Agribusiness Management Resources

Editorial-opinion "IT’S CLEAR at first glance that the draft version of the 2003 USDA Plant Hardiness Zone Map bears little resemblance to its most recent predecessor, the 1990 map."

Discussion of Conflicting Maps Opinion

Peer-reviewed-final form 28 July 2010 "Trends in the [Plant Hardiness] PH statistic over the past 30 years, estimated by 1976–90 versus 1991–2005 difference maps, indicate that the frequency of extreme cold events has decreased across much of the conterminous United States. The PH statistic generally warmed at least one half zone, with a warming of two half zones occurring over large parts of the central and eastern United States, as well as the Pacific Northwest."

Peer-reviewed: "... 50-year updates for two plant hardiness models (maps)... Species-specific climate envelope models are an alternative to generalized hardiness zones. We generated climate envelopes for 62 northern tree species over the same 50-year interval and found an average northward shift of 57 kilometers."

The 1990 USDA map used data from 1974 to 1986, a 12 year average, with 4 years to publication.

Full size 1990 map: planthardiness.ars.usda.gov/PHZMWeb/Images/USZoneMap.jpg

The 2006 Arbor Day map used data from 1990 to 2005, a 15 year average, with 1 year to publication.

Full size Arbor Day foundation map: www.arborday.org/media/zones.cfm

The 2012 USDA map used data from 1976 to 2005, a 30 year average, with 7 years to publication.

Full size 2012 map: www.planthardiness.ars.usda.gov

Alternative source for image: https://commonsensehome.com/plant-hardiness-zones-microclimate/