What zone 10a means
In zone 10a, the average of the coldest night of each winter (1991 to 2020) is 30 to 35°F (-1 to 2°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 10a, 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 10a next to its neighbors
Zone 9b, one half zone colder, averages 25 to 30°F (-4 to -1°C). Zone 10b, one half zone warmer, averages 35 to 40°F (2 to 4°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 9b are now in 10a.
Using zone 10a when you shop
Look for the hardiness range on plant tags and in catalogs. A plant listed for "zones 8 to 12" includes zone 10a. 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 10a ZIP codes
Cities in zone 10a
Frequently asked questions
What does zone 10a mean?
Zone 10a covers places where the average coldest winter night is 30 to 35°F (-1 to 2°C). On the 2023 USDA map, 1,234 ZIP codes are in zone 10a.
What is the difference between zone 10a and 10b?
Each 10°F zone is split into two 5°F half zones. "a" is the colder half and "b" the warmer half. Zone 10a averages 30 to 35°F (-1 to 2°C); zone 10b averages 35 to 40°F (2 to 4°C).
Source: 2023 USDA Plant Hardiness Zone Map ZIP code listings, PRISM Climate Group, Oregon State University; USDA ARS. Not the official USDA map.