Data on frost resistance zones. Climatic zones - determination of cold resistance of plants Usda fifth zone

USDA hardiness zones

The specified climatic zoning of territories is an artificial division of places for growing plants, based on the ability of plants to survive in winter conditions. This division is based on a long-term study of winter temperatures.

The assignment of a plant to a particular zone is based on knowledge of the variety's requirements for growth and development conditions. However, even in the same area climatic conditions are not the same. It is well known that with south side houses are always warmer, and in a place protected from the winds (for example, a courtyard or urban development), even the largest "sissies" can grow. Therefore, the given zoning of plant varieties is rather conditional.
With the help of the correct placement of plants (in a warm and calm place), as well as the use of covering materials (spunbond, foliage, spruce branches, hilling, etc.) and “laying” shoots to the ground for the winter, you can increase the climatic zone of your site by 1-2 units. Improvement of the soil regime also helps in this (for example, the introduction of clay on sandy soils, making organic fertilizers, covering the soil with manure, mulching with sawdust, peat, etc.). Then, for example, in the conditions of the third climatic zone, it is possible to grow varieties belonging to the fourth or fifth zone without any problems. Besides, special events, such as whitewashing trunks fruit trees in November, shading evergreens with covering material in February or from autumn will help to avoid frost and sunburn in conditions of sudden temperature changes and weather changes.

Table of frost resistance zones:

Zone	From	Before
0
1	-45.6 °C	-53.9 °C
2	-40°C	-45.6 °C
3	-34.4°C	-40°C
4	-28.9 °C	-34.4°C
5	-23.3°C	-28.9 °C
6	-17.8 °C	-23.3°C
7	-12.2°C	-17.8 °C
8	-6.7 °C	-12.2°C
9	-1.1°C	-6.7 °C
10	-1.1°C	+4.4 °C
11	+4.4 °C	+10°C
12	>+10°C

The main factor determining the choice of new perennials for a garden, it is a climate. It is especially important to know whether this species will overwinter in a given region or not. In nurseries, a frost hardiness zone is usually indicated for each plant. From it you can find out how low temperatures a plant can withstand and decide whether it is worth buying.

What are hardiness zones?

Initially, the definition of climatic zones for frost resistance was developed by the United States Department of Agriculture (USDA) for the needs Agriculture. 13 climate zones have been identified based on the minimum winter temperatures by region. Then the system was refined and improved. The data is summarized in the following table:

Zone		from	before
0	a	< –53,9 °C
	b	-53.9°C	-51.1°C
1	a	-51.1°C	-48.3°C
	b	-48.3°C	-45.6°C
2	a	-45.6°C	-42.8°C
	b	-42.8°C	-40.0°C
3	a	-40.0°C	-37.2°C
	b	-37.2°C	-34.4°C
4	a	-34.4°C	-31.7°C
	b	-31.7°C	-28.9°C
5	a	-28.9°C	-26.1°C
	b	-26.1°C	-23.3°C
6	a	-23.3°C	-20.6°C
	b	-20.6°C	-17.8°C
7	a	-17.8°C	-15.0°C
	b	-15.0°C	-12.2°C
8	a	-12.2°C	-9.4°C
	b	-9.4°C	-6.7°C
9	a	-6.7°C	-3.9°C
	b	-3.9°C	-1.1°C
10	a	-1.1°C	1.7°C
	b	1.7°C	4.4°C
11	a	4.4°C	7.2°C
	b	7.2°C	10.0°C
12	a	10.0°C	12.8°C
	b	> 12.8°C

All zones in the US and Canada have been marked on the maps, taking into account mountain climate zones and coastal areas. Later, frost resistance zones were also determined for Europe.

For Russia, they are indicated approximately and are not a recommendation for growing certain types of plants. However, every gardener must know which climatic zone of frost resistance his region belongs to, so as not to be disappointed in the spring.

