These charts are generally used to determine what garden and landscape plants you can grow in your garden and around your home. They determine whether or not the plants will survive the climate in your area. The USDA Plant Hardiness Zone Map factors in average winter minimum temperatures. Unfortunately, winter does not always follow the averages in these charts. These charts and maps start with Zone 1, where minimum temperatures can go down to MINUS 50 degrees Fahrenheit, and ranges to Zone 11, for the fortunate plant growers in Hawaii and extreme Southern Florida where lows don't normally drop below 40 degrees Fahrenheit. Although Hawaii is rarely affected by "Arctic Expresses" dropping down from the north, Florida sometimes is. The data on which the USDA plant hardiness zone map is based was gathered over a period of 60 years. In the northern U.S. and Canada, the growing season usually means the days between last and first frost, or approximately the last and first occurrence of 0° C/32° F (freezing) overnight low temperature. This is roughly May to October.