USDA Zone 3a Planting Calendar (2026)
Zone 3a (-40 to -35°F) has an average last spring frost on May 15 and first fall frost on Sep 15 — about 123 growing days. Typical areas: northern Minnesota, International Falls.
How to use the zone 3a planting calendar
Every planting date on this page is calculated from zone 3a's average frost dates. Because your last spring frost lands around May 15 and your first fall frost around Sep 15, you have roughly 123 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 3a guide with spacing, companions, container tips and troubleshooting.
Cool-season crops for zone 3a
These tolerate light frost and go out first, 2-4 weeks before your May 15 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 3a
These need warm soil and frost-free weather, so plant them after May 15: 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 17 | Jun 11 |
| 🥦 Broccoli | Apr 10 | May 1 | Jul 5 |
| 🫘 Bush Beans | — | May 22 | Jul 16 |
| 🥬 Cabbage | Apr 3 | May 1 | Jul 20 |
| 🥕 Carrot | — | Apr 24 | Jul 3 |
| 🥦 Cauliflower | Apr 3 | May 1 | Jul 15 |
| 🌽 Corn | — | May 29 | Aug 17 |
| 🥒 Cucumber | Apr 24 | May 29 | Jul 23 |
| 🧄 Garlic | — | Oct 30 | Jun 27 |
| 🥬 Kale | Apr 10 | Apr 24 | Jun 18 |
| 🥬 Lettuce | Apr 17 | Apr 24 | Jun 8 |
| 🧅 Onion | Mar 6 | Apr 17 | Jul 26 |
| 🟢 Peas | — | Apr 3 | Jun 2 |
| 🫑 Pepper | Mar 20 | May 29 | Aug 7 |
| 🥔 Potato | — | May 1 | Jul 30 |
| 🌶️ Radish | — | Apr 17 | May 15 |
| 🍃 Spinach | — | Apr 10 | May 20 |
| 🎃 Summer Squash | Apr 24 | May 22 | Jul 11 |
| 🍅 Tomato | Apr 3 | May 22 | Aug 5 |
| 🥒 Zucchini | Apr 24 | May 22 | Jul 11 |
Spring, summer and fall planting in zone 3a
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 15): 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 3a growing season.
Late summer to fall (before Sep 15):Sow a second round of quick cool-season crops for a fall harvest. Count back each crop's days-to-harvest from Sep 15 to find the latest safe sowing date, and use row covers to stretch the season a few extra weeks.
Zone 3a planting FAQ
What planting zone is northern Minnesota?
Areas like northern Minnesota, International Falls fall in USDA hardiness zone 3a, defined by an average annual minimum temperature of -40 to -35°F. Your average last spring frost is around May 15 and your first fall frost around Sep 15.
When is the last frost in zone 3a?
The average last spring frost in zone 3a is around May 15. 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 3a?
Zone 3a has roughly 123 frost-free days between the last spring frost (May 15) and first fall frost (Sep 15). That is a short season — focus on fast-maturing and cool-season crops, and start heat lovers indoors.
What vegetables grow best in zone 3a?
Reliable choices for zone 3a 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 3a?
Yes. With a first frost around Sep 15, you can plant a second round of quick cool-season crops in mid to late summer. Count back the days-to-harvest from Sep 15 to find your fall planting date.
When should I start seeds indoors in zone 3a?
Most warm-season seedlings are started indoors 6-8 weeks before the last frost — that means roughly May for zone 3a. Tomatoes, peppers and eggplant benefit most from an indoor head start in this zone.