More detailed map winter hardiness zones for the European part of Russia:

for China:

for Ukraine:

for Belarus:

Factors that determine the zone of frost resistance

The specific minimum winter temperatures in the region depend on the geographical latitude, on the relief, on proximity to the ocean and air humidity.

Geographic latitude determines the amount of solar radiation that the earth's surface receives. In the southern regions, it is larger, so the climate is hotter there. But this is not at all the determining factor. By geographical latitude London is located to the north of Kyiv, but in Kyiv there are often twenty-degree frosts in winter and it belongs to the 5th zone, and in the south of England the grass turns green in winter. The south of England is classified as hardiness zone 9 due to its proximity to Atlantic Ocean and the warm Gulf Stream. In Kyiv, the climate is close to continental, with dry summers and frosty winters.

The southern coast of Crimea belongs to zone 7, and the steppe Crimea to zone 6. The mountains protect the coast from northern winds, so palm trees, cypresses, wisteria and magnolias grow on the coast, and in other parts of the peninsula they freeze in winter.

The frost resistance zones of Europe are distributed rather than from north to south, but from west to east - this is how the Atlantic affects the climate. IN Eastern Europe winters are noticeably harsher than in Western.

Local conditions affecting the winter hardiness of plants

Do local conditions always correspond to the climate zone in terms of frost resistance? Many pet owners can answer this question. garden plants. Surely they will confirm that even within their region, some varieties perfectly acclimatize and develop normally in certain areas, and in neighboring ones, literally at a distance of 50 km, there are serious problems with wintering.

This is due to the terrain, the height of the snow cover in winter, and the proximity of large water bodies. For example, Quebec in Canada is in zone 4, but plants grown there are designed for zones 5 or 6. The peculiarity of Quebec is that the height of the snow cover is always high there and there are no large temperature fluctuations. Snow serves reliable protection for plants.

Another example is the small village of Waksmund in the Polish Carpathians, where temperatures often drop to -35°C in winter, where the record for the lowest winter temperatures for the region is -49°C. It is located near Krakow, where the average winter temperature is -5.5°C, and the minimum record was recorded in 1929 and it is only -32°C. The fact is that it is in the area of ​​\u200b\u200bthis village that cold and heavy air masses from the mountains descend down the slopes, creating such a paradox.

Climatic zone and plant features

When choosing new plants for your garden, you should take into account not only the winter hardiness zone, but also the characteristics of these species. Very often, perennials for the 4th frost resistance zone do not withstand more than mild winters 5 or 6 zones. Why is this happening?

When making a decision before buying, it is useful to carefully study the properties of the plant and recommendations for care. An example is the features of growing some ( , ). They often do not tolerate winter, but this is not due to frost. The reason is prolonged thaws. These groundcovers do not like excess moisture in cold soil. If the winter is frosty without thaws, everything is fine; if frosts alternate with thaws, they will not overwinter. The problem can be solved by planting them on slopes where water does not linger.

Russia is the largest state in terms of area, which is territorially located on the continent of Eurasia. The Russian Federation has a huge extent from north to south and from west to east. Its climatic conditions are quite diverse.

What are climatic zones?

Main characteristic separate zones is the climate - the interaction of temperature, humidity, air currents, solar intensity. Natural-territorial complexes have the character of latitudinal or sublatitudinal bands encircling the entire territory the globe. They differ in climatic conditions, soil cover, relief features, representatives of flora and fauna. On the territory of Russia, climatic zoning is applied. The state is located in the following zones:

• arctic;
• subarctic;
• moderate;
• subtropical.

Territorial division

The first belt covers the islands, as well as the coast of the Arctic Ocean. In the territory located from the East European Plain and Western Siberia to 60 degrees north latitude, a subarctic climate dominates. Most of Russia is located in the temperate zone. Which can be divided into:

• temperate continental,
• continental,
• sharply continental,
• monsoon.

The territory of the European part of Russia is located in the temperate continental climate zone. Western Siberia and the territory of the extreme southeast of the East European Plain are located in the zone of the continental climatic zone. Territory Central Siberia- a zone of sharply continental belt. For Far East characterized by a monsoonal climate.

