Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Zone 4a

In USDA zone 4a the coldest night of an average winter reaches −30 to −25 °F (−34.4 to −31.7 °C). 814 ZIP codes (2.0% of all) are in this zone.

Zone4a−30 to −25 °F
Coldest night−34.4 to −31.7 °C
ZIP codes814
Typical last frostMay 12
Typical first frostSep 28

Frost dates vary within zone 4a

For the middle half of zone-4a ZIP codes the last spring frost falls between May 9 and May 19, and the first fall frost between Sep 24 and Oct 1. The zone measures winter cold, not season length: humid Eastern and dry Western towns in the same zone can be weeks apart. Use your ZIP code for a planting date.

States with zone 4a

North Dakota316 ZIPsMinnesota200 ZIPsWisconsin73 ZIPsMontana71 ZIPsAlaska31 ZIPsNew York29 ZIPsMaine26 ZIPsSouth Dakota24 ZIPsMichigan13 ZIPsVermont11 ZIPsWyoming10 ZIPsNew Hampshire5 ZIPsColorado2 ZIPsIdaho2 ZIPsUtah1 ZIPs

Cities mostly in zone 4a

Fargo, ND13 ZIPsBismarck, ND7 ZIPsGrand Forks, ND5 ZIPsGrand Rapids, MN3 ZIPsMoorhead, MN3 ZIPsWahpeton, ND3 ZIPsMinot, ND3 ZIPsWilliston, ND3 ZIPsDetroit Lakes, MN2 ZIPsFergus Falls, MN2 ZIPsAberdeen, SD2 ZIPsGrand Forks Afb, ND2 ZIPs

← Zone 3b (colder)Zone 4b (warmer) →

Questions

What is the temperature range of zone 4a?

Zone 4a covers places where the coldest night of an average winter (the annual extreme minimum averaged over 1991–2020) is −30 to −25 °F, or −34.4 to −31.7 °C.

When is the last frost in zone 4a?

Across ZIP codes in zone 4a, the median last spring frost falls between May 9 and May 19 for the middle half of places. Zone alone doesn't set the frost date — check your ZIP code.

Which states have zone 4a?

Zone 4a occurs in 15 states; the most ZIP codes are in North Dakota, Minnesota, Wisconsin, Montana, Alaska.

What can I grow in zone 4a?

Perennials, shrubs and trees labeled hardy to zone 4a or a lower (colder) number should survive a typical winter. Annual vegetables depend on frost dates rather than zone.

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.