Zone 4a Frost Dates & Planting Calendar
USDA Zone 4a has average coldest-winter lows of −30°F to −25°F. Across the 26 cities we track in this zone, the typical last spring frost is around May 10 and the typical first fall frost around September 29.
Winter low −30°F to −25°F
Typical last frost May 10
Typical first frost September 29
Cities 26
Hardiness zones describe winter cold, not frost timing (why that matters). For dates specific to your town, look up your ZIP code.
Zone 4a Planting Calendar
| Crop | Start indoors | Direct sow | Transplant | Fall planting | Maturity | Notes |
|---|---|---|---|---|---|---|
| Tomato | Mar 15 – Mar 29 | — | May 17 – May 24 | — | 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 1 – Mar 15 | — | May 17 – May 31 | — | 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 1 – Mar 15 | — | May 24 – May 31 | — | 65–85 days | Warm-season crop, similar timing to pepper; needs consistently warm soil (65F+) to transplant. |
| Cucumber | Apr 12 – Apr 19 | May 17 – May 24 | May 17 – May 24 | — | 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 19 – Apr 26 | May 17 – May 31 | May 17 – May 24 | — | 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 12 – Apr 19 | May 17 – May 31 | May 17 – May 24 | — | 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 17 – May 31 | — | — | 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 12 – Apr 19 | — | May 24 – May 31 | — | 70–90 days | Needs warm soil (65F+); start indoors 3-4 weeks before last frost, transplant 2-3 weeks after last frost. |
| Cantaloupe | Apr 12 – Apr 19 | — | May 24 – May 31 | — | 70–90 days | Same warm-soil requirements as watermelon; avoid disturbing roots when transplanting. |
| Corn | — | May 10 – May 24 | — | — | 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 10 – May 24 | — | — | 50–65 days | Direct sow at last frost to 2 weeks after, once soil has warmed; frost-tender, do not rush. |
| Pea | — | Mar 29 – Apr 12 | — | — | 55–70 days | Cold-hardy; direct sow 4-6 weeks before last frost as soon as soil can be worked. |
| Lettuce | — | Apr 12 – Apr 26 | — | Aug 4 – Aug 18 | 45–60 days | Cold-hardy; direct sow 2-4 weeks before last frost. Also transplantable from indoor starts. |
| Spinach | — | Mar 29 – Apr 12 | — | Aug 4 – Aug 18 | 40–50 days | Very cold-hardy; direct sow 4-6 weeks before last frost as soon as soil can be worked. |
| Kale | — | Apr 12 – Apr 26 | — | Jul 21 – Aug 4 | 50–65 days | Cold-hardy; direct sow 2-4 weeks before last frost or start indoors for earlier transplants. |
| Arugula | — | Apr 12 – Apr 26 | — | Aug 18 – Aug 25 | 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 19 – May 3 | — | — | 50–60 days | Fairly cold-hardy; direct sow 1-3 weeks before last frost. Tolerates light frost in fall too. |
| Broccoli | Mar 22 – Apr 5 | — | Apr 19 – Apr 26 | Jul 28 – Aug 4 | 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 22 – Apr 5 | — | Apr 26 – May 3 | Jul 21 – Jul 28 | 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 22 – Apr 5 | — | Apr 12 – Apr 26 | Jul 21 – Aug 4 | 60–100 days | Cold-hardy; start indoors 5-7 weeks before last frost, transplant 2-4 weeks before last frost. |
| Brussels Sprouts | Mar 22 – Apr 5 | — | Apr 19 – May 3 | — | 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 12 – Apr 26 | — | Jul 7 – Jul 21 | 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 12 – Apr 26 | — | Jul 21 – Aug 4 | 50–65 days | Direct sow 2-4 weeks before last frost; tolerates light frost. |
| Radish | — | Apr 5 – Apr 19 | — | Aug 18 – Sep 1 | 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 12 – Apr 26 | — | Jul 21 – Aug 4 | 40–60 days | Cold-hardy; direct sow 2-4 weeks before last frost. |
