[NAFEX] revised cold hardiness zones

Hal Love lovehd at comcast.net
Mon May 17 11:48:34 EDT 2004

Just took a look at the draft of the 2003 USDA Plant Hardiness Zone Map.
Seems a little behind schedule getting out, since its now 2004, but since I
did not see any mention of this in the archives, I thought it would be of
interest to this group.

Descriptions of the new map can be found here,

Here is a portion of the information from the link above.
"The updated USDA hardiness map shows in detail the lowest temperatures that
can be expected each year in the United States. These temperatures-referred
to as "average annual minimum temperatures"-are based on the lowest average
temperatures recorded for each of the winter seasons from 1987 to 2001.

The 2003 edition of the USDA hardiness map has 15 zones (four more than the
1990 version of the map), each of which represents a 10 degree Fahrenheit
(F) difference in average annual minimum temperature. The expansion of the
map to 15 zones is making it possible for the first time to assign hardiness
codes to sub-tropical and tropical plants, which previously had to be listed
by the minimum temperatures at which they would survive.

The "a" and "b" intra-zone divisions used on the 1990 map have been

".....Unlike previous maps, the 2003 map was created digitally. "It has a
higher level of resolution and shows smaller areas of change called
microclimates," says AHS President Emeritus Dr. H. Marc Cathey, who
coordinated development of the updated map. "These microclimates include
warmer areas around major cities, which tend to hold more heat because they
have a high density of buildings and large areas of concrete and blacktop.
You can also see cooler areas that may indicate higher elevations."

The new map reflects the current warming trend and there is significant
northward drift of the zones from the 1990 map. Based on the new map, I am
now right in the middle of zone 7 (The "Rose Zone"), whereas before, I was
in zone 6b. Here is a direct link to the pdf version of the map (5.57 mb).



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