Frost resistance zones: understanding and calculation. Natural and climatic zones of Russia What does climate zone 4 mean
01.01.2012
When choosing new plants, pay attention to such a criterion as winter hardiness zones.Having data about your zone, you will be able to judge with a certain probability whether you can grow a particular plant in open ground.
This system (USDA-zoning) is introduced by the US Department of Agriculture but it is also used in Europe.
Hardiness zones are a certain range of temperatures in which the plant stably overwinters.
The Moscow region is traditionally referred to as the 4th zone.
That is, if zone 4 is indicated on an imported plant, it is assumed that this specimen is able to overwinter in conditions, withstanding frosts down to minus 29 degrees.
However, there are many conventions in this topic.
There is convincing evidence of the successful cultivation of plants in the Moscow region classified both in the 5th and even in the 6th zones. For example, according to many reports, ginkgo winters well in the Moscow region, although it is classified as a 5th zone.
Winter hardiness also largely depends not only on the genetic properties of the plant, but also on its current state. Past illnesses, deficiency minerals or too big harvest weaken the living organism, and its resistance decreases. Plants for which proper care, shows the maximum winter hardiness inherent in this species.
Winter hardiness changes throughout the entire hibernation period of the plant: it reaches its peak by the end of deep dormancy (end of the year in middle lane Russia), and then decreases.
The period of transition from hibernation to the growing season is quite difficult. For example, at the beginning of spring, the bark of trees heats up during the day, and at night it cools sharply, which leads to its damage. Temperature fluctuations have a negative impact on the most vulnerable areas fruit trees- the lower parts of the trunks. Trees can be protected by whitewashing trunks at the end of winter.
Microclimatic factors affecting the winter hardiness of plants.
In addition to temperature, there are many additional factors that affect the development of plants: soil type, daylight hours, wind, humidity. It should be taken into account that the microclimate of areas within the climatic zone may not correspond to the baseline values.
Elevations, southern slopes, large reservoirs have a beneficial effect on plant growth, in contrast to lowlands and northern slopes. In the city, as a rule, the temperature is slightly higher than outside the city.
With careful observance of all the rules of agricultural technology, many trees and shrubs can be grown on the territory of colder zones in protected areas.
The plant can be suitable for five and more zones.
If your hardiness zone is colder than what is recommended for planting the selected plant, special care must be taken in deciding where to plant the seedling on the site.
Dry cold wind puts the development of evergreens at risk, as the process of evaporation from the surface of the leaves becomes more intense, and dehydration occurs. To avoid this problem, it is necessary to plant in places protected from the wind and ensure the correct development of the root system. For this, the soil must be deep, loose, permeable. Mulching works well.
wintering difficulties.
IN warm winters with abundant snow cover, plants are threatened with decay - exhaustion in a dark, waterlogged, warm environment, when plants "unscheduled" consume all their nutrients.
Wetting can occur in the lowlands during the period of snow melting or prolonged thaws: melt water is not absorbed into the soil and plants lack oxygen.
The lack of oxygen and mechanical pressures often also occur due to the formation of ice crusts. The formation of an ice crust occurs if, after frequent thaws, very coldy. The crusts are contact (tightly attached) or hanging (practically do not come into contact with plants, they are easy to destroy).
Bulging.
There may be frosts in the absence of snow cover or an autumn drought, or a thaw in which snow water has already been absorbed by the soil. In such conditions, freezing begins at a depth - where there is water. The layer of ice gradually increases and lifts, that is, “bulges out” the upper layers of the soil along with the plants, which leads to the breakage of the roots. Secondary rooting can save the plant from drying out, which can be stimulated with the help of timely rolling of the soil. Crops with roots capable of stretching are resistant to bulging.
Damage from winter drought (at the end of a snowless or little snowy winter with significant solar heating) poses a danger to fruit trees and shrubs in a number of regions of Russia. Under normal conditions, a stable winter cover protects the plant from drying out.
The area in which your garden plot, you can determine yourself - for this you need information about the most low temperatures in your area over the past 10 years (you can choose a longer time period). Then we calculate the arithmetic mean of all values and see what zone number it corresponds to.
