Plant Hardiness Zones Updated

The USDA has released an updated plant hardiness zone map, based on climate data from the past 30 years. The map, based on average minimum winter temperatures, is used by gardeners and growers to determine which plants will thrive at a given location. It was last updated in 1990. In addition to better representing our current climate, the new zones are also more precise, accounting for subtle elevation changes, urban heat islands and effects from bodies of water. Not surprisingly, warmer zones are creeping northward.

Lemon & orange grove on Route 46 near Cambria, CA. Photo: author

Interesting microclimates show up if you view the individual state maps (also a new feature). Urban heat islands push some metro areas into the next warmest zone, including Charleston, SC and Philadelphia. The Great Lakes have a counterintuitive warming effect in Ohio, making Cleveland better for growing things than Columbus. Probably the most dramatic contrast is the transect from California's Central Valley to the Sierra Nevada to the east, representing most of the hardiness zones of the Lower 48.

I'm amazed by how warm the Pacific Northwest is, though the January camelia blooms visible outside my window attest to our mild winters. Portland and Seattle are in the same hardiness zone as the Florida Panhandle. Perhaps I should try citrus farming.

Thanks to Zone 6b residents Bryan Cope and Drew Sonntag for sharing this news.

Link: http://planthardiness.ars.usda.gov/PHZMWeb/?loc=interstitialskip#