Duluth, Minnesota: planting zone & frost dates
Duluth is in USDA plant hardiness zone 4b, where the average coldest winter night reaches -25 to -20°F (-31.7 to -28.9°C). The typical last spring frost is around May 22 and the first fall frost around Oct 5.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | Jun 1 | Sep 25 |
| Typical planning date (30% risk) | May 22 | Oct 5 |
| Median (50%) | May 14 | Oct 12 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station DULUTH HARBOR STN, MN (USC00212246), 2.1 mi (3.4 km) from the city center and 364 ft lower than the city center (-111 m). Record used for the 1991–2020 normals: 14 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Duluth
Duluth spans more than one half-zone. Share of the city's land area by zone (via its 10 ZIP codes): 4b (83%), 4a (13%), 5a (4%). The headline zone is the one covering the most land. Look up your ZIP for your exact zone.
Vegetable planting calendar for Duluth
Dates are counted from the 30%-risk frost dates above (last frost May 22, first frost Oct 5). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 27 – Apr 10 | May 29 – Jun 12 | — | — |
| Pepper | Mar 13 – Mar 27 | Jun 5 – Jun 19 | — | — |
| Lettuce | Apr 10 – Apr 24 | May 8 – May 29 | Apr 24 – Jun 5 | Jul 27 – Aug 24 |
| Green Beans | — | — | May 29 – Jul 3 | Jul 13 – Jul 27 |
| Sweet Corn | — | — | May 29 – Jun 26 | — |
| Zucchini & Summer Squash | Apr 24 – May 1 | May 29 – Jun 12 | May 29 – Jun 19 | Jul 13 – Jul 27 |
| Cucumber | Apr 24 – May 1 | Jun 5 – Jun 12 | May 29 – Jun 19 | Jul 13 – Jul 27 |
| Carrot | — | — | May 1 – Jun 5 | Jul 13 – Jul 27 |
| Onion | Feb 27 – Mar 13 | Apr 24 – May 8 | — | — |
| Potato | — | Apr 24 – May 15 | — | — |
| Basil | Apr 10 – Apr 24 | Jun 5 – Jun 19 | Jun 5 – Jun 26 | — |
| Spinach | — | — | Apr 10 – May 8 | Aug 10 – Sep 7 |
| Kale | Mar 27 – Apr 10 | Apr 24 – May 15 | Apr 24 – May 15 | Jul 27 – Aug 24 |
| Broccoli | Mar 27 – Apr 10 | May 8 – May 29 | — | Jul 13 – Jul 27 |
| Peas | — | — | Apr 10 – May 1 | Jul 27 – Aug 10 |
| Eggplant | Mar 13 – Mar 27 | Jun 5 – Jun 19 | — | — |
| Cabbage | Mar 27 – Apr 10 | Apr 24 – May 8 | — | Jul 13 – Jul 27 |
| Radish | — | — | Apr 17 – Jun 5 | Aug 24 – Sep 21 |
| Strawberry | — | Apr 24 – May 15 | — | — |
| Beets | — | — | May 1 – Jun 12 | Jul 27 – Aug 10 |
Nearby cities in Minnesota
- Woodbury — zone 5a, last frost May 1, first frost Oct 5
- Brooklyn Park — zone 5a, last frost May 6, first frost Oct 2
- St. Paul — zone 5a, last frost May 1, first frost Oct 7
- Minneapolis — zone 5a, last frost Apr 30, first frost Oct 10
- Plymouth — zone 5a, last frost May 4, first frost Oct 5
- Bloomington — zone 5a, last frost Apr 30, first frost Oct 11
More: all Minnesota cities · other zone 4b cities: Rochester, MN, Lakeville, MN
Duluth gardening questions
When is the last frost in Duluth, MN?
Plan around May 22. At NOAA's Duluth Harbor Stn, MN station, 2.1 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by May 14, and after Jun 1 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 29. The 90% and 10% dates are 38 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Duluth, MN?
Start seeds indoors Mar 27 – Apr 10 and set transplants outside May 29 – Jun 12, once nights stay above 50°F and the soil is near 60°F. That leaves 136 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Duluth?
About 149 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 124 days, and in 1 year in 10 it runs 175 days or more. In fall there is a 10% chance of frost by Sep 25 and a 30% chance by Oct 5. That is the shortest of the 9 Minnesota cities on this site.
When should I plant a fall garden in Duluth?
Count back from the first fall frost (Oct 5): transplant broccoli Jul 13 – Jul 27; sow kale Jul 27 – Aug 24; sow lettuce Jul 27 – Aug 24; sow radishes Aug 24 – Sep 21. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 25. How the math works: succession and fall planting.
Did Duluth's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Duluth is zone 4b on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.
Is all of Duluth in zone 4b?
No. Zone 4b covers about 83% of the city's land; the rest is in 4a (13%), 5a (4%), measured across the city's 10 ZIP codes. Check your own ZIP code in the table above or with the ZIP lookup.