Changes

[[Image:Zonescale.png|right|120px|thumb|Temperature scale of hardiness zones, showing the average annual minimum temperature boundaries for the zones]]

[[Image:Zonescale.png|right|120px|thumb|Temperature scale of hardiness zones, showing the average annual minimum temperature boundaries for the zones]]

A '''hardiness zone''' is a geographically-defined zone in which a specific category of [[plant]] life is capable of growing, as defined by [[temperature]] hardiness, or ability to withstand the minimum temperatures of the zone. The zones were first developed by the [[United States Department of Agriculture]] (USDA), and have subsequently been adopted elsewhere. They are categorized according to the mean of the lowest temperature recorded each winter, termed the "average annual minimum temperature". Thus if five successive winters reach respective minima of −14 °C, −12 °C, −8 °C, −16 °C, and −13 °C, the mean coldest temperature is −12.6 °C, placing the site in zone 7.

A '''hardiness zone''' is a geographically-defined zone in which a specific category of [[plant]] life is capable of growing, as defined by [[temperature]] hardiness, or ability to withstand the minimum temperatures of the zone. The zones were first developed by the [[United States Department of Agriculture]] (USDA), and have subsequently been adopted elsewhere. They are categorized according to the mean of the lowest temperature recorded each winter, termed the "average annual minimum temperature". Thus if five successive winters reach respective minima of −14 °C, −12 °C, −8 °C, −16 °C, and −13 °C, the mean coldest temperature is −12.6 °C, placing the site in zone 7.

==Benefits and criticisms==

==Benefits and criticisms==

An alternative system for describing plant hardiness is to use indicator plants (the USDA also publishes a list of these to go with their map). Common plants with known limits to their range are used. For example, many people will know whether lemons will grow in their locality. If you then say Geraldton Wax will grow more or less where lemons will grow you have defined the range of Geraldton Wax with some accuracy (whether or not it will flower is another problem). Unfortunately no two plant species have exactly the same requirements and there are even within-species differences. 'Meyer' lemons, for example, are more cold tolerant than 'Eureka'. You can really only define core areas and they are often fairly arbitrary.

An alternative system for describing plant hardiness is to use indicator plants (the USDA also publishes a list of these to go with their map). Common plants with known limits to their range are used. For example, many people will know whether lemons will grow in their locality. If you then say Geraldton Wax will grow more or less where lemons will grow you have defined the range of Geraldton Wax with some accuracy (whether or not it will flower is another problem). Unfortunately no two plant species have exactly the same requirements and there are even within-species differences. 'Meyer' lemons, for example, are more cold tolerant than 'Eureka'. You can really only define core areas and they are often fairly arbitrary.

==United Kingdom and Ireland Hardiness Zones==

 

===United Kingdom and Ireland Hardiness Zones===

[[Image:UK zonemap.png|thumb|UK hardiness zones]]

[[Image:UK zonemap.png|thumb|UK hardiness zones]]

Due to the moderating effect of the [[Gulf Stream]] on the [[Ireland|Irish]] and [[United Kingdom|UK]]'s [[temperate]] [[maritime climate]], the UK, and Ireland even more so, have rather milder winters than their northerly position suggests.

Due to the moderating effect of the [[Gulf Stream]] on the [[Ireland|Irish]] and [[United Kingdom|UK]]'s [[temperate]] [[maritime climate]], the UK, and Ireland even more so, have rather milder winters than their northerly position suggests.

The USDA first issued its standardized hardiness-zone map in 1960, and revised it in 1965. A new map was issued in 1990, based on U.S. and Canadian data from 1974 through 1986 (and 1971-1984 for Mexico). While the 1990-issue map utilized approximately double the number of stations, it also divided the temperature-zones into five-degree a/b zones for greater accuracy. This revised map showed many areas to be suddenly colder than the 1960 map, due largely to a number of severely colder winters in the central and eastern U.S. in the 1974-1986 data-gathering period as opposed to the mid-20th-century data-sampling period used in the 1960 map.

The USDA first issued its standardized hardiness-zone map in 1960, and revised it in 1965. A new map was issued in 1990, based on U.S. and Canadian data from 1974 through 1986 (and 1971-1984 for Mexico). While the 1990-issue map utilized approximately double the number of stations, it also divided the temperature-zones into five-degree a/b zones for greater accuracy. This revised map showed many areas to be suddenly colder than the 1960 map, due largely to a number of severely colder winters in the central and eastern U.S. in the 1974-1986 data-gathering period as opposed to the mid-20th-century data-sampling period used in the 1960 map.

