According to the 2023 USDA Hardiness Zone Map Cowlitz County, Washington is in Zones 7b (5°F to 10°F), 8a (10°F to 15°F) and 8b (15°F to 20°F). There is no change from the 2012 USDA Hardiness Zone Map which has Cowlitz County in also in Zones 7b (5°F to 10°F), 8a (10°F to 15°F) and 8b (15°F to 20°F).