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A hardiness zone is a geographic area defined as having a certain average annual minimum temperature, a factor relevant to the survival of many plants. In some systems other statistics are included in the calculations. The original and most widely used system, developed by the
United States Department of Agriculture The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...
(USDA) as a rough guide for landscaping and gardening, defines 13 zones by long-term average annual extreme minimum temperatures. It has been adapted by and to other countries (such as Canada) in various forms. Unless otherwise specified, in American contexts "hardiness zone" or simply "zone" usually refers to the USDA scale. For example, a plant may be described as "hardy to zone 10": this means that the plant can withstand a minimum temperature of 30 °F (−1.1 °C) to 40 °F (4.4 °C). Other hardiness rating schemes have been developed as well, such as the UK
Royal Horticultural Society The Royal Horticultural Society (RHS), founded in 1804 as the Horticultural Society of London, is the UK's leading gardening charity. The RHS promotes horticulture through its five gardens at Wisley (Surrey), Hyde Hall (Essex), Harlow Carr (Nor ...
and US Sunset Western Garden Book systems. A heat zone (see below) is instead defined by annual high temperatures; the
American Horticultural Society The American Horticultural Society (AHS) is a nonprofit, membership-based organization that promotes excellence in American horticulture. It is headquartered at River Farm in Alexandria, Virginia. History Established in 1922, the AHS is one of ...
(AHS) heat zones use the average number of days per year when the temperature exceeds .


United States hardiness zones (USDA scale)

The USDA system was originally developed to aid gardeners and landscapers in the United States. State-by-state maps, along with an electronic system that allows finding the zone for a particular zip code, can be found at the USDA Agricultural Research Service (USDA-ARS) website. In the United States, most of the warmer zones (zones 9, 10, and 11) are located in the deep southern half of the country and on the southern coastal margins. Higher zones can be found in
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
(up to 12) and
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
(up to 13). The southern middle portion of the mainland and central coastal areas are in the middle zones (zones 8, 7, and 6). The far northern portion on the central interior of the mainland have some of the coldest zones (zones 5, 4, and small area of zone 3) and often have much less consistent range of temperatures in winter due to being more continental, especially further west with higher diurnal temperature variations, and thus the zone map has its limitations in these areas. Lower zones can be found in
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...
(down to 1). The low latitude and often stable weather in
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
, the Gulf Coast, and southern
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
and
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
, are responsible for the rarity of episodes of severe cold relative to normal in those areas. The warmest zone in the
48 contiguous states The contiguous United States (officially the conterminous United States) consists of the 48 adjoining U.S. states and the Federal District of the United States of America. The term excludes the only two non-contiguous states, Alaska and Hawaii ...
is the
Florida Keys The Florida Keys are a coral cay archipelago located off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami, and e ...
(11b) and the coldest is in north-central
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over t ...
(2b). A couple of locations on the northern coast of Puerto Rico have the warmest hardiness zone in the United States at 13b. Conversely, isolated inland areas of Alaska have the coldest hardiness zone in the United States at 1a.


