The United States Department of Agriculture created the Plant Hardiness Zone map in 1990 to assist farmers and gardeners in determining the plants best suited for their local growing area. Nurseries, plant catalogs, seed companies and gardening magazines use this map. The USDA Planting Zone Map of North America is divided into 11 zones, each 10 degrees Fahrenheit warmer in an average winter than the zone next to it. The dates are determined by lowest average winter temperature. There are also different frost dates and climate areas within each zone, due to local topographical conditions. Lakes, rivers, canyons and mountains each influence the immediate, local growing conditions.
Find Your Zone
Look at the USDA Plant Hardiness Zone Map to determine which planting zone you are in. Find the general area you live in.
Identify the local area you live in and determine which color band it is in. Each band of color corresponds to a color on the "Average Annual Minimum Temperature" chart at the right side of the map.
Find your color on the chart. It has a zone number and letter on the left and a temperature range on the right side of the chart. For instance, zone 8b has an average annual minimum temperature range of 15 to 20 degrees F.