What zone 13b means
In zone 13b, the average of the coldest night of each winter (1991 to 2020) is 65 to 70°F (18 to 21°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 13b, 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 13b next to its neighbors
Zone 13a, one half zone colder, averages 60 to 65°F (16 to 18°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 13a are now in 13b.
Using zone 13b when you shop
Look for the hardiness range on plant tags and in catalogs. A plant listed for "zones 11 to 13" includes zone 13b. 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.
Frequently asked questions
What does zone 13b mean?
Zone 13b covers places where the average coldest winter night is 65 to 70°F (18 to 21°C). On the 2023 USDA map, 26 ZIP codes are in zone 13b.
What is the difference between zone 13a and 13b?
Each 10°F zone is split into two 5°F half zones. "a" is the colder half and "b" the warmer half. Zone 13a averages 60 to 65°F (16 to 18°C); zone 13b averages 65 to 70°F (18 to 21°C).
Source: 2023 USDA Plant Hardiness Zone Map ZIP code listings, PRISM Climate Group, Oregon State University; USDA ARS. Not the official USDA map.