USGrowersGuide

Lookup · USDA 2023 map

Hardiness zone by ZIP code

Type a ZIP code to get its zone on the 2023 USDA Plant Hardiness Zone Map — the half zone, like 7b, and the winter low it stands for — plus the last and first frost dates from the nearest NOAA weather station, where one is within 100 km.

Works for all 40,502 US ZIP codes. Freeze dates need a NOAA station within 100 km; where there is none, the page says so rather than estimating one.

The scale

What each zone means

Each half zone is a 5 °F band of the average coldest winter night. The count is how many US ZIP codes the 2023 map puts in each one.

ZoneAverage coldest nightZIP codes
1a −60 to −55 °F 5
1b −55 to −50 °F 11
2a −50 to −45 °F 27
2b −45 to −40 °F 17
3a −40 to −35 °F 23
3b −35 to −30 °F 230
4a −30 to −25 °F 814
4b −25 to −20 °F 1,284
5a −20 to −15 °F 2,426
5b −15 to −10 °F 2,880
6a −10 to −5 °F 5,187
6b −5 to 0 °F 5,271
7a 0 to 5 °F 4,877
7b 5 to 10 °F 3,855
8a 10 to 15 °F 3,430
8b 15 to 20 °F 3,379
9a 20 to 25 °F 2,199
9b 25 to 30 °F 2,085
10a 30 to 35 °F 1,234
10b 35 to 40 °F 752
11a 40 to 45 °F 205
11b 45 to 50 °F 16
12a 50 to 55 °F 30
12b 55 to 60 °F 137
13a 60 to 65 °F 102
13b 65 to 70 °F 26

Questions

Common questions

What does a hardiness zone mean?

A USDA hardiness zone is the average coldest night of the year — the average annual extreme minimum temperature — over 1991–2020. Each zone covers 10 °F and is split in two: 7a is the colder 5 °F of zone 7 and 7b the warmer. It is an average, not the coldest it has ever been, and it says nothing about summer heat, rain or frost dates.

What changed between the 2012 and 2023 maps?

The 2023 map averages 1991–2020 where the 2012 map averaged 1976–2005. USDA says the new map is generally about one quarter-zone warmer than the 2012 map across much of the United States, that some changes come from more stations and better mapping methods rather than warmer winters, and that some places moved to a cooler zone. It used data from 13,625 stations. USDA also says a changed zone is no reason to remove plants that are doing well. This site does not hold the 2012 ZIP table, so it cannot tell you whether your own ZIP code changed.

Why does my ZIP code show a zone but no frost dates?

Every one of the 40,502 ZIP codes on the map has a zone, but 7,108 have no NOAA station within 100 km to take frost dates from. 7,027 of those are PO boxes and single delivery points with no published location at all; 81 are real places more than 100 km from a station. For those the answer says which case applies instead of borrowing a distant station’s dates.

Where do the frost dates come from?

From NOAA’s 1991–2020 climate normals, at the station nearest the middle of your ZIP code — 11.9 km away for the typical ZIP. The answer names the station and its distance. The dates are medians: in half of years the last spring freeze comes later than the date shown, and the first fall freeze earlier.

A zone is a winter measurement, not a planting date — why a hardiness zone is not a planting date.

Fall planting with your zone: When to Plant Garlic by Zone: Fall Dates for Zones 3–10; When to Plant Fall Bulbs by Zone: Tulips, Daffodils, More; and When to Plant Trees and Shrubs in Fall, by Zone.

By state

Hardiness zones by state

Every state page shows how its ZIP codes split across zones, with its frost-date range and the weather stations behind it.

Sources

Where the answer comes from

Zones: USDA Plant Hardiness Zone Map, 2023. Agricultural Research Service, U.S. Department of Agriculture (planthardiness.ars.usda.gov). The ZIP code table is the one PRISM Climate Group at Oregon State University publishes for the map (prism.oregonstate.edu/phzm), 40,502 ZIP codes including Alaska, Hawaii and Puerto Rico, shown unaltered.

Frost dates: NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, the median (P50) date of the last spring and first fall freeze at 32 °F, from 7,125 stations that publish them.

Pages for your area: the state link in an answer goes to the state page that lists that ZIP code. Arizona ZIP codes also link to the pages built from the University of Arizona Cooperative Extension calendar for their county.

A ZIP code covers an area, and a zone can change inside it, especially in hills. USDA’s own map is drawn on a half-mile grid; for a single address, check it there.