The
National Arbor Day Foundation has
recently completed an extensive
updating of U.S. Hardiness Zones
based upon data from 5,000 National
Climatic Data Center cooperative
stations across the continental
United States.
Because of global warming, the hardiness
zones have shifted north. Some places
have increased by 1 zone, some even
by 2. We were formerly zone 4 in
the 1990 map, and we are now
zone 5.
The hardiness zones divide the US
into 11 zones (1 the coldest and
11 the warmest), based on the average
minimum temperature. This information
helps you know which plants will
survive over the winter in your
area. For example if you live in
zone 5 and purchase a plant that
is rated for zone 7 (warmer), chances
are it won't survive over the winter.
Of course other factors come into
play such as how well it is protected
over the winter, and whether you
happen to have a micro-climate in
your yard. Plantings against a south
facing wall of your home often benefit
from a 1 or 2 zone boost.