Definitions


History

The first attempts to create a geographical hardiness zone system were undertaken by two researchers at the
Arnold Arboretum The Arnold Arboretum of Harvard University is a botanical research institution and free public park, located in the Jamaica Plain and Roslindale neighborhoods of Boston, Massachusetts. Established in 1872, it is the oldest public arboretum in ...
in
Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...
: the first was published in 1927 by
Alfred Rehder Alfred Rehder (4 September 1863 in Waldenburg, Saxony – 25 July 1949 in Jamaica Plain, Massachusetts) was a German-American botanical taxonomist and dendrologist who worked at the Arnold Arboretum of Harvard University. He is generally ...
, and the second by
Donald Wyman Donald Wyman (1904 — 6 December 1993) was an American horticulturist, the head of horticulture at Harvard University's Arnold Arboretum from 1935 to 1970. He took a bachelor's degree in horticulture from Pennsylvania State College (1926) and a ma ...
in 1938. The Arnold map was subsequently updated in 1951, 1967, and finally 1971, but eventually fell out of use completely. The modern USDA system began at the US National Arboretum in
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...
. The first map was issued in 1960, and revised in 1965. It used uniform 10-degree Fahrenheit ranges, and gradually became widespread among American gardeners. The USDA map was revised and reissued in 1990 with freshly available climate data, this time with 5-degree distinctions dividing each zone into new "a" and "b" subdivisions. In 2003, the
American Horticultural Society The American Horticultural Society (AHS) is a nonprofit, membership-based organization that promotes excellence in American horticulture. It is headquartered at River Farm in Alexandria, Virginia. History Established in 1922, the AHS is one of ...
(AHS) produced a draft revised map, using temperature data collected from July 1986 to March 2002. The 2003 map placed many areas approximately a half-zone higher (warmer) than the USDA's 1990 map. Reviewers noted the map zones appeared to be closer to the original USDA 1960 map in its overall zone delineations. Their map purported to show finer detail, for example, reflecting
urban heat island An urban heat island (UHI) is an urban or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent ...
s by showing the downtown areas of several cities (e.g.,
Baltimore, Maryland Baltimore ( , locally: or ) is the most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic, and the 30th most populous city in the United States with a population of 585,708 in 2020. Baltimore wa ...
; Washington, D.C. and
Atlantic City, New Jersey Atlantic City, often known by its initials A.C., is a coastal resort city in Atlantic County, New Jersey, United States. The city is known for its casinos, boardwalk, and beaches. In 2020, the city had a population of 38,497.
) as a full zone warmer than outlying areas. The map excluded the detailed a/b half-zones introduced in the USDA's 1990 map, an omission widely criticized by horticulturists and gardeners due to the coarseness of the resulting map. The USDA rejected the AHS 2003 draft map and created its own map in an interactive computer format, which the American Horticultural Society now uses. In 2006, the Arbor Day Foundation released an update of U.S. hardiness zones, using mostly the same data as the AHS. It revised hardiness zones, reflecting generally warmer recent temperatures in many parts of the country, and appeared similar to the AHS 2003 draft. The Foundation also did away with the more detailed a/b half-zone delineations. In 2012 the USDA updated their plant hardiness map based on 1976–2005 weather data, using a longer period of data to smooth out year-to-year weather fluctuations. Two new zones (12 and 13) were added to better define and improve information sharing on tropical and semitropical plants, they also appear on the maps of Hawaii and Puerto Rico. There is a very small spot east of
San Juan San Juan, Spanish for Saint John, may refer to: Places Argentina * San Juan Province, Argentina * San Juan, Argentina, the capital of that province * San Juan, Salta, a village in Iruya, Salta Province * San Juan (Buenos Aires Underground), ...
, Puerto Rico that includes the airport in coastal Carolina, where the mean minimum is 67 degrees F (19 C), which is classified as hardiness Zone 13b, the highest category, with temperatures rarely below . The map has a higher resolution than previous ones, and is able to show local variations due to things such as elevation or large bodies of water. Many zone boundaries were changed as a result of the more recent data, as well as new mapping methods and additional information gathered. Many areas were a half zone warmer than the previous 1990 map. The 2012 map was created digitally for the internet, and includes a ZIP Code zone finder and an interactive map. In 2015, the Arbor Day Foundation revised another map, also with no a and b subdivisions, showing many areas having zones even warmer, with the most notable changes in the Mid Atlantic and Northeast, showing cities like Philadelphia, New York City and Washington D.C in zone 8, due to their urban heat islands.


Selected U.S. cities

The USDA plant hardiness zones for selected U.S. cities as based on the 2012 map are the following:


