The Map Moved Under My Feet
Did you feel that? It felt like the earth moved under my feet. Actually, it was a shift in climate, as marked by the 2012 USDA Plant Hardiness Zone Map. The PHZM (Plant Hardiness Zone Map) is the guide gardeners use to decide what plants will likely grow, or not, in our yards. The 2012 version of the PHZM shows that the hardiness zone lines have shifted for most of the U.S. My home has shifted from Hardiness Zone 5b (1990 map) and is now solidly in Hardiness Zone 6b (2012 map) which is 10°F. warmer.
According to the USDA - 'Compared with the 1990 version, zone boundaries in this edition of the map have shifted in many areas. The new PHZM is generally one half-zone warmer than the previous PHZM throughout much of the United States, as a result of a more recent averaging period (1974–1986 vs. 1976–2005). However, some of the changes in the zones are the results of the new, more sophisticated mapping methods and greater numbers of station observations used in this map, which has greatly improved accuracy, especially in mountainous regions. These changes are sometimes to a cooler, rather than warmer, zone.'
What this means is that many gardeners will need to re-evaluate which plants will grow best around their homes. Certain plants that were already at the extreme warm end of their range may no longer be suitable with the shift in climate. Of course, this change will also allow gardeners to try new plants which need warmer conditions. Either way, gardeners should double-check their current hardiness zone while browsing seed catalogs and planning their spring planting.
PlantMaps.com - Interactive Hardiness Zones Map (1990 data)