Obviously, this method cannot be considered absolutely accurate. For example, anomalous temperature jumps can affect the result of calculations. In addition, the same result can be obtained both with a large spread and with minimal fluctuations in values. It is believed that the territories of central Russia correspond to zone No. 5 and those below.
Below are two tables (table 1-short and more detailed table 2) by which the zone can be determined.
Table 1.
Zone Temperature
1 below - 45°C
2 from -45 to -40°C
3 -40 to -34°C
4 from -34 to -29°C
5 from -29 to -23° С
6 from -23 to -17° С
7 from -17 to -12° С
8 from -12 to -7° С
9 -7 to -1°C
10 from -1 to +5° С
Table 2.
Hardiness zone From To
0 a< -53.9°C
b -51.1°C -53.9°C
1a -48.3°C -51.1°C
b -45.6°C -48.3°C
2 a -42.8°C -45.6°C
b -40°C -42.8°C
3 a -37.2°C -40°C
b -34.4°C -37.2°C
4 a -31.7°C -34.4°C
b -28.9°C -31.7°C
5 a -26.1°C -28.9°C
b -23.3°C -26.1°C
6 a -20.6°C -23.3°C
b -17.8°C -20.6°C
7 a -15°C -17.8°C
b -12.2°C -15°C
8 a -9.4°C -12.2°C
b -6.7°C -9.4°C
9 a -3.9°C -6.7°C
b -1.1°C -3.9°C
10 a +1.7°C -1.1°C
b +1.7°C +4.4°C
11 a +4.4°C +7.2°C
b +7.2°C +10°C
12 a +10°C +12.8°C
b > +12.8°C
According to kr.ru
Garden roses are rather capricious plants with high requirements for the climatic zone of cultivation. In variety descriptions, flower growers often come across such a characteristic as the "USDA zone". To understand what this marking means and how to choose a rose variety, taking into account the climate, is described in the proposed material.
Meaning and Characteristics of USDA Zones
Climate zoning is an artificial division of territories that helps gardeners understand whether a particular plant can withstand certain conditions. The intensity of their growth, abundance of flowering, life expectancy and resistance to diseases depend on the adaptability of roses to the climatic zone.
Climate as a whole is a multicomponent concept. It includes many characteristics: average summer and winter temperatures, rainfall in different time year, number of sunny days per year, length of daylight hours, prevailing winds, etc. Zoning territories taking into account all these parameters is quite difficult, because even within the boundaries of one geographical latitude they can fluctuate a lot. Therefore, a system was adopted that highlights one characteristic - the minimum winter temperatures. So the zonesUSDA - 'these are hardiness zones.
The USDA system was developed by the US Department of Agriculture and today includes 13 main zones with two sub-zones each:
| Main zones and subzones by systemUSDA | Minimum temperatures in winter period, 0 С | |
| I | Ia | Up to -51.1 |
| Ib | Up to -48.3 | |
| II | IIa | Up to -45.6 |
| IIb | Up to -42.8 | |
| III | IIIa | Up to -40 |
| IIIb | Up to -37.2 | |
| IV | IVa | Up to -34.4 |
| IVb | Up to -31.7 | |
| V | Va | Up to -28.9 |
| Vb | Up to -26.1 | |
| VI | VIа | Up to -23.3 |
| VIb | Up to -20.6 | |
| VII | VIIa | Up to -17.8 |
| VIIb | Up to 15 | |
| VIII | VIIIa | Up to -12.4 |
| VIIIb | Up to -9.4 | |
| IX | IXa | Up to -6.7 |
| IXb | Up to -3.9 | |
| X | Xa | Up to -1.1 |
| Xb | Up to +1.7 | |
| XI | XIa | Up to +4.4 |
| XIb | Up to +7.2 | |
| XII | XIIa | Up to +10 |
| XIIb | Up to +12.8 | |
| XIII | XIIIa | Up to +15.6 |
| XIIIb | Up to +18.3 | |
Tip #1 In descriptions of varieties of roses, as a rule, the mainUSDA zone. It indicates only the frost resistance of the variety, however, when buying, it is important to take into account other characteristics. For example, if a rose is suitable for frost resistance, but not suitable for drought resistance, it is better to refrain from purchasing it.