Limitations

As the USDA system is based entirely on average annual extreme minimum temperature in an area, it is limited in its ability to describe the climatic conditions a gardener may have to account for in a particular area: there are many other factors that determine whether or not a given plant can survive in a given zone. Zone information alone is often not adequate for predicting winter survival, since factors such as frost dates and frequency of snow cover can vary widely between regions. Even the extreme minimum itself may not be useful when comparing regions in widely different climate zones. As an extreme example, due to the
Gulf stream The Gulf Stream, together with its northern extension the North Atlantic Drift, is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida and up the eastern coastline of the Unit ...
most of the United Kingdom is in zones 8–9, while in the US, zones 8–9 include regions such as the subtropical coastal areas of the southeastern US and Mojave and Chihuahuan inland deserts, thus an American gardener in such an area may only have to plan for several nights of cold temperatures per year, while their British counterpart may have to plan for several months. In addition, the zones do not incorporate any information about duration of cold temperatures, summer temperatures, or sun intensity
insolation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...
; thus sites which may have the same mean winter minima on the few coldest nights and be in the same garden zone, but have markedly different climates. For example, zone 8 covers coastal, high latitude, cool summer locations like
Seattle Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest region o ...
and
London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
, as well as lower latitude, subtropical hot summer climates like Charleston and
Madrid Madrid ( , ) is the capital and most populous city of Spain. The city has almost 3.4 million inhabitants and a metropolitan area population of approximately 6.7 million. It is the second-largest city in the European Union (EU), and ...
. Farmers, gardeners, and landscapers in the former two must plan for entirely different growing conditions from those in the latter, in terms of length of hot weather and sun intensity. Coastal Ireland and central Florida are both Zone 10, but have radically different climates 99% of the year. The hardiness scales do not take into account the reliability of snow cover in the colder zones. Snow acts as an insulator against extreme cold, protecting the root system of hibernating plants. If the snow cover is reliable, the actual temperature to which the roots are exposed will not be as low as the hardiness zone number would indicate. As an example,
Quebec City Quebec City ( or ; french: Ville de Québec), officially Québec (), is the capital city of the Canadian province of Quebec. As of July 2021, the city had a population of 549,459, and the metropolitan area had a population of 839,311. It is t ...
in Canada is located in zone 4, but can rely on a significant snow cover every year, making it possible to cultivate plants normally rated for zones 5 or 6. But, in
Montreal Montreal ( ; officially Montréal, ) is the second-most populous city in Canada and most populous city in the Canadian province of Quebec. Founded in 1642 as '' Ville-Marie'', or "City of Mary", it is named after Mount Royal, the triple- ...
, located to the southwest in zone 5, it is sometimes difficult to cultivate plants adapted to the zone because of the unreliable snow cover. Many plants may survive in a locality but will not flower if the day length is insufficient or if they require
vernalization Vernalization (from Latin ''vernus'', "of the spring") is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower ...
(a particular duration of low temperature). There are many other climate parameters that a farmer, gardener, or landscaper may need to take into account as well, such as humidity, precipitation, storms, rainy-dry cycles or monsoons, and site considerations such as soil type, soil drainage and water retention, water table, tilt towards or away from the sun, natural or manmade protection from excessive sun, snow, frost, and wind, etc. The annual extreme minimum temperature is a useful indicator, but ultimately only one factor among many for plant growth and survival.


Alternatives

An alternative means of describing plant hardiness is to use "indicator plants". In this method, common plants with known limits to their range are used. ''
Sunset Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth (except the North and South poles), the equinox Sun sets due west at the moment of both the spr ...
'' publishes a series that breaks up climate zones more finely than the USDA zones, identifying 45 distinct zones in the US, incorporating ranges of temperatures in all seasons, precipitation, wind patterns, elevation, and length and structure of the growing season.''Sunset National Garden Book''. Sunset Books Inc. Menlo Park, California (1997) In addition, the Köppen climate classification system can be used as a more general guide to growing conditions when considering large areas of the Earth's surface or attempting to make comparisons between different continents. The Trewartha climate classification is often a good "real world" concept of climates and their relation to plants and their average growing conditions.


Australian hardiness zones

The
Australian National Botanic Gardens The Australian National Botanic Gardens (ANBG) is a heritage-listed botanical garden located in , Canberra, in the Australian Capital Territory, Australia. Established in 1949, the Gardens is administered by the Australian Government's Departm ...
have devised another system keeping with Australian conditions. The zones are defined by steps of 5 degrees Celsius, from −15–−10 °C for zone 1 to 15–20 °C for zone 7. They are numerically about 6 lower than the USDA system. For example, Australian zone 3 is roughly equivalent to USDA zone 9. The higher Australian zone numbers had no US equivalents prior to the 2012 addition by USDA of zones 12 and 13. The spread of weather stations may be insufficient and too many places with different climates are lumped together. Only 738 Australian stations have records of more than ten years (one station per ), though more populated areas have relatively fewer hectares per station. Mount 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. Sydney residents are split between zones 3a and 4b. Different locations in the same city are suitable for different plants.


Canadian hardiness zones

Climate variables that reflect the capacity and detriments to plant growth are used to develop an index that is mapped to Canada's Plant Hardiness Zones. This index comes from a formula originally developed by Ouellet and Sherk in the mid-1960s. The formula used is: where: * Y = estimated index of suitability * X1 = monthly mean of the daily minimum temperatures (°C) of the coldest month * X2 = mean frost free period above 0 °C in days * X3 = amount of rainfall (R) from June to November, inclusive, in terms of R/(R+a) where a=25.4 if R is in millimeters and a=1 if R is in inches * X4 = monthly mean of the daily maximum temperatures (°C) of the warmest month * X5 = winter factor expressed in terms of (0 °C – X1)Rjan where Rjan represents the rainfall in January expressed in mm * X6 = mean maximum snow depth in terms of S/(S+a) where a=25.4 if S is in millimeters and a=1 if S is in inches * X7 = maximum wind gust in (km/hr) in 30 years. For practical purposes, Canada has adopted the American hardiness zone classification system. The 1990 version of the USDA Plant Hardiness Zone Map included Canada and Mexico, but they were removed with the 2012 update to focus on the United States and Puerto Rico. The Canadian government publishes both Canadian and USDA-style zone maps.


