What zone 12a means
In zone 12a, the average of the coldest night of each winter (1991 to 2020) is 50 to 55°F (10 to 13°C). Some winters will be colder than that and some milder: the zone is an average, not the coldest temperature ever recorded. When a plant tag lists a zone range that includes 12a, the plant should survive a typical winter here. If you are in the "a" half, you are in the colder part of the zone.
Zone 12a next to its neighbors
Zone 11b, one half zone colder, averages 45 to 50°F (7 to 10°C). Zone 12b, one half zone warmer, averages 55 to 60°F (13 to 16°C). On the 2023 map, about half the country moved to the next warmer half zone compared with 2012, so some gardens that were in 11b are now in 12a.
Using zone 12a when you shop
Look for the hardiness range on plant tags and in catalogs. A plant listed for "zones 10 to 13" includes zone 12a. If the range stops just above you, choose a sheltered spot, mulch roots before winter or grow it in a pot. Remember that zones describe winter cold only; heat, rainfall and soil decide the rest. How to read a plant tag.
States with the most zone 12a ZIP codes
Frequently asked questions
What does zone 12a mean?
Zone 12a covers places where the average coldest winter night is 50 to 55°F (10 to 13°C). On the 2023 USDA map, 30 ZIP codes are in zone 12a.
What is the difference between zone 12a and 12b?
Each 10°F zone is split into two 5°F half zones. "a" is the colder half and "b" the warmer half. Zone 12a averages 50 to 55°F (10 to 13°C); zone 12b averages 55 to 60°F (13 to 16°C).
Source: 2023 USDA Plant Hardiness Zone Map ZIP code listings, PRISM Climate Group, Oregon State University; USDA ARS. Not the official USDA map.