From the USDA: "The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones."
Visit the USDA site for an interactive GIS map clickable for all states: CLICK HERE
The map below shows zones as designated by the United States Department of Agriculture and can be used to determine the best time to plant and work on various gardening activities.
When to Plant