The smallest is the territory located in the subtropical climate zone. This is the Black Sea coast.

The delimitation of the territory of Russia

The climatic zones of Russia can be determined using a special temperature map. The territory on the map is divided into regions with similar natural conditions. Each area is characterized by an average annual minimum temperature range. The dates of the first autumn and last spring frosts can also be additionally indicated.

The natural and climatic zones of Russia are located in the temperature range from minus five in the warmest regions to minus sixty in the coldest. You can determine the region in which the desired site is located simply by looking at the map. Or, if greater accuracy is required, you can calculate it yourself by obtaining the arithmetic mean of the temperatures in the selected zone over the past ten or more years.

Eternal Frost Zone

The first climatic zone of Russia is tundra or arctic and subarctic. Most of the Republic of Sakha (Yakutia) can be attributed to it. So, in its eastern part, average annual temperatures prevail, reaching minus forty-five degrees Celsius. The 1st climatic zone of Russia is characterized by very cold, long winters with little snow and short, relatively warm summers. This zone is characterized by a short frost-free period. This condition has a huge impact on the development of the flora. Dwarf trees and shrubs grow in this zone.

For growing crops, this climatic zone provides only a few warm summer months, during which the permafrost retreats and frees up small plots of land for planting for the most stubborn and resourceful farmers. But nonetheless wide use greenhouses, frost-resistant and early maturing crops makes it possible to harvest almost all known vegetables and fruits even in these harsh conditions.

Taiga climatic zone of Russia

A vast territory can be attributed to the second climatic zone. This is almost the entire territory located between the European part in the west and the third climatic zone in the east, stretching along the entire coast. This zone extends from Karelia to Kamchatka. Winter temperatures are moderate. However, the territory located in the east of this zone has more severe winters. So, in Eastern Siberia, severe snowy winter period accompanied by a drop in air temperature to minus forty or forty-five degrees Celsius. The climatic zone of Russia 2 is characterized by very severe weather conditions. Increased dampness contributes to soil cover with mosses. The soil is cold and wet. Near water bodies, the soil temperature is somewhat warmer, but even this is not enough for the production of crops. Also a complicating factor can be considered a strong freezing of the earth in winter.

Forest-steppe and steppe climatic zones of Russia

Climate zones three and four include the most densely populated part of the country. This strip is located all the way from the Murmansk and Arkhangelsk regions practically through the entire European part of Russia to the border with Kazakhstan and ends in the Altai Republic.

Also, the 3rd climatic zone of Russia captures the Far Eastern regions of the country along the entire eastern coast and includes parts of the regions. These are the Chukotka Autonomous Okrug, Kamchatka Territory, Magadan Region, Khabarovsk region, Sakhalin Region, Primorsky Region and Jewish Autonomous region. The monsoon climate prevails in this area. Cold snowy winters give way to cool and wet summer period. Frequent fogs and typhoons are typical.

Steppe - 4th climatic zone of Russia. Territorially includes the Lower and Middle Volga regions, North Caucasus, Southern Urals. As well as the southern regions of Western and Eastern Siberia. This zone is characterized by cold winters and dry summers. In central Russia, one can single out the territory adjacent to the shores of Lake Baikal. Here, due to geographical factors, a kind of temperature oasis has formed.

Dry steppe climate zone

This region is geographically located from the Eastern Ciscaucasia to the Sub-Ural Plateau. Also, the fifth climatic zone includes areas of the Kulunda steppe and territories located in the intermountain basins of Tuva and Transbaikalia. The area is characterized by dry summers with moderate temperatures. Winter frosts are heterogeneous throughout the territory. In the eastern regions of the fifth zone, more severe winters are observed.

Sixth-ninth climatic zones

Based on the map of climatic zones in Russia, built on long-term observations and analysis of temperature regimes various parts country, we can say that the entire territory of the country is located in the temperature regions from the first to the ninth.

