Zones for Growing Plants & Flowers

When gardeners refer to "growing zones" for plants and flowers, they are referring to the U.S. Department of Agriculture plant hardiness zones. The USDA divides the United States, Canada and Mexico into 11 zones based on factors including average winter and summer temperatures and rainfall. Using a hardiness zone map can be useful for gardeners, as it provides a nationally recognized method of classifying plants and flowers that helps them to select the ones that are most likely to grow in their region.

Hardiness zones 1 through 4 range from an average annual minimum of less than minus 50 degrees Fahrenheit to minus 20 F. In addition to the majority of Canada, states in these zones include Alaska, Minnesota, Wisconsin, Montana, Iowa and Nebraska. Plants that grow in these zones are considered as fully hardy to hardy and are generally woody, self-seeding plants such as birches, junipers and privets.

Zones 5 to 8 are in the range of minus 20 F to 20 F. Iowa, Illinois, Missouri, Pennsylvania, Oklahoma, Arkansas and Georgia lie within these zones and provide adequate growing conditions for a wide variety of flowers and plants including roses, azalea, holly and orange trees.

Zones 9 through 11 have an average minimum temperature of 20 F and above, with zone 11 being 40 F and above. States that lie in zones 9 through 11 include Texas, Florida, California and Hawaii; most of Mexico contains a mixture of these zones. Plants and flowers that thrive in this environment include citrus trees such as orange, lemon and lime and hardy plants such as gum trees, palms and rubber plants.

Although the USDA hardiness zones are useful for selecting plants that are likely to succeed in your area, the National Gardening Association points out some downfalls to the zone allocation process. The zones do not take into consideration soil drainage, freeze-thaw cycles, elevation and precipitation.