The climate of a particular region is based on annual average
high and low temperatures, annual rainfall, and the number
of frost-free days. Wind and altitude are modifiers. Linnaeus
said that altitude is more in accordance with the habitation of
plants than latitude or longitude. This is backed up by research
that found that plants growing in alpine regions are similar in
different parts of the world, whereas plants growing at the same
longitude or latitude are often different.
The USDA has generated climate maps that divide the country
into zones based on climate. The United States National
Arboretum Web site listed in the Further Reading section has
an interactive USDA Plant Hardiness Zone Map that you can
access to determine the zone for your region. It also provides
information on how to choose perennial plants that will survive
the winter in your area.