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Arborday.org and USDA Plant Hardiness Zones
 

Enter your zip code in the form below, and we'll tell you where you fall in the Arborday.org Hardiness zones database.


What are Hardiness Zones?

Hardiness Zone Map

The Plant Hardiness Zones divide the United States and Canada into 11 areas based on a 10 degree Fahrenheit difference in the average annual minimum temperature. (The United States falls within Zones 2 through 10). For example, the lowest average temperature in Zone 2 is -50 to -40 degrees Fahrenheit, while the minimum average temperature in zone 10 is +30 to +40 degrees Fahrenheit.

Suggested hardiness zones have been indicated for all trees and perennials available online from the Foundation. If a range of zones, for example, zones 4-9, is indicated, the tree or perennial is known to be hardy in zones 4, 5, 6, 7, 8, and 9. Suitable hardiness means a plant can be expected to grow in the zone's temperature extremes, as determined by the lowest average annual temperature.

Keep in mind that local variations such as moisture, soil, winds, and other conditions might affect the viability of individual plants.

You may want to ask a Martha's Bloomers about which trees to plant in your community.


US National Arboretum

The 2003 US National Arboretum "Web Version" of the USDA Plant Hardiness Zone Map
USDA Miscellaneous Publication No. 1475, Issued January 1990

  • Introduction
  • How to use the new map
  • Additional Helpful Information
  • Hardiness Zone Details
  • Indicator Plant Examples
  • Introduction
    This map supersedes U.S. Department of Agriculture Miscellaneous Publication 814, "Plant Hardiness Zone Map," which was revised in 1965.  This 1990 version shows in detail the lowest temperatures that can be expected each year in the United States, Canada, and Mexico.  These temperatures are referred to as "average annual minimum temperatures" and are based on the lowest temperatures recorded for each of the years 1974 to 1986 in the United States and Canada and 1971 to 1984 in Mexico.  The map shows 10 different zones, each of which represents an area of winter hardiness for the plants of agriculture and our natural landscape.  It also introduces zone 11 to represent areas that have average annual minimum temperatures above 40 F (4.4 C) and that are therefore essentially frost free.

    How to Use the New Map
    Zones 2-10 in the map have been subdivided into light- and dark-colored sections (a and b) that represent 5 F (2.8 C) differences within the 10 F (5.6 C) zone.  The light color of each zone represents the colder section; the dark color, the warmer section.  Zone 11 represents any area where the average annual minimum temperature is above 40 F (4.4 C). The map shows 20 latitude and longitude lines.  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.

    In using the map to select a suitable environment for a landscape plant, today's gardeners should keep in mind the following:

      Stress Factors.  We became aware of additional stresses to plants during the 1970's.  Acid rain, gaseous and particulate pollution, security lighting, and toxic wastes, among many other stress factors, have significantly increased the potential for unsatisfactory performance of landscape plants.  We need to document the tolerances of plants to these factors.

      New Plant Management Systems.   New techniques of planting, transplanting, watering, fertilizing, and providing pest control measures have done much to increase the vigor of landscape plants.  But used unwisely, these same measures can reduce plant hardiness.

      Artificial Environments.    We have pushed the use of plants into totally artificial environments such as expressways, malls, elevated decks, and buildings where plant roots are totally removed from the ground and its warming influence.  The assortment of plants that can adapt to such environments is proving to be very restricted.  Hardiness ratings alone are inadequate to guide landscapers in selecting the most successful plants.


    Additional Helpful Information --
    Basic Plant Requirements  ||  How the Map Was Started
    How the Map Was Created  ||  Why the New Map was Created

    Hardiness Zones  --  Details

    Indicator Plant Examples --

      Listed by zone - Names of representative plants listed under the coldest zones in which they normally succeed.
      Listed alphabetically - Cold hardiness ratings (zones) for selected woody plants.

    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
    U.S. National Arboretum, Agricultural Research Service, U.S. Department of Agriculture, Washington, DC 20002

    Note:  This publication is not copyrighted, and permission to reproduce all or any part of it is not required.

     
     
           
       
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