European hardiness zones


Selected European cities

The table below provides USDA hardiness zone data for selected European cities:


Britain and Ireland

USDA zones do not work particularly well in the UK as they are designed for continental climates and subtropical climates. The high latitude, weaker solar intensity, and cooler UK summers must be considered when comparing to US equivalent. New growth may be insufficient or fail to harden off affecting winter survival in the shorter and much cooler UK summers. Owing to the moderating effect of the North Atlantic Current on the Irish and British
temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...
maritime climate, Britain, and Ireland even more so, have milder winters than their northerly position would otherwise afford. This means that the USDA hardiness zones relevant to Britain and Ireland are quite high, from 7 to 10, as shown below. In 2012 the United Kingdom's Royal Horticultural Society introduced new hardiness ratings for plants, not places. These run from H7, the hardiest (tolerant of temperatures below ) to H1a (needing temperatures above ). The RHS hardiness ratings are based on absolute minimum winter temperatures (in °C) rather than the long-term average annual extreme minimum temperatures that define USDA zones.


Scandinavia and Baltic Sea Region

Scandinavia lies at the same latitude as Alaska or Greenland, but the effect of the warm North Atlantic Current is even more pronounced here than it is in Britain and Ireland. Save for a very small spot near Karasjok, Norway, which is in zone 2, nowhere in the Arctic part of Scandinavia gets below zone 3. The
Faroe Islands The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic island group and an autonomous territory of the Kingdom of Denmark. They are located north-northwest of Scotland, and about halfway bet ...
, at 62–63°N are in zone 8, as are the outer
Lofoten Islands Lofoten () is an archipelago and a traditional district in the county of Nordland, Norway. Lofoten has distinctive scenery with dramatic mountains and peaks, open sea and sheltered bays, beaches and untouched lands. There are two towns, Svolv� ...
at 68°N.
Tromsø Tromsø (, , ; se, Romsa ; fkv, Tromssa; sv, Tromsö) is a municipality in Troms og Finnmark county, Norway. The administrative centre of the municipality is the city of Tromsø. Tromsø lies in Northern Norway. The municipality is the ...
(, a coastal city in Norway at 70°N, is in zone 7, and even
Longyearbyen Longyearbyen (, locally �lɔ̀ŋjɑrˌbyːən "The Longyear Town") is the world's northernmost settlement with a population greater than 1,000 and the largest inhabited area of Svalbard, Norway. It stretches along the foot of the left bank ...
, the northernmost true city in the world at 78°N, is still in zone 4. All these coastal locations have one thing in common, though, which are cool, damp summers, with temperatures rarely exceeding (or in Longyearbyen). This shows the importance of taking heat zones into account for better understanding of what may or may not grow. In Sweden and Finland generally, at sea level to , zone 3 is north of the Arctic Circle, including cities like Karesuando and
Pajala Pajala () is a locality and the seat of Pajala Municipality in Norrbotten County, Sweden, with 1,958 inhabitants in 2010. It is located in Swedish Lapland. Pajala is in the Torne Valley and was dominated by people speaking a Finnish dialect unt ...
.
Kiruna (; se, Giron ; fi, Kiiruna ) is the northernmost city in Sweden, situated in the province of Lapland. It had 17,002 inhabitants in 2016 and is the seat of Kiruna Municipality (population: 23,167 in 2016) in Norrbotten County. The city was ...
is the major exception here, which being located on a hill above frost traps, is in zone 5. Zone 4 lies between the Arctic Circle and about 64–66°N, with cities such as
Oulu Oulu ( , ; sv, Uleåborg ) is a city, municipality and a seaside resort of about 210,000 inhabitants in the region of North Ostrobothnia, Finland. It is the most populous city in northern Finland and the fifth most populous in the country after ...
,
Rovaniemi Rovaniemi ( , ; sme, Roavvenjárga ; smn, Ruávinjargâ; sms, Ruäʹvnjargg) is a city and municipality of Finland. It is the administrative capital and commercial centre of Finland's northernmost province, Lapland, and its southern part Pe ...
and Jokkmokk, zone 5 (south to 61–62°N) contains cities such as
