USDA hardiness zones
The specified climatic zoning of territories is an artificial division of plant growing areas based on the ability of plants to survive in winter conditions. This division is based on years of study of winter temperatures.
The assignment of a plant to a particular zone is made on the basis of knowledge about the requirements of the variety for the conditions of growth and development. However, even in the same zone climatic conditions are not the same. It is well known that the south side of the house is always warmer, and in a place protected from the winds (for example, a courtyard or city buildings), even the biggest "sissies" can grow. Therefore, the given zoning of plant varieties is rather arbitrary.
By using correct placement plants (in a warm and windless 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. It also helps to improve the soil regime (for example, the introduction of clay on sandy soils, the introduction of organic fertilizers, covering the soil with manure, mulching with sawdust, peat, etc.). Then, for example, under the conditions of the third climatic zone you can easily grow varieties belonging to the fourth or fifth zone. In addition, special events such as whitewashing of trunks fruit trees in November, shading of evergreens with covering material in February or in autumn will help to avoid frost damage and sunburn in conditions sharp drops temperatures and weather changes.
Frost resistance zones table:
| 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 |
Zoning cultivated plants, is directly related to the definition of the so-called frost resistance zones - climatic regions to which they can correspond, as permissible, from the point of view of laying extensive (industrial) plantations. This concept is stricter than the general introduction option. different types plants, which allows for 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 transition subzones a) and b) (), which, despite its limited flexibility, is still often used in our country as a guideline.
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 cultures of a temperate climate starts from zone 5, which corresponds to the scale of the average of the absolute minima: −23.3 ° C .. −28.9 ° C
There is confusion in the understanding of these critical indicators for determining frost resistance zones that are used in agrometeorology for agroclimatic zoning.
The first fundamental calculated parameter is the indicator of the absolute annual minimum, which characterizes the short-term (from several hours or more) entry 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 - or for the period of all available on this moment observations (often, this is no more than 60-80 years of history), either within the initially specified framework: the last climatic norm - a period of 30 years of observations, or an arbitrary time period - 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. Taking into account the above, the 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). To calculate it, the 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 a unit of account when defining USDA zones.
Let's look at an example.
Let's take the data of the absolute minimum (Tn indicator) for 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 meteorological 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 and divide by 10): -24 ° C
According to the table of values, we determine for the Moscow GBS compliance with the 5b frost resistance zone, which is characteristic only for the city microclimate conditions (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 last 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 crop of sweet cherry, but what else insufficient for industrial culture of apricot (varieties obtained on the basis of the common apricot genotype), or walnut.
One should always distinguish general recommendations on the introduction (introduction) of certain plant species within the same climatic region - frost resistance zone, and the possibility of a specific microclimate. As a rule, within the framework of one generalized zone of frost resistance, it is always possible to find (highlight): both conditions are more favorable, already transitional, for the next more favorable neighboring zone, and conditions with burden, which should be perceived with a correction for one zone below. Also, it 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, about itself, is already a fundamental basis for the formation of a microclimate and other factors that contribute to a more adequate acclimatization of the species.
It should be borne in mind that many foreign plants exhibit increased sensitivity to environmental conditions uncharacteristic for them (moisture regimes, solar radiation, the nature of the change of seasons, etc.), which affects, among other things, the ability to reveal the full potential of the inherent genotypic frost resistance. For this reason, often in foreign nurseries, in relation to such foreign crops, two zones of frost resistance are designated 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 lower.
The work on reseeding (reproduction in generations) in new conditions of introduced breeds, as a rule, serves the purpose of normalizing (revealing the full potential) of genotypically inherent frost resistance, which is a realistic task for many plants. But still, this reserve should not be excessively exaggerated. In the general case, it cannot be higher than the frost resistance of a particular species, which manifests itself in natural conditions along the northern border of its distribution, and certainly, 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 seed material, in a situation of full passage of all phases of vegetative development, the manifested frost resistance of the Manchurian nut, which allows it to pass the stage of winter dormancy without significant damage to the aboveground 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 (southern 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 interrelated indicator - the sum of active temperatures for the growing season (for the temperate zone, most often they are guided by the sum of positive temperatures above +10 ° C), but this is already a topic for a separate conversation.
Mar 3, 2014 Alexey
The main factor determining the choice of new perennial plants for a garden, it is a climate. It is especially important to know whether this species overwinters in a given region or not. In nurseries, a frost resistance zone is usually indicated for each plant. From it you can find out how low temperatures the plant can withstand and decide whether to buy it.
What are frost resistance zones?
Initially, the definition of climatic zones for frost resistance was developed by the United States Department of Agriculture (USDA) for the needs of Agriculture... Thirteen climatic 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 areas in the United States and Canada have been mapped taking into account mountain climates and coastal areas. Later, frost resistance zones were determined for Europe.
For Russia, they are indicated approximately and are not a recommendation for growing certain types of plants. Nevertheless, every gardener must definitely know which climatic zone of frost resistance his region belongs to, so as not to experience disappointment in the spring.
More detailed map winter hardiness zones for the European part of Russia:
for China:
for Ukraine:
for Belarus:
Factors determining the frost resistance zone
The specific minimum winter temperatures in the region depend on the geographical latitude, on the relief, on the 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 there is hotter. But this is not the determining factor at all. By geographic latitude London is located north of Kiev, but in Kiev, in winter there are often twenty-degree frosts and it belongs to zone 5, and in the south of England the grass turns green in winter. The south of England belongs to the frost resistance zone 9 due to its proximity to Atlantic Ocean and warm current Gulf Stream. In Kiev, the climate is close to continental, with dry summers and frosty winters.