USDA climate zones in Russia
On the territory of Russia there are 9 main frost resistance zones according to USDA. Roughly they are distributed as follows:
First in the region of Yakutia.
Second- in Central Siberia, the Komi Republic.
Third– Eastern and Western Siberia, Kola Peninsula, Kamchatka.
4th- South-Eastern Siberia, Khabarovsk Territory.
Fifth- the middle Volga region, the Urals, the Central European part of Russia, the North-Western part of Russia.
sixth – lower Volga region, Voronezh, Kaliningrad region.
seventh- Rostov-on-Don, northern regions of the Stavropol Territory.
eighth- Astrakhan, Volgograd, the main part of the Stavropol Territory, the mountainous regions of the North Caucasus.
ninth – Krasnodar region, Crimea, foothills of the North Caucasus.
In the Yakutsk region, the coldest point of the Northern Hemisphere is also located - in the area of the village of Oymyakon. Here, winter temperatures drop below -70 0 C.
Tip #2 Global climate change is making its own adjustments to the mapsUSDA. It is difficult to define clear boundaries today. The correct tactic for determining your zone is to collect statistical data on winter temperatures over the past 5-10 years.
Rose Varieties for Different USDA Zones
There are so many varieties of roses today that you can choose the right one for almost any USDA zone, except for the first, with extremely low frosts. For example:
| ZoneUSDA | rose variety | Variety |
| IIb | David Thompson | Hybrid Rose Rugosa |
| IIIb | William Baffin | Canadian rose |
| IV | Prairie Joy | shrab |
| V | Schneewittchen | floribunda group |
| VI | Leonardo da Vinci | floribunda group |
| VII | Yellow Fairy | polyanthus |
| VIII | Amazing Grace | Hybrid Tea |
| IX | Climbing Gold Bunny | Climbing |
Current Questions About USDA Rose Zones
Question number 1. Can a variety recommended for Zone III be grown in USDA Zone II?
Can. A number of agricultural techniques allow you to raise the microclimate in the area by 1 or even 2 zones. First of all, this is a competent selection of a landing site. If you plant a rose under the southern wall of the house, firstly, it will be reliably covered from the cold wind, and secondly, it will be better illuminated and heated by the sun (See also the article ⇒). The second moment is preparation for wintering. Rosa needs to ensure good ripening of the shoots with the help of potash top dressing and reliable winter shelter. Finally, soil conditions play a role. If, when planting, the clay content in the soil is reduced and its humus content is increased, the roses will winter much better.
Question number 2. Will a hardy USDA zone III rose grow in a warm zone VI climate?
Frost-resistant roses are successfully grown in the south. But in this case, it is important to take into account the resistance of the variety not so much to freezing as to damping off. During warm, humid winters root collars some varieties hardy roses can get wet affected by fungi. Therefore, it is important to provide them with excellent drainage. It is better to plant such roses on an elevated place. IN landing pit you need to lay a good baking powder - better not sand, but agroperlite. The trunk circle should be mulched with dry mulch, not prone to waterlogging and caking. It is not necessary to cover roses planted in a zone warmer than recommended for the winter.
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 zone, 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 the trunks of fruit trees in November, shading evergreens with covering material in February or 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 |
Recently, the counters of shops and markets are full of exotic plants for our country. Yes, and familiar cultures are replenished with new varieties and varieties. Sellers assure that all these crops are zoned and perfectly adapted for growing in our difficult climate. But is it really so?
The climate of our country, characterized by warm or even hot summers, but cold and long winters, is naturally not suitable for all flora. Assess the ability of plants to withstand cold winter helps the concept called winter hardiness. Some (mosses and lichens) perfectly tolerate even the lowest winter temperatures, others (birch, oak) can only grow in more benign conditions, and still others (magnolia, oleander) are not at all adapted for harsh winters.
What plants are adapted for our climate knows, perhaps, everyone experienced gardener. But what to do with the novelties of the market, how to find out if the newly acquired green pet will survive the harsh winter? In fact, there is no problem here - reference books, documents and labels of specimens from nurseries indicate the frost resistance zone suitable for the plant. Let's see what it is.