Tampere Tampere ( , , ; sv, Tammerfors, ) is a city in the Pirkanmaa region, located in the western part of Finland. Tampere is the most populous inland city in the Nordic countries. It has a population of 244,029; the urban area has a population ...
,
Umeå Umeå ( , , , locally ; South Westrobothnian: ;). fi, Uumaja; sju, Ubmeje; sma, Upmeje; se, Ubmi) is a city in northeast Sweden. It is the seat of Umeå Municipality and the capital of Västerbotten County. Situated on the Ume River, Um ...
, and
Östersund Östersund (; sma, Staare) is an urban area (city) in Jämtland in the middle of Sweden. It is the seat of Östersund Municipality and the capital of Jämtland County. Östersund is located at the shores of Sweden's fifth-largest lake, Storsjön, ...
. Zone 6 covers the south of mainland Finland, Sweden north of 60°N, and the high plateau of
Småland Småland () is a historical province () in southern Sweden. Småland borders Blekinge, Scania, Halland, Västergötland, Östergötland and the island Öland in the Baltic Sea. The name Småland literally means ''Small Lands''. The Latinized f ...
further south. Here one will find cities such as
Gävle Gävle () is a city in Sweden, the seat of Gävle Municipality and the capital of Gävleborg County. It had 77,586 inhabitants in 2020, which makes it the 13th most populated city in Sweden. It is the oldest city in the historical Norrland (Swed ...
,
Örebro Örebro ( , ) is the sixth-largest city in Sweden, the seat of Örebro Municipality, and capital of the Örebro County. It is situated by the Närke Plain, near the lake Hjälmaren, a few kilometers inland along the small river Svartån, and ...
,
Sundsvall Sundsvall () is a city and the seat of Sundsvall Municipality in Västernorrland County, Sweden. It has a population of 58,807 as of 2020; more than 95,000 live in the municipal area. It is Sweden's 21st largest city by population. History The ...
, and
Helsinki Helsinki ( or ; ; sv, Helsingfors, ) is the Capital city, capital, primate city, primate, and List of cities and towns in Finland, most populous city of Finland. Located on the shore of the Gulf of Finland, it is the seat of the region of U ...
.
Åland Åland ( fi, Ahvenanmaa: ; ; ) is an autonomous and demilitarised region of Finland since 1920 by a decision of the League of Nations. It is the smallest region of Finland by area and population, with a size of 1,580 km2, and a populat ...
, as well as coastal southern Sweden, and the
Stockholm Stockholm () is the capital and largest city of Sweden as well as the largest urban area in Scandinavia. Approximately 980,000 people live in the municipality, with 1.6 million in the urban area, and 2.4 million in the metropo ...
area are in zone 7. The west coast of Sweden (
Gothenburg Gothenburg (; abbreviated Gbg; sv, Göteborg ) is the second-largest city in Sweden, fifth-largest in the Nordic countries, and capital of the Västra Götaland County. It is situated by the Kattegat, on the west coast of Sweden, and has ...
and southwards) enjoys particularly mild winters and lies in zone 7, therefore being friendly to some hardy exotic species (found, for example, in the Gothenburg Botanical Garden), the southeast coast of Sweden has a colder winter due to the absence of the Gulf Stream. Denmark is in zones 9a, 8b, and 8a. Estonia is divided to warmer West and North coast (
Tallinn Tallinn () is the most populous and capital city of Estonia. Situated on a bay in north Estonia, on the shore of the Gulf of Finland of the Baltic Sea, Tallinn has a population of 437,811 (as of 2022) and administratively lies in the Harju '' ...
6b, Haapsalu 7b, Kärdla 7a, Kuressaare 7a, Paide 6a, Rakvere 6a, Narva 6a, Viljandi 6b) and colder inland (Tartu 5a, Valga 5a, Võru 5a). Latvia's capital
Riga Riga (; lv, Rīga , liv, Rīgõ) is the capital and largest city of Latvia and is home to 605,802 inhabitants which is a third of Latvia's population. The city lies on the Gulf of Riga at the mouth of the Daugava river where it meets the ...
is in zone 6b. The country is in zones 5a, 5b, 6a, 6b, 7a and 7b. Lithuania's capital
Vilnius Vilnius ( , ; see also other names) is the capital and largest city of Lithuania, with a population of 592,389 (according to the state register) or 625,107 (according to the municipality of Vilnius). The population of Vilnius's functional urba ...
is in zone 5b. The country is in zones 5b, 6a, 6b and 7a.meteo.lt
Atšiaurumo zonos Lietuvoje
, Lietuvos hidrometeorologijos tarnyba , 2022-05-09