Climate zones Russia 6-9 include mainly the southwestern regions of the country. These natural complexes can be characterized as follows:

• 6 - desert-steppe;
• 7-desert;
• 8-foothill semi-desert;
• 9-mountain.

The belt extending from the sixth to the ninth zone provides the most favorable conditions on Russian territory. The southern coastal region along the Caspian Sea can be assigned to zone seven, while the warmest zone is six.

The southeastern region of the Russian Plain and part of the Caspian Lowland are occupied by deserts and semi-deserts. These climatic zones of Russia are characterized by high summer temperatures and low ones in winter. A small amount of precipitation has an impact on the aridity of the climate. This zone is characterized by drought-resistant representatives of the flora.

In the zone of deserts and semi-deserts special place occupies the region of the Volga delta and the Akhtuba floodplain. The life-giving moisture of the river turns the territory into a green oasis.

The warm mild climate of the Caucasus makes it possible to include this territory in zones nine and eight. They can be described as quite soft and warm winter. The temperature regime of this period practically does not go into the negative temperature range. This factor contributes to the rich diversity of vegetation.

In conclusion

The climatic zones of Russia are diverse. Knowledge about each of them is indispensable for Everyday life and are used in a wide variety of industries. These or other natural conditions impose certain restrictions both during construction and when using this or that equipment. When administering economic activity the climatic conditions of the zones must be taken into account. The nature of Russia continuously challenges man, trying to test his strong-willed and spiritual qualities. But no doubt whatever difficult conditions no matter what dangers lurk, a person will always find rational solution and a way out of a difficult situation, and the earth will be covered with sprouts of young plants, new buildings will appear, and nature will submit to man.

The individual characteristics of the development of each plant, as well as its distribution area, are primarily determined by the main characteristics of the environment, such as temperature and precipitation. Therefore, when acquiring new plants for the garden, it is very important to determine their need for the amount of heat needed during the growing season, as well as the conditions temperature regime during dormancy, for favorable wintering and successful breeding. Such indicators for plants are: cold resistance, frost resistance and winter hardiness.

Cold resistance and frost resistance of plants reflects their viability under low temperatures: cold resistance - up to 0 ° C, and frost resistance - from 0 ° C and below.

The winter hardiness of plants is a kind of indicator of the result of wintering plants, reflecting their reaction to the sum of any changes in environmental characteristics in winter: precipitation, wind, icing, thaws, frosts.

Freeze or NOT freeze...

By combining plant species according to their temperature requirements, nurseries various countries, schematic maps have been created, according to which it is possible to determine the frost resistance of representatives of a particular species, depending on the region of growth. Each of the zones marked on the map falls within the temperature range characteristic for the viability of the determined plant species, taking into account a short-term decrease in the lower temperatures that are safe for this species.

However, it should be noted that in any region tied to a certain frost resistance zone, there may be exceptions not only in terms of climatic characteristics (as a microclimate), but also depending on the growing conditions of a particular plant. For example, the same species, tied to the same zone, grown on an open hillside, can freeze out, while its fellow, on the edge of the forest, calmly overwinter under leaf litter. In addition, the mapping of plant hardiness is based on the readings of the lower temperatures of the area over the past decade, which means that the figures obtained in the next decade may be different. Thus, when determining the frost resistance of plants according to the map, one should not forget that such a division - conditionally and completely rely on it - is impossible. It is better to collect as much information as possible from various sources, talking on gardening forums, visiting flower growers' websites, as well as from printed publications: books, newspapers and magazines. However, in this case, it must be borne in mind that some varieties of the same species may differ significantly in frost resistance.

Hardiness zones

1st — from -46°C and below

2nd - from -37ºС to -46ºС

3rd - from -34ºС to -37ºС

4th - from -28ºС to -34°С

5th - from -23°С to -28°С

6th - from -18°С to -23°С

7th — from -12°С to -18°С

8th — from -7° to -12°С

And suddenly it overwinter...

