart — check your city's page for local dates.
When is the first frost in Zone 3b?
Typically around September 23 across the cities we track in Zone 3b.