The 1990 map shows 10 different zones, each of which represents an area of winter hardiness for the plants of agriculture and our natural landscape. This was revised to introduce zone 11, representing areas that have average annual minimum temperatures above 40°F (4.4°C) and that are therefore essentially frost-free.

The 1990 map shows 10 different zones, each of which represents an area of winter hardiness for the plants of agriculture and our natural landscape. This was revised to introduce zone 11, representing areas that have average annual minimum temperatures above 4°C and that are therefore essentially frost-free.

 

===Updates===

===Updates===

Once the Foundation analyzed the new data, hardiness zones were revised, generally reflecting warmer recent temperatures in many parts of the country. The Arbor Day Foundation used the updated versions of the same sources of data as had been utilized by the U.S. Department of Agriculture in the creation of its hardiness zone maps.  The 2004 map appears to validate the data used in the 2003 draft completed by the AHS. Like the AHS map, it also did away with the more detailed a/b half-zone delineations. http://www.arborday.org/media/zones.cfm

Once the Foundation analyzed the new data, hardiness zones were revised, generally reflecting warmer recent temperatures in many parts of the country. The Arbor Day Foundation used the updated versions of the same sources of data as had been utilized by the U.S. Department of Agriculture in the creation of its hardiness zone maps.  The 2004 map appears to validate the data used in the 2003 draft completed by the AHS. Like the AHS map, it also did away with the more detailed a/b half-zone delineations. http://www.arborday.org/media/zones.cfm

===U.S. Cities===

==Sunset Hardiness Zones==

[[Image:BGClimate430.jpg|thumb|250px|right|Sunset Map of US/Canada hardiness zones.  An interactive version of this map is available at http://www.sunset.com/sunset/garden/article/1,20633,845218,00.html]]  

A plant's performance is governed by the total climate: length of growing season, timing and amount of rainfall, winter lows, summer highs, humidity. Sunset's climate zone maps take all these factors into account — unlike the familiar hardiness zone maps devised by the U.S. Department of Agriculture, which divide the U.S. and Canada into zones based strictly on winter lows. The U.S.D.A. maps tell you only where a plant may survive the winter; Sunset climate zone maps let you see where that plant will thrive year-round.

| [[Albuquerque, New Mexico]] || '''7''' || [[Oklahoma City, Oklahoma]] || '''7'''

| [[Anchorage, Alaska]] || '''4''' || [[Omaha, Nebraska]] || '''5'''

| [[Atlanta, Georgia]] || '''7-8''' || [[Orlando, Florida]] || '''9-10'''

| [[Baltimore, Maryland]] || '''7-8''' || [[Philadelphia, Pennsylvania]] || '''7'''

| [[Boston, Massachusetts]] || '''6-7''' || [[Phoenix, Arizona]] || '''9'''

| [[Denver, Colorado]] || '''5-6'''|| [[St. Louis, Missouri]] || '''6'''

| [[Nashville, Tennessee]] || '''7'''|| [[Washington, D.C.]] || '''7-8'''

==Australian Hardiness Zones==

==Australian Hardiness Zones==

There are problems with this classifications of this type: the spread of weather stations is insufficient to give clear zones and too many places with different climates are lumped together. Only 738 Australian stations have records of more than ten years (one station per 98,491 hectares), though more populated areas have relatively fewer hectares per station. Local factors such as aspect, altitude, proximity to the sea also complicate the matter. For example, Mt. Isa has three climatic stations with more than a ten year record. One is in Zone 4a, one in Zone 4b and the other is in Zone 5a. Likewise, Sydney residents can choose between Zones 3a and 4b. Most other cities have similar problems. Different locations in the same city are suitable for different plants, making it hard to draw a meaningful map. There may even be a case for publishing a list of weather stations and their zone classification to allow best use of local conditions.

There are problems with this classifications of this type: the spread of weather stations is insufficient to give clear zones and too many places with different climates are lumped together. Only 738 Australian stations have records of more than ten years (one station per 98,491 hectares), though more populated areas have relatively fewer hectares per station. Local factors such as aspect, altitude, proximity to the sea also complicate the matter. For example, Mt. Isa has three climatic stations with more than a ten year record. One is in Zone 4a, one in Zone 4b and the other is in Zone 5a. Likewise, Sydney residents can choose between Zones 3a and 4b. Most other cities have similar problems. Different locations in the same city are suitable for different plants, making it hard to draw a meaningful map. There may even be a case for publishing a list of weather stations and their zone classification to allow best use of local conditions.

==See also==

==See also==