Duluth, MN planting zone & frost dates
Duluth is in USDA hardiness zone 4b. The last spring frost usually comes around May 14 and the first fall frost around October 12, for a growing season of about 149 days.
Planting calendar for Duluth
Dates are counted from the average last spring frost (May 14) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Mar 19 – Apr 2 Transplant outdoors: May 21 – May 28 |
| Peppers | Start seeds indoors: Mar 5 – Mar 19 Transplant outdoors: May 28 – Jun 4 |
| Eggplant | Start seeds indoors: Mar 5 – Mar 19 Transplant outdoors: May 28 – Jun 4 |
| Broccoli | Start seeds indoors: Mar 5 – Mar 19 Transplant outdoors: Apr 16 – Apr 30 |
| Cabbage | Start seeds indoors: Mar 5 – Mar 19 Transplant outdoors: Apr 16 – Apr 30 |
| Onions (sets) | Plant outdoors: Apr 16 – Apr 30 |
| Peas | Sow outdoors: Apr 2 – Apr 16 |
| Spinach | Sow outdoors: Apr 2 – Apr 16 |
| Lettuce | Sow outdoors: Apr 16 – Apr 30 |
| Carrots | Sow outdoors: Apr 16 – Apr 30 |
| Potatoes | Plant outdoors: Apr 16 – Apr 30 |
| Beans | Sow outdoors: May 21 – May 28 |
| Sweet corn | Sow outdoors: May 21 – May 28 |
| Cucumbers | Sow outdoors: May 21 – May 28 |
| Squash & zucchini | Sow outdoors: May 21 – May 28 |
| Basil | Start seeds indoors: Apr 2 – Apr 16 Transplant outdoors: May 21 – May 28 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 17 (8 weeks before the average first fall frost on Oct 12).
Useful for zone 4b gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 24 | May 14 | Jun 1 |
| First 32°F frost in fall is before | Oct 26 | Oct 12 | Sep 25 |
How to read it: in spring there is a 10% chance of a frost after June 1, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 25. A hard freeze (28°F) usually ends around April 29.
Hardiness zone by ZIP code in Duluth
- 55802 zone 5a
- 55803 zone 4a
- 55804 zone 4b
- 55805 zone 4b
- 55806 zone 4b
- 55807 zone 4b
- 55808 zone 4b
- 55810 zone 4b
- 55811 zone 4b
- 55812 zone 4b
- 55814 zone 4b
- 55815 zone 4b
- 55816 zone 5a
Nearby cities
- Cloquet zone 4a, last frost May 26
- Hibbing zone 3b, last frost Jun 5
- Grand Rapids zone 4a, last frost May 17
- North Branch zone 4b, last frost May 19
- Forest Lake zone 4b, last frost May 3
- East Bethel zone 4b, last frost May 1
- Hugo zone 4b, last frost Apr 23
- Stillwater zone 4b, last frost Apr 22
Questions
What growing zone is Duluth, MN?
Duluth is in USDA Plant Hardiness Zone 4b (average extreme winter low -25°F to -20°F), according to the USDA 2023 map. Some ZIP codes of the city fall in zones 4a, 5a.
When is the last frost in Duluth?
The average last spring frost (32°F) in Duluth is May 14. There is still a 10% chance of frost until June 1.
When can I plant tomatoes in Duluth?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 21 – May 28. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Duluth Harbor Stn, MN (USC00212246), 2.1 km (1.3 mi) from the city center, elevation 186 m, based on 14 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.