Gardening Temperature Zones

Many countries have devised plant hardiness zoning systems to help horticulturalists and gardeners identify plants suited for their climates. The U.S. Department of Agriculture Plant Hardiness Zone Map provides vegetable and flower growers guidance based on minimum winter temperatures.

USDA Hardiness Zones

• The USDA took an average of the lowest annual temperatures over 10 years and scaled the zones by 10 degrees Fahrenheit. The result was 11 zones. They then further subdivided Zones 2 to 11 into a and b, creating 20 subzones. These are known as plant hardiness zones. Florida, for example, is Zone 10, and Alaska is Zone 1. This is not the only map used, but it is the most common. The American Horticultural Society uses a heat zone system.

Planting by Zones

• Tropical plants grow well in Zone 10. palmtrees in tropical labirint image by John Hofboer from Fotolia.com

  Plants are categorized by the zones in which they will successfully grow, so you may use the map a handy guide for buying seeds and plants suited to your area, particularly if you are buying plants away from home or seeds from a catalog. If you are a new gardener, your local nursery will know the zone in which you reside. The USDA Plant Hardiness Zone Map is widely available on the Internet.

Variations Within Zones

• A temperate garden. Garden image by Chad Perry from Fotolia.com

  The USDA Plant Hardiness Zone Map is a good start when planning your garden, but it does not provide information specific to localities. It's a good idea to note rainfall, heat extremes, humidity and your own particular microclimate as every location differs, even within sub-zones. The USDA map has been criticized as being inaccurate for regions west of the 100th meridian---which roughly divides the eastern and western United States---and for Texas.