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Plant Hardiness And Heat Zones
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USDA Plant Hardiness Zone Map
 
The Plant Hardiness Zone Map tells you how cold your winters are, on average. It divides the US into 11 zones indicated by different colors. Each zone is 10°F warmer (or colder) in an average winter than the adjacent zone. The zone map is used to determine what plants are appropriate for specific locations. Most plant catalogs list the hardiness zone(s) that are best for each plant. You can use that information to help determine the best plants to grow in your particular location that can survive the winters, especially permanent landscape plants. This can also be used in conjunction with the The Heat Zone Map (see section below).

Note that USDA maps now split, and color code, zones 2 through10 (zone 11 represents frost-free areas) into 5°F sub-zones: "a" for the colder section [lighter color], "b" for the warmer section [darker color].

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.  Many large urban areas carry a warmer zone designation than the surrounding countryside.

USDA Hardiness Zone Map - National Arboretum

USDA Hardiness Zone Maps - Growit.com

USDA Hardiness Zone Map - NJ - Growit.com

USDA Hardiness Zone Finder - National Gardening Association and find plants by zone.

What Are Hardiness Zones? - National Arbor Day Foundation

USDA Plant Hardiness Zone Map - one page showing 11 zones without sub-divisions (Texas A&M):
http://aggie-horticulture.tamu.edu/wildseed/info/6.1.html


Canadian Hardiness Zone Map
 

 

Heat Zone Map
 
The American Horticultural Society's (AHS) Plant Heat Zone Map divides the US into 12 zones. The zones of the map indicate the average number of days each year that a given region experiences "heat days"-temperatures over 86 degrees (30 degrees Celsius). That is the point at which plants begin suffering physiological damage from heat. The zones range from Zone 1 (less than one heat day) to Zone 12 (more than 210 heat days). Many plant catalogs are now including this coding for heat tolerance. This is best used in conjunction with the Hardiness Zone Map (see section above).

 

AHS Heat Zone Map - Explanation, How To Use and Heat Zone Finder  (map is also downloadable in PDF format)

General

Click here for: A Gardener's Guide To Zone Maps - this gives a good overview of Zone Maps.  (Note: Article was produced by the National Gardening Association (NGA), and talks about their Zone Map, but currently it is using the USDA Hardiness Zone Map.)    [Alternate Link]   
See also: New Maps Reflect Heat Tolerance, Revised Zone Maps Help You Pick Ideal Plants and Selecting Plants: Will That Plant Grow Here? The Reality Of Zone Maps.

Sunset's Climate Zones -- Find Yours - this zone map takes into consideration: length of growing season, timing and amount of rainfall, winter lows, summer highs, humidity.  While national in coverage, its primary users are located West of the Rockies.  See also: Sunset Climate Zones 1-15 for details about each zone.

Climate Zones - at DoItYourself.com, find information on climate zones along with a variety of most recent maps.

Plant and Encyclopedia - find plant information including search by hardiness zone, provided by LandscapeUSA.com.

Tree I.D. Fact Sheets - find information on over 800 trees including search by hardiness zone, provided by Virginia Tech.

Weekend Gardener GrowGuide

USDA - PLANTS National Database (Realty Reality blog article)

Click here for index to additional blog articles regarding plants, gardening, landscaping and more.