What are frost hardiness zones
Frost resistance (or winter hardiness) zones are climatic regions the globe suitable for growing certain types of plants. They are based on a temperature scale showing the average annual minimum temperature in degrees Celsius or Fahrenheit.
At present, the most complete scale of frost resistance used everywhere is the so-called scale or USDA zones.
USDA zones
The USDA scale was first developed by the US Department of Agriculture for the needs of farmers and horticulturists, and then the proposed zoning began to be used throughout the world. The scale includes 13 zones (from 0 to 12), each of which is divided into 2 more subzones, the boundaries of which were determined on the basis of the minimum average annual temperatures. At first, only the territory of the United States was described, and then other countries. Now all regions of the globe belong to one or another zone on the USDA scale, and all plant species are divided according to their adaptability to different climatic conditions.
For example, a plant described as "zone 10 hardy" means that it can withstand a minimum temperature of -1°C. A more resistant plant, “zone 9 hardy”, can withstand a minimum temperature of -7 °C, etc.
USDA zoning is currently the universal scale of frost resistance used by modern farms. However, it has many shortcomings and does not take into account a number of critical factors, such as:
- Snow cover height. It is known that snow perfectly protects the root system of plants from frost, so crops that freeze in snowless regions can survive well where there is a lot of snow in winter.
[!] Plant breeder from Poland noticed one interesting feature: azaleas dying of cold in Eastern Europe, wintered well in the Moscow region, where the climate is much more severe. It turned out that the rhododendrons were protected by snow, which did not allow the root system to die.
- Temperature changes. Many cultures are afraid not so much of frost as of sudden changes in temperature in winter. A sudden thaw, causing the snow to melt, and an equally sudden cold snap, leads to the death of the roots. That is why a number of plants, such as some types of bamboo, which can withstand severe frosts, cannot survive in our climate.
[!] In the 60s of the last century, due to such a sudden drop in winter temperature (from -1°С to -29°С), the collection of maples of the Botanical Garden of Moscow State University suffered greatly.
- Spring frosts are another factor hindering the cultivation of heat-loving species. In our country, this problem is especially relevant: in the middle lane, frosts can return even at the end of May.
[!] You don't have to look far for examples. The May cold of 2017 killed a significant part of the grapes in the Crimea.
- Average annual rainfall. Humidity is important climatic parameter affecting, among other things, the adaptation of plants. For example, some crops tolerate dry cold air well, but do not survive in humid climates.
- Other factors: the difference between day and night temperatures, terrain (presence of uplands and lowlands), soil types, daylight hours, wind rose, etc.
Russia, divided into USDA climate zones, looks something like this:
Some cities of our country belong to the following frost resistance zones: zone 1 - Tiksi, Batagai, zone 2 - the greater territory of Russia, Krasnoyarsk, Irkutsk, Novosibirsk, zone 3 - Khabarovsk, Magadan, Vorkuta, zone 4 - Moscow and the Moscow region, Vologda, Arkhangelsk , Chelyabinsk, Ufa, zone 5 - St. Petersburg, Vladivostok, Voronezh, Bryansk, Saratov, zone 6 and 7 - Krasnodar.
As for the labels on plants from nurseries, for Moscow and St. Petersburg, you should choose crops acclimatized for zones 1-4, as well as 5a and, partially, 5b.
As you can see, USDA zoning is far from perfect, so work in this direction is constantly ongoing.
Alternatives
The flawed USDA system prompted a search for alternatives. And now they use not only the above concept, but also some others. Firstly, USDA zones have been added to and their number has been significantly increased. In addition, one of the means of determining frost resistance zones was the use of so-called "indicator plants". It is known that the range of some species is strictly limited depending on the climate, and therefore the presence of any indicator plant indicates that the territory belongs to one or another frost resistance zone.
In addition, some countries have developed their own climate maps based on long-term meteorological observations. One of these countries was the UK.
In 2012, the Royal Horticultural Society of the United Kingdom presented their plant hardiness rating. This rating describes all plants found in the UK and is widely used by English growers.
