According to the 2023 USDA Hardiness Zone Map St. Marys County, Maryland is in Zones 7b (5°F to 10°F), 8a (10°F to 15°F) and 8b (15°F to 20°F). This is a change from the 2012 USDA Hardiness Zone Map which has St. Marys County in Zones 7a (0°F to 5°F) and 7b (5°F to 10°F).