Most gardeners are familiar with the U.S. Department of Agriculture's Temperature Zone Map. The map is based on average annual minimum temperatures recorded throughout North America. If you are aware of the planting and temperature zones in your area, you can plan your garden accordingly, with the choice of plants and flowers that will thrive in these temperatures.
Temperature zone data entails a useful source of information for anyone who plants. It also provides information on soil fertility, moisture, humidity, drainage, wind and sun exposure and determines a plant’s growth or failure rate in a particular area.
Nowadays, hardiness zones for all kinds of plants are available online. For instance, if a type of plant or tree is said to be within zone 4 to 9, then it implies that the tree is known to be hardy in zones from 4 to 9. Suitable hardiness also means a plant is expected to grow in the zone's temperature extremes. This is dependent on local variations such as soil conditions, winds, moisture.
Most nursery magazines, reference catalogs and gardening handbooks describe plants that use USDA hardiness zones. A map of hardiness zones across America can be found on USDA’s website at www.usna.usda.gov/Hardzone.
Prior to deciding what kind of landscape or garden plants that you can grow in your place, you would need to first determine the temperature zones applicable in your area. The USDA Plant Hardiness Zone Map shows the average winter minimum temperatures that can be expected each year in the United States, Mexico and Canada. These temperatures recorded are identified as the average annual minimum temperatures, and are based on the lowest temperatures recorded. It begins with Zone 1, where the minimum temperatures is below minus 50 degrees Fahrenheit, and extends to Zone 11, where the temperature does not drop below 40 degrees Fahrenheit. Zone 11 is supposed to have an average annual minimum temperature of above 40 F (4.4 C) and that is essentially frost free.
Below is a list of zones and the territories that fall under each.
Zone Fahrenheit Celsius Cities
1 Less than -50F Less than -45.6C Northwest Territories (Canada); Alaska
2a -50F to -45F -42.8C to -45.5C Manitoba (Canada); Prudhoe Bay, Flin Fon
2b -45F to -40F -40.0C to -42.7C Unalakleet, Alaska; Pine creek
3a -40F to -35F -37.3C to -39.9C St. Michael, International Falls, Minnesota
3b -35F to -30F -34.5C to -37.2C Sidney, Montana; Tomahawk
4a -30F to -25F -31.7C to -34.4C Lewistown, Montana; St. Paul, Minnesota
4b -25F to -20F -28.9C to -31.6C Northwood, Iowa
5a -20F to -15F -26.2C to -28.8C Illinois; Des Moines, Iowa
5b -15F to -10F -23.4C to -26.1C Mansfield; Columbia, Missouri
6a -10F to -5F -20.6C to -23.3C Lebanon, Pennsylvania; St. Louis, Missouri
6b -5F to 0F -17.8C to -20.5C Branson, Missouri; McMinnville, Tennessee
7a 0F to 5F -15.0C to -17.7C South Boston, Virginia; Oklahoma City
7b 5F to 10F -12.3C to -14.9C Arkansas; Griffin
8a 10F to 15F -9.5C to -12.2C Tifton; Dallas
8b 15F to 20F -6.7C to -9.4C Gainesville; Austin, Texas
9a 20F to 25F -3.9C to -6.6C St. Augustine; Houston, Texas
9b 25F to 30F -1.2C to -3.8C Fort Pierce; Brownsville, Texas
10a 30F to 35F 1.6C to -1.1C California; Naples, Florida
10b 35F to 40F 4.4C to 1.7C Coral Gables; Miami, Florida
11 Above 40F Above 4.5C Mexico; Honolulu, Hawaii
The most important information is to determine whether your garden plants would survive the local climate in your area. By using the USDA Plant Hardiness Zone Map to find the zone in which they live, gardeners are able to ascertain what plants will withstand the average minimum temperatures.