| Onion | Mar 1 – Mar 15 | — | Apr 12 – Apr 26 | — | 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 | — | — | — | Sep 1 – Sep 15 | 240–270 days | Fall-planted crop only; not planted in spring in most climates. |
| Potato | — | Apr 12 – Apr 26 | — | — | 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 24 – Jun 7 | — | 90–120 days | Set out slips 2-4 weeks after last frost once soil is thoroughly warm (65F+); very frost/cold sensitive. |
| Asparagus | — | — | Apr 12 – Apr 26 | — | 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 | Mar 29 – Apr 5 | — | May 17 – May 24 | — | 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 19 – May 3 | — | Aug 4 – Aug 18 | 45–70 days | Cool-season, bolts in heat; direct sow 1-3 weeks before last frost, succession sow through spring. |
| Parsley | Mar 15 – Mar 29 | — | Apr 26 – May 3 | — | 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 19 – May 3 | — | — | 40–60 days | Taprooted, does not transplant well; direct sow 1-3 weeks before last frost, succession sow through summer. |
| Oregano | Mar 15 – Mar 29 | — | May 10 – May 17 | — | 80–90 days | Perennial herb; start indoors 6-8 weeks before last frost, transplant around/just after last frost date. |
| Thyme | Mar 15 – Mar 29 | — | May 10 – May 17 | — | 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 17 – May 31 | — | — | 70–100 days | Direct sow 1-3 weeks after last frost once soil has warmed; taprooted, resents transplanting. |
| Zinnia | Apr 12 – Apr 19 | May 17 – May 31 | May 17 – May 24 | — | 60–70 days | Frost-tender; direct sow 1-3 weeks after last frost, or start indoors 3-4 weeks early for earlier blooms. |
| Marigold | Mar 29 – Apr 12 | — | May 17 – May 24 | — | 45–60 days | Frost-tender; start indoors 4-6 weeks before last frost, transplant after all frost danger has passed. |
| Cosmos | Apr 12 – Apr 19 | May 17 – May 31 | May 17 – May 24 | — | 60–90 days | Easy from direct seed 1-3 weeks after last frost; can also start indoors 3-4 weeks early. |
| Nasturtium | — | May 17 – May 31 | — | — | 50–65 days | Frost-tender, resents root disturbance; direct sow 1-3 weeks after last frost once soil has warmed. |
| Dahlia | — | — | May 17 – May 31 | — | 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 4a
| City | Last frost | First frost |
|---|---|---|
| Fargo, ND | May 5 | Oct 3 |
| Bismarck, ND | May 10 | Sep 30 |
| Grand Forks, ND | May 10 | Oct 1 |
| Minot, ND | May 10 | Oct 1 |
| Moorhead, MN | May 5 | Oct 3 |
| West Fargo, ND | May 10 | Sep 30 |
| Aberdeen, SD | May 8 | Sep 29 |
| Williston, ND | May 21 | Sep 21 |
| Mandan, ND | May 13 | Sep 27 |
| Brainerd, MN | May 8 | Sep 29 |
| Fergus Falls, MN | May 4 | Oct 5 |
| Cloquet, MN | May 26 | Sep 23 |
| Grand Rapids, MN | May 17 | Sep 24 |
| Presque Isle, ME | May 14 | Sep 26 |
| Wahpeton, ND | May 4 | Oct 3 |
| Devils Lake, ND | May 6 | Oct 5 |
| Sidney, MT | May 11 | Sep 27 |
| Watford City, ND | May 9 | Sep 27 |
| Valley City, ND | May 13 | Sep 26 |
| Bethel, AK | May 21 | Sep 22 |
| Minot Air Force Base, ND | May 11 | Sep 29 |
| Grafton, ND | May 4 | Oct 7 |
| Lincoln, ND | May 14 | Sep 30 |
| Beulah, ND | May 21 | Sep 20 |
| Stanley, ND | May 17 | Sep 23 |
| Horace, ND | May 4 | Oct 2 |
States with Zone 4a cities
- North Dakota (17)
- Minnesota (5)
- South Dakota (1)
- Maine (1)
- Montana (1)
- Alaska (1)
Frequently Asked Questions
What is the temperature range for Zone 4a?
Zone 4a is defined by an average annual extreme minimum winter temperature of −30°F to −25°F (USDA 2023 Plant Hardiness Zone Map).
When is the last frost in Zone 4a?
Typically around May 10, 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 4a?
Typically around September 29 across the cities we track in Zone 4a.