Central Europe

Central Europe is a good example of a transition from an
oceanic climate An oceanic climate, also known as a marine climate, is the humid temperate climate sub-type in Köppen classification ''Cfb'', typical of west coasts in higher middle latitudes of continents, generally featuring cool summers and mild winters ...
to a
continental climate Continental climates often have a significant annual variation in temperature (warm summers and cold winters). They tend to occur in the middle latitudes (40 to 55 north), within large landmasses where prevailing winds blow overland bringing so ...
, which reflects in the tendency of the hardiness zones to decrease mainly eastwards instead of northwards. Also, the plateaus and low mountain ranges in this region have a significant impact on how cold it might get during winter. Generally speaking, the hardiness zones are high considering the latitude of the region, although not as high as Northern Europe with the
Shetland Islands Shetland, also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in Scotland lying between Orkney, the Faroe Islands and Norway. It is the northernmost region of the United Kingdom. The islands lie about to the n ...
where zone 9 extends to over 60°N. In Central Europe, the relevant zones decrease from zone 8 on the Belgian, Dutch, and German
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian ...
coast, with the exception of some of the Frisian Islands (notably Vlieland and Terschelling), the island of Helgoland, and some of the islands in the
Rhine ), Surselva, Graubünden, Switzerland , source1_coordinates= , source1_elevation = , source2 = Rein Posteriur/Hinterrhein , source2_location = Paradies Glacier, Graubünden, Switzerland , source2_coordinates= , source ...
-
Scheldt The Scheldt (french: Escaut ; nl, Schelde ) is a river that flows through northern France, western Belgium, and the southwestern part of the Netherlands, with its mouth at the North Sea. Its name is derived from an adjective corresponding to ...
estuary, which are in zone 9, to zone 5 around Suwałki, Podlachia on the far eastern border between
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ...
and
Lithuania Lithuania (; lt, Lietuva ), officially the Republic of Lithuania ( lt, Lietuvos Respublika, links=no ), is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea. Lithuania ...
. Some isolated, high elevation areas of the
Alps The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...
and
Carpathians The Carpathian Mountains or Carpathians () are a range of mountains forming an arc across Central Europe. Roughly long, it is the third-longest European mountain range after the Urals at and the Scandinavian Mountains at . The range stretche ...
may even go down to zone 3 or 4. An extreme example of a cold sink is
Funtensee Funtensee is a karst lake on the Steinernes Meer plateau in Berchtesgaden National Park, Bavaria, Germany. It is located in the larger of two sinkholes (also referred to as uvala). The area is known for record low temperatures, up to 30 � ...
,
Bavaria Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total l ...
which is at least in zone 3. Another notable example is
Waksmund Waksmund is a village in the administrative district of Gmina Nowy Targ, within Nowy Targ County, Lesser Poland Voivodeship, in southern Poland. It lies approximately east of Nowy Targ and south of the regional capital Kraków. The village ...
, a small village in the Polish
Carpathians The Carpathian Mountains or Carpathians () are a range of mountains forming an arc across Central Europe. Roughly long, it is the third-longest European mountain range after the Urals at and the Scandinavian Mountains at . The range stretche ...
, which regularly reaches during winter on calm nights when cold and heavy airmasses from the surrounding Gorce and Tatra Mountains descend down the slopes to this low-lying valley, creating extremes which can be up to colder than nearby Nowy Targ or Białka Tatrzańska, which are both higher up in elevation. Waksmund is in zone 3b while nearby
Kraków Kraków (), or Cracow, is the second-largest and one of the oldest cities in Poland. Situated on the Vistula, Vistula River in Lesser Poland Voivodeship, the city dates back to the seventh century. Kraków was the official capital of Poland un ...
, only to the north and lower is in zone 6a. These examples prove that local topography can have a pronounced effect on temperature and thus on what is possible to grow in a specific region.