In any case, choosing for your garden plants recommended for areas located to the south, you can try to compensate for the lack of heat by preparing conditions in advance aimed at successful wintering new candidate. Such measures include: feeding plants with potash fertilizers (in August - September), increasing air humidity (spraying plants, planting close to natural and), improving illumination and hardening.

True, if everything is clear with illumination (you just need to choose the brightest place in the garden), then hardening is a lengthy process that requires a lot of time and individual approach to every plant. The success of this procedure will be complete only when properly combined with other methods of care: timely transplantation and correct pruning plants, the use of fertilizers, systematic and high-quality watering. And all this in combination with normal weather conditions. Under adverse environmental conditions, most representatives of the flora are generally able to go into a state of forced rest, while maintaining viability, which in itself is not very good, because in this case, a weakened and unprepared for winter plant can simply die as a result of wintering. This is especially true for heat-loving southerners - sometimes a period of relative rest is observed in them even with slight drops in temperature. That is why, for example, roses give gardeners so much trouble - during thaws, they quickly begin to wake up and release leaves, which then freeze slightly. As for plants native to areas with frosty winters, for such representatives, a state of deep dormancy is a common phenomenon caused by necessity, but this does not save them from return frosts, to which, however, most plants as a whole are subject.

We increase winter hardiness

But if return frosts, despite the cold resistance of plants, can damage the buds, flowers and leaves of a specimen of any age, then the stems, roots and rhizomes of well-rooted plants suffer less with age. The growing bark becomes more durable, and penetrating deep into the ground, root system not only freezes less, but also better provides the entire plant with nutrients, strengthening its immunity and increasing winter hardiness. Given this circumstance, young plants, especially those planted in autumn, must be carefully covered even in southern regions Russia. This is especially true for wintergreen and evergreen species wintering under snow. In snowless winters, they definitely need it, which, in the case of tall specimens, is not easy to build. It should be noted that the snow cover generally facilitates wintering for many plants. Its presence protects the soil surface from thawing during short-term thaws, thereby reducing the risk of damage to the root system from sudden temperature changes; although an abundance of snow can threaten any plants with elementary decay due to the fact that melt water stagnates near the roots, simply not having time to soak into the frozen ground.

Sometimes it happens…

Having acclimatized, some species try to adapt to new conditions, which may affect their external phenological characteristics. For example, shrubs that freeze during wintering, to the ground surface, such shrubs as large-leaved hydrangea, and, under more severe wintering conditions, become semi-shrubs, and arctic cinquefoil leaves, introduced into a warmer region, lose part of the dense pubescence covering their leaves.

