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Many garden plants have minimum temperature requirements, and are unable to survive winter temperatures below a given threshold. In recent decades, winters have been warming at many U.S. locations, with implications for gardeners and landscapers.
Planting zones are based on the 30-year average of the coldest day of the year at each location between 1971-2000 and 1981-2010, based on Global Historical Climatology Network-Daily data from NOAA’s National Centers for Environmental Information (NCEI). They are not the same as the USDA Plant Hardiness Zone maps.
The averages for each 30-year period were sorted into 10°F bins ranging from -40°F to 40°F. Then values were gridded to create continuous zones in which plants would be likely to face similar winter minimum temperatures. The 1971-2000 map was “subtracted” from the 1981-2010 map to show areas that are in a warmer zone now than they used to be.
Warmer zones are colored darker green, and cooler zones are colored paler green. Gray areas did not change zones. (That doesn’t mean they didn’t warm; only that any warming they may have experienced did not push them into a new 10° bin).
Because winters are getting warmer in many places, climate-related planting zones shifted northward and upward in elevation. For example, areas of central North Carolina that were previously in Zone 7 (average coldest temperature between 0 and 10°F) are now in Zone 8 (average coldest temperature between 10° and 20°F°).
These maps were produced in 2011 by Russell Vose of NCEI and NOAA Climate.gov as part of the communication and outreach that accompanied the release of the latest U.S. Climate Normals. Updated each decade, the U.S. Climate Normals are 30-year averages of many pieces of weather information collected from thousands of weather stations nationwide.
Each time the official Normals are updated, the earliest decade is dropped, and the most recent decade is added. With the 2011 update, the 1970s were dropped, and the 2000s were added. These planting-zone maps were created to illustrate how some of the climate variables that underpin the U.S. Climate Normals would be changing as the 30-year period shifted from 1971-2000 to 1981-2010.
Many garden plants have minimum temperature requirements, and are unable to survive winter temperatures below a given threshold. In recent decades, winters have been warming at many U.S. locations, with implications for gardeners and landscapers.
Planting zones are based on the 30-year average of the coldest day of the year at each location between 1971-2000 and 1981-2010, based on Global Historical Climatology Network-Daily data from NOAA’s National Centers for Environmental Information (NCEI). They are not the same as the USDA Plant Hardiness Zone maps.
The averages for each 30-year period were sorted into 10°F bins ranging from -40°F to 40°F. Then values were gridded to create continuous zones in which plants would be likely to face similar winter minimum temperatures. The 1971-2000 map was “subtracted” from the 1981-2010 map to show areas that are in a warmer zone now than they used to be.
Warmer zones are colored darker green, and cooler zones are colored paler green. Gray areas did not change zones. (That doesn’t mean they didn’t warm; only that any warming they may have experienced did not push them into a new 10° bin).
Because winters are getting warmer in many places, climate-related planting zones shifted northward and upward in elevation. For example, areas of central North Carolina that were previously in Zone 7 (average coldest temperature between 0 and 10°F) are now in Zone 8 (average coldest temperature between 10° and 20°F°).
These maps were produced in 2011 by Russell Vose of NCEI and NOAA Climate.gov as part of the communication and outreach that accompanied the release of the latest U.S. Climate Normals. Updated each decade, the U.S. Climate Normals are 30-year averages of many pieces of weather information collected from thousands of weather stations nationwide.
Each time the official Normals are updated, the earliest decade is dropped, and the most recent decade is added. With the 2011 update, the 1970s were dropped, and the 2000s were added. These planting-zone maps were created to illustrate how some of the climate variables that underpin the U.S. Climate Normals would be changing as the 30-year period shifted from 1971-2000 to 1981-2010.