On the previous map, most of Ohio – from the river on the south to the lake on the north – was in Zone 6a, with the average lowest temperature ranging from -10 to -5 degrees Fahrenheit.

Ohio largely transitioned from Zone 5 to a warmer Zone 6 over that time. But Daly said the 1990 map, which he did not work on, relied on data over a shorter time period that was also unusually cold.

On the revised 2023 map, about half of Ohio is in Zone 6b, where the average low temperature range is -5 to 0 degrees Fahrenheit. The other half of Ohio is now in Zone 6a, where the average low ...