PLANT GROUPS BY FROST TOLERANCE	PLANTS NAME
Particularly frost-resistant species from -35°C	birch drooping- Betula pendula elderberry red– Sambucus racemosa Derain white– Cornus alba Derain blood red– Cornus sanguinea Caragana treelike– Caragana arborescens Kostenets hairy- Asplenium trichomanes Linden— Tilia Siberian larch– Larix sibirica Japanese leaflet - Phyllitis japonica Goof silver- Elaeagnus commutata penstemon brilliant– Penstemon nitidus Penstemon hard-haired - Penstemon hirsutus foxglove penstemon— Penstemon digitalis Penstemon vertical— Penstemon strictus Rosa femoralis— Rosa pimpinellifolia Smolevka stemless- Silene acaulis Sorbarony alpine– Sorbaronia alpina
Frost-resistant species from -25°С to -35°С	Armeria maritime- Armeria maritime Common privet- Ligustrum vulgare common hawthorn– Crataegus oxyacantha Hamamelis virginiana-Hamamelis virginiana Double source reed - Phalaroides arundinacea Imperata cylindrical— Imperata cylindrica Viburnum ordinary– Viburnum opulus scalloped chestnut, or American- Castanea Dentata Kochedyzhnik female- Athyrium filix-femma meadow foxtail– Alopecurus pratensis magnolia siebold- Magnolia sieboldii Miscanthus giant- Miscanthus "Giganteus" miscanthus sinensis, or Chinese reed- Miscanthus sinensis Soapweed officinalis- Saponaria officinalis Amethyst fescue- Festuca amethistina Common bracken- Pteridium - aquilinum foxtail pennisetum- Pennisetum alopecuroides Penstemon bearded-Penstemon barbatus penstemon sprawling or serrated– Penstemon diffusus rose wrinkled— Rosa rugosa dog rose— Rosa canina Lilac Hungarian— Syringa josikaea Common lilac— Syringa Vulgaris Pine small-flowered - Pinus Parviflora variety "Hogoromo" Yew canadian- Taxus canadensis Chaenomeles japanese, or japonica- Chaenomeles Japonica
Non-frost-resistant species from -17°С to -23°С	Buddleya alternate-leaved- Buddleja alternifolia Wolfberry Gutta- Daphne x Houtteana Gledichia three-thorned - Gleditsia triacanthos Wisteria profusely flowering, or many-flowered- Wisteria floribunda Rough action - Deutzia scabra Honeysuckle brilliant– Lonicera nitida Imperata cylindrical— Imperata cylindrica Crested chestnut, or Japanese- Castanea Crenata himalayan cedar- Cedrus deodara Cortaderia Sello, or Pampas grass-Cortaderia Selloana (cultivar "Andes Silver") Tulip Liriodendron, or tulip tree-Liriodendrontulipifera Holly holly– Ilex aquifolium oriental plane tree, or Chinar-Platanus orientalis Plum serrate— Prunus serrulata Yew berry-taxus baccata
Heat-loving species from -12°С to -17°С	Araucaria Chilean- Araucaria araucana Wolfberry odorous, or fragrant - Daphne odorata wolfberry silky- Daphne sericea Chinese wisteria - Wisteriachinensis Maiden's grapes are three-pointed, or ivy grapes- Parthenocissus tricuspidata Cork oak- Quercus suber Itea virginskaya— Itea virginica Kamasis rooting,or Tekoma taking root-Campsis radicans Campsis grandiflora, or Chinese- Campsis grandiflora Atlas cedar- Cedrus Atlantica Lebanese cedar— Cedrus libani cypress evergreen-Cupressus sempervirens . Palm maple or fan- Acer palmatum meadow foxtail– Alopecurus pratensis magnolia grandiflora- Magnolia grandiflora Common almond- Prunus communis Sisyurhynchus Bermuda- Sisyrinchium bermudianum

2012, . All rights reserved.

Zoning cultivated plants, is directly related to the definition of the so-called frost resistance zones - climatic regions, to which they can correspond, as acceptable, from the position of laying extensive (industrial) plantations. This concept is more rigorous than the general possibility for the introduction various kinds plants, which allows more extensive experiments in a favorable microclimate.

At the moment, the generally accepted international (American) classification is the USDA zones, containing 11 such gradients with transitional subzones a) and b) (), which, despite its limited flexibility, is still quite often used in our country as a guide.
Most of the territory of the temperate zone (middle zone), with active agricultural activity, fits into the indicators of 3-7 climatic zones of frost resistance. A broad perspective for the introduction of various foreign crops of a temperate climate begins with zone 5, which corresponds to the scale of the average of the absolute minimums: −23.3 °C .. −28.9 °C

There is confusion in understanding these critical indicators for determining frost resistance zones, which are used in agrometeorology in agroclimatic zoning.
First fundamental design parameter- this is an indicator of the absolute annual minimum, characterizing the short-term (from several hours or more) setting of cold fronts, which can lead to significant freezing or complete death of the plant. It can be considered only in the context of a limited time frame - either for the period of all currently available observations (often, this is no more than 60-80 years of history), or within the initially set framework: the last climate normal - a period of 30 years of observations, or arbitrarily the taken term - in 20, 40 and more years. To take into account the latest dynamics of climate change, a period of up to 10-20 years is considered. Given the above, an answer in the spirit of “we don’t have -40” is not correct by definition, in the general case, such words do not characterize anything.
More indicative is another calculated parameter - the average of the absolute minimums (as a rule, it is 1.5 times less than the previous indicator). For its calculation, absolute minimums are taken for each year, for required period(as a rule, over the last 10-20 years of observations) and are averaged. This parameter is taken as the unit of account when determining USDA zones.

