The revised National Arbor Day Foundation 2006 Hardiness Zone Map
In 2006 the National Arbor Day Foundation published its own revised map using data that showed winter lows increasing as much as eight degrees warmer in some places. According to the foundation, the old zones have marched alarmingly northward.
Louise Ducote writing in the March | April 2009 issue of Orion Magazine about the USDA's resistance to replacing their 1990 hardiness zone map, drawn from data gathered from 1974 to 1986, with one that relies on more recent data regarding temperatures in the U.S.
