What zone 4b means for Duluth
Hardiness zones are based on the average of the coldest night of each winter over 30 years (1991 to 2020). In zone 4b, that average is -25 to -20°F (-32 to -29°C). Plants labeled hardy to zone 4b or colder should survive a typical Duluth winter. A plant rated only to a warmer zone will need a sheltered spot, a pot you can bring inside, or treating as an annual.
Not every part of Duluth is the same: its ZIP codes fall in zones 4a, 4b, 5a. Check your own ZIP code in the table below.
How Duluth compares with the rest of Minnesota
Minnesota runs from zone 3a to zone 5a on the 2023 map. About 36% of the state's ZIP codes share Duluth's zone 4b. Gardeners in colder parts of the state may need hardier plants, while those in warmer parts can grow some plants that would struggle here.
Frost dates in Duluth
These are the median dates of the last and first 32°F freeze from NOAA's 1991 to 2020 climate normals, using the weather station closest to Duluth (Duluth Harbor Stn, about 0 km away). Half of years have a later last frost, so tender plants are safest a week or two after the date. Your own garden can differ with elevation and shelter: check your exact ZIP code above.
Vegetable planting calendar for Duluth
Purdue Extension groups vegetables by how much frost they can take and times planting from the average last spring frost. Applied to Duluth's last frost of May 14:
| Group | Plant outdoors | Crops |
|---|---|---|
| Hardy crops (tolerate a hard frost) 4 to 6 weeks before the average last spring frost | April 2 to April 16 | Asparagus, broccoli, Brussels sprouts, cabbage, collards, horseradish, kale, kohlrabi, leek, mustard, onion, peas, potato, radish, rhubarb, spinach, turnip |
| Semi-hardy crops (tolerate a light frost) 2 to 4 weeks before the average last spring frost | April 16 to April 30 | Beet, carrot, cauliflower, celery, chard, Chinese cabbage, lettuce, mustard, parsnip |
| Tender crops (damaged by frost) after the average last spring frost, once nights stay above 50°F | From May 14 | Bean, sweet corn, tomato |
| Very tender crops (warm season) at least 2 weeks after the average last spring frost, once nights stay above 60 to 65°F | From May 28 | Cucumber, eggplant, melons, okra, pepper, pumpkin, squash, sweet potato |
Spring planting for direct seeding or transplants. A late cold snap can still happen, so watch the forecast and protect tender plants. Want today's answer for your ZIP code? Use what to plant now.
Sources: NOAA NCEI U.S. Climate Normals 1991 to 2020; Purdue Extension, Indiana Vegetable Planting Calendar (HO-186-W).
Choosing plants for zone 4b
When you shop, look for the hardiness range on the tag or in the catalog, such as "zones 4 to 9". Pick perennials, shrubs and trees whose range includes 4b. If you are set on a plant rated only to a warmer zone, plant it in a sheltered spot against a south-facing wall, mulch the roots before winter, or grow it in a container you can move into a garage. Zones only cover winter cold, so also check sun, water and soil needs. More in how to read a plant tag.
Duluth ZIP codes and zones
ZIP codes GeoNames assigns to Duluth, which can include PO box ZIP codes.
Other cities in Minnesota
Frequently asked questions
When is the last frost in Duluth?
The median last spring frost (32°F) near Duluth is May 14, and the median first fall frost is October 12, based on NOAA 1991 to 2020 climate normals.
What planting zone is Duluth in?
Duluth, MN is in USDA plant hardiness zone 4b (ZIP codes range from 4a to 5a). Zone 4b means an average coldest winter night of -25 to -20°F (-32 to -29°C), based on the 2023 USDA map.
Did Duluth's zone change in 2023?
The 2023 USDA map uses weather data from 1991 to 2020. The USDA says about half of the country shifted to the next warmer half zone compared with the 2012 map, while the rest stayed in the same half zone.
Zones: 2023 USDA Plant Hardiness Zone Map ZIP code listings, PRISM Climate Group, Oregon State University. Place names: GeoNames (CC BY 4.0). Not the official USDA map. Our data.