Zones / 3b

Zone 3b

In the 2023 PRISM ZIP table, zone 3b is labeled with an average annual extreme minimum of -35°F to -30°F. 204 ZIP codes carry that half-zone. USDA’s map page describes these bands as 5°F half-zones inside 10°F zones.

None of the cities on this site fall in zone 3b. ZIP lookups still use it where the PRISM file says so.

Source: PRISM 2023 PHZM ZIP CSV and USDA Plant Hardiness Zone Map.