Consider an example.
Let's take the data of the absolute minimum (indicator Tn) according to the State botanical garden(GBS) of Moscow (the observation station at the All-Russian Exhibition Center is located a few kilometers from the southern entrance), as a data source we will use the resource - http://rp5.ru/, look in the sections: Weather archive at the weather station / Weather statistics:
2005 .. -21.5 °C
2006 .. -30.8 °C
2007 .. -23.0 °C
2008 .. -18.3 °C
2009 .. -22.1 °C
2010 .. -25.9 °C
2011 .. -26.4 °C
2012 .. -28.5 °C
2013 .. -18.3 °C
2014 .. -25.4 °C

We get: the average of the absolute minimums over the last 10 years of observations will be (add all the values ​​\u200b\u200band divide by 10): -24 ° C
According to the table of values, we determine for the GBS of Moscow the correspondence 5b of the frost resistance zone, which is typical only for the microclimate conditions of the city ( common area frost resistance for the Moscow region will be an order of magnitude lower).

This zone of frost resistance, if we take into account the latest climatic norm - 30 years of observations, passes, approximately, along the border: Minsk - Gomel - Bryansk - Kursk - Belgorod - Voronezh, which is the border, for example, of a possible industrial culture of sweet cherries, but what else not sufficient for commercial apricot cultivation (varieties derived from the common apricot genotype), or walnut.
One should always distinguish between general recommendations for the introduction (introduction) certain types plants within the same climatic region - the frost resistance zone, and the possibility of a specific microclimate. As a rule, within one generalized zone of frost resistance, one can always find (identify): both more favorable conditions, already transitional, for the next - more favorable neighboring zone, and conditions with burdens, which should be taken adjusted for one zone below. Also, there is not the same thing, the frost resistance of a tree considered as part of a forest biocenosis (forest population) and a separate open personal plot. The forest, in itself, is already the fundamental basis for the formation of the microclimate and other factors that contribute to a more adequate acclimatization of the species.
It should be taken into account that many plants from other regions show an increased sensitivity to environmental conditions that are uncharacteristic for them (humidity regimes, solar radiation, the nature of the change of seasons, etc.), which affects, among other things, the ability to unleash the full potential of inherent genotypic frost resistance. For this reason, often, in foreign nurseries, in relation to such foreign crops, two zones of frost resistance are indicated simultaneously - one for natural conditions growth (within its distribution area), and the second - in the introduction of specific local conditions, which, nominally (by default), is set to -1 zone below.

Work on reseeding (reproduction in generations) under new conditions of introduced breeds, as a rule, serves the purpose of normalizing (opening the full potential) of genotypically inherent frost resistance, which is a realistic task for many plants. But still, this reserve should not be exaggerated unnecessarily. In general, it cannot be higher than frost resistance specific type, which manifests itself in natural conditions along the northern border of its distribution, and for sure, it can be most fully revealed only in native conditions. So, for example, depending on the place of growth (nature of naturalization), as well as the source of seed material, in a situation of full passage of all phases of vegetation development, the manifested frost resistance of the Manchurian walnut, allowing it to go through the stage of winter dormancy without significant damage to the aerial part, can vary from - 44 °C to -52 °C and more degrees. At the same time, the ability, let's move on to the example of a walnut, to endure winters with temperatures down to -40 ° C in places of industrial culture (south of Ukraine, for example), and somewhere in the Moscow region, is completely different.
It would be more correct, which is recommended by many reference books, when determining frost resistance zones, to take into account another important interconnected indicator - the sum of active temperatures for growing season(for the temperate zone, most often they are guided by the sum of positive temperatures over +10 ° C), but this is a topic for a separate discussion.

Mar 3, 2014 Alexey