Southern Europe

The southern European marker plant for climate as well as cultural indicator is the olive tree, which cannot withstand long periods below freezing so its cultivation area matches the cool winter zone. The
Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
acts as a temperature regulator, so this area is generally warmer than other parts of the continent; except in mountainous areas where the sea effect lowers, it belongs in zones 8–10; however, southern Balkans (mountainous Western and Eastern
Serbia Serbia (, ; Serbian: , , ), officially the Republic of Serbia ( Serbian: , , ), is a landlocked country in Southeastern and Central Europe, situated at the crossroads of the Pannonian Basin and the Balkans. It shares land borders with Hu ...
, continental
Croatia , image_flag = Flag of Croatia.svg , image_coat = Coat of arms of Croatia.svg , anthem = " Lijepa naša domovino"("Our Beautiful Homeland") , image_map = , map_caption = , capi ...
, and
Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedo ...
) are colder in winter and are in zones 6–7. The Croatian (
Dalmatia Dalmatia (; hr, Dalmacija ; it, Dalmazia; see names in other languages) is one of the four historical regions of Croatia, alongside Croatia proper, Slavonia, and Istria. Dalmatia is a narrow belt of the east shore of the Adriatic Sea, str ...
n) coast,
Albania Albania ( ; sq, Shqipëri or ), or , also or . officially the Republic of Albania ( sq, Republika e Shqipërisë), is a country in Southeastern Europe. It is located on the Adriatic and Ionian Seas within the Mediterranean Sea and share ...
, and northern
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...
are in zones 8–9, as are central-northern
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
(hills and some spots in
Po Valley The Po Valley, Po Plain, Plain of the Po, or Padan Plain ( it, Pianura Padana , or ''Val Padana'') is a major geographical feature of Northern Italy. It extends approximately in an east-west direction, with an area of including its Venetic ex ...
are however colder) and southern
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
; Central
Iberia The Iberian Peninsula (), ** * Aragonese language, Aragonese and Occitan language, Occitan: ''Peninsula Iberica'' ** ** * french: Péninsule Ibérique * mwl, Península Eibérica * eu, Iberiar penintsula also known as Iberia, is a pe ...
is 8–9 (some highland areas are slightly colder). The Spanish and Portuguese Atlantic coast, much of
Andalusia Andalusia (, ; es, Andalucía ) is the southernmost autonomous community in Peninsular Spain. It is the most populous and the second-largest autonomous community in the country. It is officially recognised as a "historical nationality". The ...
and Murcia, coastal and slightly inland southern
Valencian Community The Valencian Community ( ca-valencia, Comunitat Valenciana, es, Comunidad Valenciana) is an autonomous community of Spain. It is the fourth most populous Spanish autonomous community after Andalusia, Catalonia and the Community of Madrid wi ...
, a part of coastal
Catalonia Catalonia (; ca, Catalunya ; Aranese Occitan: ''Catalonha'' ; es, Cataluña ) is an autonomous community of Spain, designated as a '' nationality'' by its Statute of Autonomy. Most of the territory (except the Val d'Aran) lies on the no ...
, the
Balearic Islands The Balearic Islands ( es, Islas Baleares ; or ca, Illes Balears ) are an archipelago in the Balearic Sea, near the eastern coast of the Iberian Peninsula. The archipelago is an autonomous community and a province of Spain; its capital is ...
, southwestern
Sardinia Sardinia ( ; it, Sardegna, label=Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label= Algherese and Catalan) is the second-largest island in the Mediterranean Sea, aft ...
, most of
Sicily (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...
, coastal southern Italy, some areas around
Albania Albania ( ; sq, Shqipëri or ), or , also or . officially the Republic of Albania ( sq, Republika e Shqipërisë), is a country in Southeastern Europe. It is located on the Adriatic and Ionian Seas within the Mediterranean Sea and share ...
, coastal Cyprus and southwestern Greece are in zone 10. In Europe, the zone 11a is limited only to a few spots. In the Iberian Peninsula, it can be found on the southern coast, namely in populated Spanish areas such as the cities of
Almería Almería (, , ) is a city and municipality of Spain, located in Andalusia. It is the capital of the province of the same name. It lies on southeastern Iberia on the Mediterranean Sea. Caliph Abd al-Rahman III founded the city in 955. The city g ...
, Adra, Nerja,
Málaga Málaga (, ) is a municipality of Spain, capital of the Province of Málaga, in the autonomous community of Andalusia. With a population of 578,460 in 2020, it is the second-most populous city in Andalusia after Seville and the sixth most po ...
, Marbella and in a strip of coastal land between Tarifa and Punta Carnero in the province of Cádiz. In
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of th ...
, zone 11a can be found in the Southwest on a few unpopulated sites around the municipalities of
Lagos Lagos (Nigerian English: ; ) is the largest city in Nigeria and the second most populous city in Africa, with a population of 15.4 million as of 2015 within the city proper. Lagos was the national capital of Nigeria until December 1991 fo ...
and Vila do Bispo. In
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...
, zone 11a can be found in areas of
Crete Crete ( el, Κρήτη, translit=, Modern: , Ancient: ) is the largest and most populous of the Greek islands, the 88th largest island in the world and the fifth largest island in the Mediterranean Sea, after Sicily, Sardinia, Cyprus, ...
,
Karpathos Karpathos ( el, Κάρπαθος, ), also Carpathos, is the second largest of the Greek Dodecanese islands, in the southeastern Aegean Sea. Together with the neighboring smaller Saria Island it forms the municipality of Karpathos, which is part of ...
and
Antiparos Antiparos ( ell, Αντίπαρος; grc, Ὠλίαρος, Oliaros; la, Oliarus; is a small island in the southern Aegean, at the heart of the Cyclades, which is less than one nautical mile (1.9 km) from Paros, the port to which it is conn ...
islands. The Mediterranean islands of
Malta Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of an archipelago, between Italy and Libya, and is often considered a part of Southern Europe. It lies ...
,
Lampedusa Lampedusa ( , , ; scn, Lampidusa ; grc, Λοπαδοῦσσα and Λοπαδοῦσα and Λοπαδυῦσσα, Lopadoûssa; mt, Lampeduża) is the largest island of the Italian Pelagie Islands in the Mediterranean Sea. The '' comune'' of ...
and Linosa belong to zone 11a as well as a few areas on the southernmost coast of
Cyprus Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is ...
. The Balkan area is also more prone to cold snaps and episodes of unseasonable warmth. For instance, despite having similar daily means and temperature amplitudes to
Nantucket, Massachusetts Nantucket () is an island about south from Cape Cod. Together with the small islands of Tuckernuck and Muskeget, it constitutes the Town and County of Nantucket, a combined county/town government that is part of the U.S. state of Massachus ...
for each month,
Sarajevo Sarajevo ( ; cyrl, Сарајево, ; ''see names in other languages'') is the capital and largest city of Bosnia and Herzegovina, with a population of 275,524 in its administrative limits. The Sarajevo metropolitan area including Sarajevo ...
has recorded below-freezing temperatures in every month of the year.


