USDA hardiness zone 4b
In zone 4b, the average annual extreme minimum temperature is -25 to -20°F (-31.7 to -28.9°C), based on 1991–2020 data from the 2023 USDA Plant Hardiness Zone Map.
What zone 4b means for your garden
A plant labeled "hardy to zone 4b" should survive a typical winter low of -25°F. Most perennials sold at garden centers are rated for this zone or colder; marginal plants rated one zone warmer can survive in sheltered spots. Zone 4a is the colder half of zone 4.
ZIP codes in zone 4b: 1,256 in contiguous U.S., 28 in Alaska. New to zones? Read how to read your hardiness zone.
Frost dates in zone 4b
Across 3 major cities in zone 4b, the 30%-risk last spring frost ranges from May 2 to May 22 (median May 5), and the first fall frost has a median of Oct 4. Frost timing depends on elevation, latitude and distance from water — a zone does not set a frost date, so check your city page for local dates.
Typical planting calendar for zone 4b
Based on the median frost dates above. For your exact dates, use your city page.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 10 – Mar 24 | May 12 – May 26 | — | — |
| Pepper | Feb 24 – Mar 10 | May 19 – Jun 2 | — | — |
| Lettuce | Mar 24 – Apr 7 | Apr 21 – May 12 | Apr 7 – May 19 | Jul 26 – Aug 23 |
| Green Beans | — | — | May 12 – Jun 16 | Jul 12 – Jul 26 |
| Sweet Corn | — | — | May 12 – Jun 9 | — |
| Zucchini & Summer Squash | Apr 7 – Apr 14 | May 12 – May 26 | May 12 – Jun 2 | Jul 12 – Jul 26 |
| Cucumber | Apr 7 – Apr 14 | May 19 – May 26 | May 12 – Jun 2 | Jul 12 – Jul 26 |
| Carrot | — | — | Apr 14 – May 19 | Jul 12 – Jul 26 |
| Onion | Feb 10 – Feb 24 | Apr 7 – Apr 21 | — | — |
| Potato | — | Apr 7 – Apr 28 | — | — |
| Basil | Mar 24 – Apr 7 | May 19 – Jun 2 | May 19 – Jun 9 | — |
| Spinach | — | — | Mar 24 – Apr 21 | Aug 9 – Sep 6 |
| Kale | Mar 10 – Mar 24 | Apr 7 – Apr 28 | Apr 7 – Apr 28 | Jul 26 – Aug 23 |
| Broccoli | Mar 10 – Mar 24 | Apr 21 – May 12 | — | Jul 12 – Jul 26 |
| Peas | — | — | Mar 24 – Apr 14 | Jul 26 – Aug 9 |
| Eggplant | Feb 24 – Mar 10 | May 19 – Jun 2 | — | — |
| Cabbage | Mar 10 – Mar 24 | Apr 7 – Apr 21 | — | Jul 12 – Jul 26 |
| Radish | — | — | Mar 31 – May 19 | Aug 23 – Sep 20 |
| Strawberry | — | Apr 7 – Apr 28 | — | — |
| Beets | — | — | Apr 14 – May 26 | Jul 26 – Aug 9 |
Cities in zone 4b (3)
Major cities whose center falls in zone 4b:
- Rochester, MN — last frost May 5, first frost Oct 1
- Duluth, MN — last frost May 22, first frost Oct 5
- Lakeville, MN — last frost May 2, first frost Oct 4
← Zone 4a · Zone 5a → · All zones
Zone 4b questions
How cold does it get in zone 4b?
Zone 4b is defined by an average annual extreme minimum temperature of -25 to -20°F (-31.7 to -28.9°C) for 1991–2020 — the average of each year's single coldest night, not the record low. Individual winters can be colder, so plants rated exactly for zone 4b carry some risk in a severe year.
When is the last frost in zone 4b?
It depends far more on the city than on the zone. Among 3 zone 4b cities on this site, the 30%-risk last spring frost runs from May 2 in Lakeville, MN to May 22 in Duluth, MN — 20 days apart (median May 5).
Which states have zone 4b?
The 2023 listings put 1,284 ZIP codes in zone 4b, spread over 15 states and territories. The most are in Minnesota (336), Wisconsin (238), South Dakota (184), Montana (129), New York (107).
Did zone 4b grow on the 2023 map?
No: 1,890 ZIP codes were in zone 4b on the 2012 map and 1,284 are on the 2023 map (-606). Of today's zone 4b ZIP codes that were also listed in 2012, 39% were in a colder zone then, 60% were already 4b, and 1% were in a warmer zone. What changed in 2023.
Which big cities are in zone 4b?
The largest cities on this site in zone 4b are Rochester, MN, Duluth, MN, Lakeville, MN; 3 cities in all are listed below.