USDA Zone 4a Planting Calendar (2026)
Zone 4a (-30 to -25°F) has an average last spring frost on May 10 and first fall frost on Sep 25 — about 138 growing days. Typical areas: northern Wisconsin, Fargo ND.
How to use the zone 4a planting calendar
Every planting date on this page is calculated from zone 4a's average frost dates. Because your last spring frost lands around May 10 and your first fall frost around Sep 25, you have roughly 138 frost-free days to work with — a short growing season. The table below lists, for each of 20 common vegetables, when to start seeds indoors, when to sow or transplant outdoors, and when you can expect your first harvest.
Frost dates are averages, not guarantees. In a cold year the last frost can arrive 1-2 weeks later, so keep row covers handy for tender seedlings in May. Click any vegetable name to open a detailed zone 4a guide with spacing, companions, container tips and troubleshooting.
Cool-season crops for zone 4a
These tolerate light frost and go out first, 2-4 weeks before your May 10 last frost, and again in late summer for a fall crop: lettuce, carrot, broccoli, spinach, kale, onion, garlic, potato, peas, radish, beet, cabbage, cauliflower.
Warm-season crops for zone 4a
These need warm soil and frost-free weather, so plant them after May 10: tomato, pepper, cucumber, corn, bush beans, summer squash, zucchini. In a short season, start the slowest ones indoors to be sure they ripen before Sep.
| Vegetable | Start Indoors | Sow / Transplant | Harvest From |
|---|---|---|---|
| Beet | — | Apr 12 | Jun 6 |
| 🥦 Broccoli | Apr 5 | Apr 26 | Jun 30 |
| 🫘 Bush Beans | — | May 17 | Jul 11 |
| 🥬 Cabbage | Mar 29 | Apr 26 | Jul 15 |
| 🥕 Carrot | — | Apr 19 | Jun 28 |
| 🥦 Cauliflower | Mar 29 | Apr 26 | Jul 10 |
| 🌽 Corn | — | May 24 | Aug 12 |
| 🥒 Cucumber | Apr 19 | May 24 | Jul 18 |
| 🧄 Garlic | — | Oct 25 | Jun 22 |
| 🥬 Kale | Apr 5 | Apr 19 | Jun 13 |
| 🥬 Lettuce | Apr 12 | Apr 19 | Jun 3 |
| 🧅 Onion | Mar 1 | Apr 12 | Jul 21 |
| 🟢 Peas | — | Mar 29 | May 28 |
| 🫑 Pepper | Mar 15 | May 24 | Aug 2 |
| 🥔 Potato | — | Apr 26 | Jul 25 |
| 🌶️ Radish | — | Apr 12 | May 10 |
| 🍃 Spinach | — | Apr 5 | May 15 |
| 🎃 Summer Squash | Apr 19 | May 17 | Jul 6 |
| 🍅 Tomato | Mar 29 | May 17 | Jul 31 |
| 🥒 Zucchini | Apr 19 | May 17 | Jul 6 |
Spring, summer and fall planting in zone 4a
Spring (May): As soon as the soil can be worked, direct sow hardy cool-season crops and set out frost-tolerant transplants. This is your window for peas, lettuce, spinach and the brassicas before summer heat arrives.
Early summer (after May 10): Once frost danger passes and soil warms past 60°F, transplant tomatoes, peppers and squash and direct sow beans and cucumbers. This is the heart of the zone 4a growing season.
Late summer to fall (before Sep 25):Sow a second round of quick cool-season crops for a fall harvest. Count back each crop's days-to-harvest from Sep 25 to find the latest safe sowing date, and use row covers to stretch the season a few extra weeks.
Zone 4a planting FAQ
What planting zone is northern Wisconsin?
Areas like northern Wisconsin, Fargo ND fall in USDA hardiness zone 4a, defined by an average annual minimum temperature of -30 to -25°F. Your average last spring frost is around May 10 and your first fall frost around Sep 25.
When is the last frost in zone 4a?
The average last spring frost in zone 4a is around May 10. Wait until after this date before transplanting warm-season crops like tomatoes, peppers and squash. Cool-season crops can go out 2-4 weeks earlier because they tolerate light frost.
How long is the growing season in zone 4a?
Zone 4a has roughly 138 frost-free days between the last spring frost (May 10) and first fall frost (Sep 25). That is a short season — focus on fast-maturing and cool-season crops, and start heat lovers indoors.
What vegetables grow best in zone 4a?
Reliable choices for zone 4a include cool-season crops such as lettuce, carrot, broccoli, spinach planted in early spring, and warm-season crops such as tomato, pepper, cucumber, corn planted after the last frost. See the full table below for exact dates.
Can I grow a fall garden in zone 4a?
Yes. With a first frost around Sep 25, you can plant a second round of quick cool-season crops in mid to late summer. Count back the days-to-harvest from Sep 25 to find your fall planting date.
When should I start seeds indoors in zone 4a?
Most warm-season seedlings are started indoors 6-8 weeks before the last frost — that means roughly May for zone 4a. Tomatoes, peppers and eggplant benefit most from an indoor head start in this zone.