History of Zone Maps
First developed in the United States in the 1920s and 1930s, the USDA (United States Department of Agriculture) hardiness zone map was not printed until the 1960s, later revised in 1965. The original Plant Hardiness Zone Map included 10 zones (10 being the warmest), based on gradients of 10 degrees Fahrenheit. Five years after the initial printing of the hardiness zone map, it was revised to include temperature data.
In 1990, the USDA revised the zone map, to include a new zone (Zone 11), which includes Mexico, California, parts of Florida and Hawaii. These areas have a minimum annual average temperature rate of 40 degrees Fahrenheit. Also changed, the temperature gradients from 10 to five degrees Fahrenheit. This was based on data of recorded temperatures between the years 1974 and 1986 and facts that these temperatures indicated a wider change in zones.
Both, new and seasoned gardeners understand the importance of plant hardiness zone maps. Gardeners consult their planting guides, to determine which plants are adaptable to their particular hardiness zone.
The different zones and the lowest temperatures for each one are as follows:
First developed in the United States in the 1920s and 1930s, the USDA (United States Department of Agriculture) hardiness zone map was not printed until the 1960s, later revised in 1965. The original Plant Hardiness Zone Map included 10 zones (10 being the warmest), based on gradients of 10 degrees Fahrenheit. Five years after the initial printing of the hardiness zone map, it was revised to include temperature data.
In 1990, the USDA revised the zone map, to include a new zone (Zone 11), which includes Mexico, California, parts of Florida and Hawaii. These areas have a minimum annual average temperature rate of 40 degrees Fahrenheit. Also changed, the temperature gradients from 10 to five degrees Fahrenheit. This was based on data of recorded temperatures between the years 1974 and 1986 and facts that these temperatures indicated a wider change in zones.
Both, new and seasoned gardeners understand the importance of plant hardiness zone maps. Gardeners consult their planting guides, to determine which plants are adaptable to their particular hardiness zone.
The different zones and the lowest temperatures for each one are as follows:
|
Zone 1: below -46 C
Zone 2: -46 to -40 C Zone 3: -40 to -34 C Zone 4: -34 to -29 C Zone 5: -29 to -23 C Zone 6: -23 to -18 C Zone 7: -18 to -12 C Zone 8: -12 to -7 C Zone 9: -7 to -1 C Zone 10: -1 to 4 C Zone 11: above 4 C |
(below -50 F)
(-50 to -40 F) (-40 to -30 F) (-30 to -20 F) (-20 to -10 F) (-10 to 0 F) (0 to 10 F) (10 to 20 F) |
How to Use
To find your residential zone, insert zip code.
