In the state of Kentucky, USDA zones 6 through 7 are represented. Louisville falls in zone 7, although some gardeners have luck with warmer weather plants. For example, I've seen fig trees thriving when planted in direct sunlight. Figs are normally a tree grown in zones 8-10.
Understanding USDA Zones
Essentially, USDA zones are areas delineated by temperature. The goal is to distinguish which areas certain plants can thrive in based on the vegetation's hardiness. The zones give landscapers and gardeners a guide to follow when planting trees, flowers, fruits or vegetables. Each zone is a geographically defined area marked by the minimum temperatures of that zone, measured in Celsius. For example, if a plant is described as "hardy to zone 10," it is assumed the plant can thrive as long as the temperature does not fall below -1°C (or 30°F).
Louisville is in a cooler zone, so a plant that is "hardy to zone 7" could succeed in an area with an annual low temperature of around -17°C (or 10°F). The USDA zone system was developed by the United States by the Department of Agriculture (USDA).
Of course, weather varies. Keeping Louisville's annual high and low temperatures in mind, along with our USDA zone, can help to ensure gardening success.