Horticulturists are interested in macroclimatic and microclimatic variation across space and through time, and the degree to which the range limits of plants correspond with these changes. Southwest Ohio occurs across a climatic transition between cool and warm temperate climate regimes as defined by winter minimum temperatures. This study reviews changes across the transition as reflected in the boundaries between macroclimatic zones defined by Köppen, USDA, Sunset and Southern Living and relates these regional patterns to the successful propagation trials of two palm species, Sabal palmetto and Sabal minor. The study compares macroclimatic changes across the region for historical and current data and microclimatic data for five palm sites. Results show geographic shifts in the C-D Köppen boundary through time, depending on the time period and spatial resolution of the data. Microclimatic data for the palm sites further clarify the position of the tension zone, but survivorship data suggest a broader cold tolerance by palms across this region. These data, coupled with corresponding research in biotechnology, substantiate the potential for horticultural range expansion in ornamental palms.