The English system of plant frost resistance consists of 9 parts:
- H1a (more than 15°C) - growing in a greenhouse;
- H1v (from 10 to 15°C) and H1c (from 5 to 10°C) - cultivation on outdoors only in summer;
- H2 (from 1 to 5°C) - crops that can tolerate a slight drop in temperature, but are not resistant to frost;
- H3 (from -5 to 1°C) - crops that tolerate the climate of the coastal regions of Great Britain;
- H4 (from -10 to -5°C) - crops adapted to the climate of most of the UK;
- H5 (from -15 to -10°C) - crops adapted to the climate of most of the UK and withstanding a significant drop in temperature in winter;
- H6 (from -20 to -15 ° С) - frost-resistant crops that can grow throughout Northern Europe;
- H7 (less than -20°C) are the most frost-resistant crops.
Frost resistance zones in the USSR and Russia
In our country, work on determining frost resistance zones began at the beginning of the 20th century, and then continued after the October Revolution. And, although at first the maps were imperfect, and the climatic regions were too generalized, in the 60s the work was continued: the number of zones increased to 42 (up to 60 together with subzones). The work was called "Tree-cultivating regions of the USSR." In addition to zoning, work was also carried out to separate plants found in the USSR according to climatic regions. The list consisted mainly of tree crops, but the number of species included in it is very large - about 700.
The data obtained by Professor AI Kolesnikov, who supervised the work, summarized in the publication "Decorative Dendrology". This book is still relevant today.
FROM detailed description tree-cultural regions of the USSR you can familiarize yourself with.
The work did not stop there, and the detailing of zoning continued. Other factors affecting the winter hardiness of plants began to be taken into account: not only the minimum, but also the average annual temperatures of winter and summer months, average and minimum humidity, evaporation and annual precipitation. The number of frost resistance zones increased to 76, and the plants recommended for each zone were divided into three groups - “main”, “additional” and “auxiliary”:
- the main one is plants that are well acclimatized for the area,
- additional - crops that can grow in the considered climatic zone only under the condition good care(shelters for the winter),
- auxiliary - singly occurring plants.
Unfortunately, serious state research on this topic was no longer carried out, although both the climate and the assortment of plants have changed, and tremendous practical experience has been accumulated. From time to time, individual farms try to compile such maps, but due to lack of resources, their work is limited to individual areas.
How to increase the frost resistance of plants
In conclusion, I would like to give some tips from the practice of gardening. Many crops recommended for more favorable climatic zones, with proper care, it is quite possible to grow here. To improve winter hardiness certain types recommended:
- Protect the root system from frost. This can be done with the help of coniferous spruce branches, dry fallen leaves, peat, sawdust, industrial covering material. Styrofoam, which has high heat-insulating properties, has also proven itself well.
- Cover not only the roots, but also the aerial part of the plant. Of course, it is difficult to protect the crown of powerful tree crops (although some gardeners manage to wrap the lower part of the trunks with cloth or polyethylene), but liana-like species and plants with flexible stems should be carefully laid on the ground and covered.
[!] It is especially important to protect young cultures, whose age is 2-3 years. Them root system not yet fully formed and is located close to the surface of the earth.
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. Broad perspective for the introduction of various foreign crops temperate climate starts from the 5th zone, 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 only be considered in the context of a limited time frame - or for the period of all available on this moment observations (often, this is no more than 60-80 years of history), or within the initially set limits: the last climatic norm - a period of 30 years of observations, or an arbitrarily taken period - 20, 40 or 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 to the frost resistance zone 5b, which is typical only for the microclimate conditions of the city (the total frost resistance zone for the Moscow region will already 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 insufficient for commercial apricot cultivation (varieties derived from the common apricot genotype), or walnut.
One should always distinguish general recommendations on the introduction (introduction) of certain plant species within one climatic region- frost resistance zones, 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 increased sensitivity to environmental conditions that are not typical 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 fully open up only in native conditions. So, for example, depending on the place of growth (nature of naturalization), as well as the source of the seed material, in a situation of full passage of all phases of vegetative development, the manifested frost resistance of the Manchurian walnut, which allows 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
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