<P> A hardiness zone is a geographically defined area in which a specific category of plant life is capable of growing, as defined by climatic conditions, including its ability to withstand the minimum temperatures of the zone (see the scale on the right or the table below). For example, a plant that is described as "hardy to zone 10" means that the plant can withstand a minimum temperature of - 1 ° C (30.2 ° F) to 3.9 ° C (39.0 ° F). First developed by the United States Department of Agriculture (USDA) as a rough guide to landscaping and gardening, the use of the zones has been adopted by other countries . </P> <P> In the United States, most of the warmer zones (zones 8, 9, 10, and 11) are located in the southern half of the country and on the Pacific coast . The low latitude and often stable weather in Florida, the Gulf Coast, and southern Arizona and California, are responsible for the few episodes of severe cold relative to normal in those areas . The more northerly and central portions of the USA have the cooler zones (zones 7, 6, 5, and 4). The central and northerly portions of the mainland often have much less consistent range of temperatures in winter due to being more continental, and thus the zone map has its limitations in these areas . </P> <Table> <Tr> <Td_colspan="2"> Zone </Td> <Td> From </Td> <Td> To </Td> </Tr> <Tr> <Td> 0 </Td> <Td> </Td> <Td_colspan="2"> <− 53.9 ° C (− 65 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 53.9 ° C (− 65 ° F) </Td> <Td> − 51.1 ° C (− 60 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> − 51.1 ° C (− 60 ° F) </Td> <Td> − 48.3 ° C (− 55 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 48.3 ° C (− 55 ° F) </Td> <Td> − 45.6 ° C (− 50 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> − 45.6 ° C (− 50 ° F) </Td> <Td> − 42.8 ° C (− 45 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 42.8 ° C (− 45 ° F) </Td> <Td> − 40 ° C (− 40 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> − 40 ° C (− 40 ° F) </Td> <Td> − 37.2 ° C (− 35 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 37.2 ° C (− 35 ° F) </Td> <Td> − 34.4 ° C (− 30 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> − 34.4 ° C (− 30 ° F) </Td> <Td> − 31.7 ° C (− 25 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 31.7 ° C (− 25 ° F) </Td> <Td> − 28.9 ° C (− 20 ° F) </Td> </Tr> <Tr> <Td> 5 </Td> <Td> </Td> <Td> − 28.9 ° C (− 20 ° F) </Td> <Td> − 26.1 ° C (− 15 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 26.1 ° C (− 15 ° F) </Td> <Td> − 23.3 ° C (− 10 ° F) </Td> </Tr> <Tr> <Td> 6 </Td> <Td> </Td> <Td> − 23.3 ° C (− 10 ° F) </Td> <Td> − 20.6 ° C (− 5 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 20.6 ° C (− 5 ° F) </Td> <Td> − 17.8 ° C (0 ° F) </Td> </Tr> <Tr> <Td> 7 </Td> <Td> </Td> <Td> − 17.8 ° C (0 ° F) </Td> <Td> − 15 ° C (5 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 15 ° C (5 ° F) </Td> <Td> − 12.2 ° C (10 ° F) </Td> </Tr> <Tr> <Td> 8 </Td> <Td> </Td> <Td> − 12.2 ° C (10 ° F) </Td> <Td> − 9.4 ° C (15 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 9.4 ° C (15 ° F) </Td> <Td> − 6.7 ° C (20 ° F) </Td> </Tr> <Tr> <Td> 9 </Td> <Td> </Td> <Td> − 6.7 ° C (20 ° F) </Td> <Td> − 3.9 ° C (25 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> − 3.9 ° C (25 ° F) </Td> <Td> − 1.1 ° C (30 ° F) </Td> </Tr> <Tr> <Td> 10 </Td> <Td> </Td> <Td> − 1.1 ° C (30 ° F) </Td> <Td> + 1.7 ° C (35 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> + 1.7 ° C (35 ° F) </Td> <Td> + 4.4 ° C (40 ° F) </Td> </Tr> <Tr> <Td> 11 </Td> <Td> </Td> <Td> + 4.4 ° C (40 ° F) </Td> <Td> + 7.2 ° C (45 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td> + 7.2 ° C (45 ° F) </Td> <Td> + 10 ° C (50 ° F) </Td> </Tr> <Tr> <Td> 12 </Td> <Td> </Td> <Td> + 10 ° C (50 ° F) </Td> <Td> + 12.8 ° C (55 ° F) </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="2">> + 12.8 ° C (55 ° F) </Td> </Tr> </Table> <Tr> <Td_colspan="2"> Zone </Td> <Td> From </Td> <Td> To </Td> </Tr>

What is the difference between zone 8a and 8b
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