Hardiness Zone Map
from ArborDay.org
The 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.
- See a map highlighting changes between 1990 and 2006.
- See an animation that shows changes between 1990 and 2006.
- Find your hardiness zone.
- See a map of Alaska and Hawaii.
- See suggested trees for your region.
The U.S. Department of Agriculture's Cold Hardiness Zone Map was first published in 1960 and updated in 1990. It is based on average annual minimum temperatures recorded throughout North America. By using the map to find the zone in which you live, you can determine which plants will "winter over" in your garden because they can withstand these average minimum temperatures.
Although these zones are useful as an indictor of a plant's likelihood for survival in a given area, many factors, including soil type and fertility, soil moisture and drainage, humidity, and exposure to sun and wind determine a plant's growth and success or failure in its environment.
Areas above an arbitrary elevation are traditionally considered unsuitable for plant cropping and do not bear appropriate zone designations. There are also island zones that, because of elevation differences, are warmer or cooler than the surrounding areas and are given a different zone designation.
Note that many large urban areas carry a warmer zone designation than the surrounding countryside. The map contains as much detail as possible, considering the vast amount of data on which it is based and its size.
Sources:
- American Horticultural Society Heat Zone Map.
- Monrovia Gardening Information Center.
- USDA Miscellaneous Publication No. 1475. Issued January 1990. Authored by Henry M. Cathey while Director, U.S. National Arboretum. Edited, formatted and prepared for the US National Arboretum web site by Ramon Jordan, March 1998 & Revised March 2001.
Last Revised: October 31, 2007
Last Revised: Tuesday, January 6, 2009