Plants grow best in specific locations due to the temperature and climate that they can tolerate. Across the country, temperatures can vary significantly from one coast to another, within the same state, or from one state to the next. When planting flowers it is important for people to understand what grows best where they live and what will likely not thrive at all. For this purpose there is a resource known as the USDA Plant Hardiness Zone Map. This map vertically divides the country into thirteen zones of hardiness for gardening in winter temperatures. The zones are based on the coldest annual minimum temperatures in a region based on averages over a period of thirty years. Each of the planting zones is numbered, with Zone 1 being the region with the coldest annual temperatures and Zone 13 being the hottest. Each zone on the map is separated by ten degrees Fahrenheit. Additionally, each zone is further broken down into "a" and "b" sub-zones that are divided by five degrees Fahrenheit. Understanding and following the gardening zones is one of the best ways to ensure a beautiful and healthy garden.
Zone 1 can be found in areas with extreme minimum temperatures of -50 degrees Fahrenheit or lower. Areas within this zone are further divided into 1a and 1b. The temperature range in zone 1a is between -60 and -55 degrees, while 1b is -55 to -50 degrees Fahrenheit. Parts of Alaska, including Bettles and North Slope, are zone 1. Plants such as the quaking aspen, dwarf birch and black crowberry will grow well in zone 1.
Zone 2 is another area with inhospitably cold temperatures, and is mapped with annual cold temperatures between -50 and -40 degrees Fahrenheit. People who live in this planting zone can successfully plant the American elm, American cranberry bush and the silverberry. Some plants do best in one of the specific growing zones. For example, bearberry is most successfully planted in zone 2b where the minimum temperature range is between -45 degrees Fahrenheit and -40 degrees Fahrenheit.
Zone 3 is an area that is known for relatively cold winters and short summers. Plants that can survive temperatures between -30 and -40 degrees Fahrenheit are suitable for this zone. Aster is a flower that will thrive here, as will black-eyed Susans and tulips. Areas in Alaska are zone 3 as are areas in North Dakota, Montana, Minnesota, and Wisconsin. Zone 3 is further divided in half into garden zones 3a and 3b.
This zone ranges from 30 to 20 degrees Fahrenheit with the last frost occurring in early June. Like Zone 3, the winters are cold while the summers are short. Plants that thrive in Zone 4 include the Japanese yew, ginkgo, the Trumpet Honeysuckle, and the Persian violet. Nebraska, Iowa, Illinois, and parts of New York and Maine are all parts of Zone 4.
Zone 5 is found in regions where the last frost occurs in late May and the lowest temperatures are between -20 and -10 degrees Fahrenheit. Sub-zones split these coldest temperatures, with 5a being -20 to -15 degrees Fahrenheit and 5b being -15 to -10 degrees Fahrenheit. Areas within this zone have winters that are cold and windy, and summers that tend to be long. Gardeners who are both casual and professional may plant plants such as the Japanese maple, Japanese holly, the multiflora rose, Shasta daisies, and tulips. Vegetables and fruits that grow well in this zone include spinach, strawberries and tomatoes.
In Zone 6, plants may safely tolerate temperatures of -10 to 0 degrees Fahrenheit. The summer weather conditions in Zone 6 are usually dry and long. The winters are often windy and very cold. This zone nearly bisects the country and is found in states such as New Mexico, Missouri, Illinois, Indiana, Kentucky, Ohio, and West Virginia. Other states including parts of Washington, Oregon, Nevada, Utah, Connecticut, New York, Pennsylvania, and Massachusetts are also Zone 6 to some extent. The last frost in these areas tends to be around mid-May. Plants and flowers that grow well in Zone 6 include the English lavender, purple coneflower, hydrangeas, English yew, English holly, and American holly.
Areas with lowest temperatures between 0 to 10 degrees Fahrenheit are known as Zone 7. Generally the last frost in these areas is in late April. Flowers and plants that thrive in this planting zone include the Kurume azalea, daffodils, crocuses, lilies and pansies. Plants that grow best in sub-zones include chinaberry, Monterey pine, and monkey puzzle, all of which grow best if temperatures reach no lower than 5 to 10 degrees Fahrenheit or 7b. On the map, Zone 7 is found in states that include, but are not limited to, Texas, Nevada, California, Washington, Oregon, and Virginia.
People living in Zone 8 are able to safely plant flowers and other plants that can tolerate low temperatures from 10 to 20 degrees Fahrenheit. People who live in subzone 8a may plant flowers in temperatures as low as 10 to 15 degrees Fahrenheit. People living in zone 8b can plant in minimum temperatures from 15 to 20 degrees Fahrenheit. Zone 8 covers much of the lower half of the U.S. and can be found in states such as California, Nevada, Arizona, Texas, Mississippi, Alabama, Georgia, Florida, and South Carolina, to name a few. Plants and flowers that are suitable for this zone include oleander, Indian azalea, hybrid rhododendron, butterfly blue, and purple-top verbena
Warm weather flowers and plants are suitable for planting in zone 9, where the annual minimum temperature is 20 to 30 degrees Fahrenheit. The gardening zones in zone 9 are zone 9a and 9b. Plants in zone 9a will tolerate minimum temperatures of no lower than 20 to 25 degrees Fahrenheit. In 9b, the lowest temperature for flowers or plants should be 25 to 30 degrees Fahrenheit. Zone 9 occupies most of the lower states including California, Arizona, Texas, and Florida, to name a few. Plants that are well suited for this area include fuchsias, asparagus-fern, Australian pine, and Chinese hibiscus.
Zone 10 gardeners are dealing with warmer temperatures that are not suitable for cold weather plants. The average minimum annual temperatures that plants can safely tolerate in these regions are 30 to 40 degrees Fahrenheit. The two planting zones that make up zone 10 are 10a and 10b. Examples of where these garden zones are found include California, parts of Arizona and East Texas, Louisiana, Florida, and some of the Hawaiian Islands. Bougainvillea, poinsettia, royal palm, and rubber plants all grow well in zone 10.
This is a tropical zone that is found in some areas of Southern California, the Florida Keys, the Hawaiian Islands and Puerto Rico. Annual minimum temperatures are between 40 and 50 degrees Fahrenheit. The growing zones in zone 11 include 11a and 11 b. Geraniums, impatiens, and veronica or speedwell, are flowers that do well within these zones.
According to the USDA Hardiness Zone Map, these garden zones apply to the Hawaiian Islands and Puerto Rico and are not found on mainland USA. Temperatures for zone 12 are 50 to 60 degrees Fahrenheit. Zone 13 temperatures are 60 to 70 degrees Fahrenheit. Each of the two zones has sub zones that split them by 5 degrees Fahrenheit. Musk okra, caterpillar plant, and knife acacia are flowers that grow in these zones.
Written By Ava Rose.