Macaronesia

Macaronesia consists of four archipelagos: The
Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...
, the
Canary Islands The Canary Islands (; es, :es:Canarias, Canarias, ), also known informally as the Canaries, are a Spanish Autonomous communities of Spain, autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to ...
,
Cape Verde , national_anthem = () , official_languages = Portuguese , national_languages = Cape Verdean Creole , capital = Praia , coordinates = , largest_city = capital , demonym ...
and
Madeira ) , anthem = ( en, "Anthem of the Autonomous Region of Madeira") , song_type = Regional anthem , image_map=EU-Portugal_with_Madeira_circled.svg , map_alt=Location of Madeira , map_caption=Location of Madeira , subdivision_type=Sovereign st ...
. At lower altitudes and coastal areas, the Portuguese Azores and Madeira belong to zones 11a/11b and 11b/12a respectively. The Azores range from 9a to 11b and Madeira ranges from 9b to 12a, 9a and 9b found inland on the highest altitudes such as the Mount Pico in the Azores or Pico Ruivo in Madeira. The Spanish
Canary Islands The Canary Islands (; es, :es:Canarias, Canarias, ), also known informally as the Canaries, are a Spanish Autonomous communities of Spain, autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to ...
hardiness zones range from 8a to 12b depending on the location and the altitude. The islands are generally part of zones 11b/12a in lower altitudes and coastal areas, reaching up to 12b in populated coastal parts such as the city of Las Palmas. The lowest hardiness areas are found in Teide National Park being at 8a/8b for its very high altitude. The Teide peak is the highest peak of Macaronesia. The
Cape Verde , national_anthem = () , official_languages = Portuguese , national_languages = Cape Verdean Creole , capital = Praia , coordinates = , largest_city = capital , demonym ...
islands, inside the
Tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also refer ...
, have hardiness zones that range from 12 to 13 in the coastal areas, while the lowest hardiness zone is found in the island of Fogo, in the country's highest peak Pico do Fogo.


American Horticultural Society heat zones

In addition to the USDA Hardiness zones there are
American Horticultural Society The American Horticultural Society (AHS) is a nonprofit, membership-based organization that promotes excellence in American horticulture. It is headquartered at River Farm in Alexandria, Virginia. History Established in 1922, the AHS is one of ...
(AHS) heat zones. The criterion is the average number of days per year when the temperature exceeds . The AHS Heat Zone Map for the US is available on the American Horticultural Society website.


South Africa

South Africa has five horticultural or climatic zones. The zones are defined by minimum temperature.


Effects of climate change

The USDA map published in 2012 shows that most of the US has become a half zone () hotter in winter compared to the 1990 release. Research in 2016 suggests that USDA plant hardiness zones will shift even further northward under
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
.


See also

*
Agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people ...
*
Gardening Gardening is the practice of growing and cultivating plants as part of horticulture. In gardens, ornamental plants are often grown for their flowers, foliage, or overall appearance; useful plants, such as root vegetables, leaf vegetables, frui ...
* Geographical zone * Hardiness (plants) *
Subtropics The subtropical zones or subtropics are geographical and climate zones to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from to approximately 35° nort ...


References


Bibliography

* {{refend


External links


Freeze/Frost data from NOAAPlant Hardiness Data
(Canada)
Plant Hardiness Zones of Canada – Interactive Map
Agricultural terminology Horticulture Climate zones Geographic classifications