The southern coast of the Crimea belongs to the 7th zone, and the steppe Crimea to 6. The mountains protect the coast from the northern winds, therefore, palm trees, cypresses, wisteria and magnolias grow on the coast, and in other parts of the peninsula they freeze out in winter.
The frost-hardiness zones of Europe are rather distributed not from north to south, but from west to east - this is how the Atlantic influences the climate. V Eastern Europe winters are noticeably more severe than in Western.
Local conditions affecting the winter hardiness of plants
Do local conditions always correspond to the climatic zone in terms of frost resistance? Many nursery owners can answer this question. garden plants... Surely they will confirm that even within their region, some varieties are perfectly acclimatized and develop normally in certain areas, and in neighboring, 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 bodies of water. For example, Quebec in Canada is in zone 4, but plants are grown there 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 fluctuations in temperature. Snow serves reliable protection for plants.
Another example is the small village of Waxmund in the Polish Carpathians, where winter temperatures often drop to -35 ° C, 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 this 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 features of these species. Very often, perennials for the 4 frost resistance zones do not withstand more 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 cultivation features of some (,). They often cannot stand winter, but this is not due to frost. The reason is long thaws. These ground covers 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.
01.01.2012
When choosing new plants, pay attention to such a criterion as winter hardiness zones.Having data about your zone, you can, with a certain probability, judge whether you can grow a particular plant in open ground.
This system (USDA-zoning) was introduced by the US Department of Agriculture, but it is also used in Europe.
Hardiness zones are a certain temperature range in which the plant overwinters steadily.
The Moscow region is traditionally referred to the 4th zone.
That is, if the imported plant indicates - zone 4, 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 assigned to both the 5th and even the 6th zones. For example, according to many reports, ginkgo winters well in the Moscow region, although it belongs to the 5th zone.
Winter hardiness also largely depends not only on genetic properties plants, but also on its state at the moment. Past illnesses, lack of minerals or too much big harvest weaken a living organism, and its resistance decreases. Plants for which it is carried out proper care, shows the maximum winter hardiness inherent in this species.
Winter hardiness changes during the entire period of hibernation of the plant: it reaches its peak by the time of the end of deep dormancy (the end of the year at middle lane Russia) and then decreases.
The transition period from hibernation in the growing season is rather 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 changes negatively affect the most vulnerable areas of fruit trees - the lower parts of the trunks. You can protect trees by whitewashing the 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 plant development: soil type, daylight hours, wind, humidity. It should be borne in mind that the microclimate of areas within the climatic zone may not correspond to the baseline values.
Uplands, southern slopes, large bodies of water have a beneficial effect on plant growth as opposed 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 in colder zones in protected areas.
The plant can be suitable for five and more zones.
If your hardiness zone is colder than the one recommended for planting the selected plant, special care must be taken in deciding where to plant the seedling on the site.
Dry cold winds jeopardize the development of evergreens as evaporation from the leaf surface 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 gives a good effect.
Difficulties of wintering.
V warm winters with abundant snow cover, plants are threatened by damping-out - depletion in a dark, waterlogged, warm environment, when plants "unscheduled" consume all their nutrients.
Soaking can occur in lowlands during snowmelt or prolonged thaws: melt water is not absorbed into the soil and plants lack oxygen.
Lack of oxygen and mechanical pressure is often also due to the formation of ice crusts. The formation of an ice crust occurs when after frequent thaws occur very coldy... The crusts are contact (tight) 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 rises, that is, "sticks out" the upper layers of the soil together with the plants, which leads to the breakage of the roots. Secondary rooting can save the plant from drying out, which can be stimulated by timely packing 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) is a danger to fruit trees and shrubs in a number of regions of Russia. Under normal conditions, the plant is protected from drying out by a stable winter cover.
The area in which your garden plot, you can determine it 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 frame). Then we calculate the arithmetic average of all values and see which zone number it corresponds to.
It's obvious that this method cannot be considered absolutely accurate. For example, abnormal temperature fluctuations can affect the results 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 territory of central Russia corresponds to zone 5 and those below.
Below are two tables (table1 is a short and more detailed table2), by which you can determine the zone.
Table 1.
Zone Temperature
1 below - 45 ° С
2 from -45 to -40 ° С
3 from -40 to -34 ° С
4 from -34 to -29 ° С
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 from -7 to -1 ° С
10 from -1 to + 5 ° С
Table 2.
Winter hardiness zone From To
0 a< -53.9°C
b -51.1 ° C -53.9 ° C
1 a -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
Based on materials from kr.ru
V recent times the counters of shops and markets are full of exotic plants for our country. And familiar crops are being replenished with new varieties and varieties. Sellers assure that all these crops are regionalized 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, of course, 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 grow only in more benign conditions, but still others (magnolia, oleander) are not at all adapted for harsh winters.
What plants are adapted for our climate, perhaps everyone knows 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 - in the reference books, documents and on the labels of specimens from nurseries, the frost resistance zone suitable for the plant is indicated. Let's see what it is.
What are frost resistance zones
Zones of frost resistance (or winter hardiness) are climatic regions the globe suitable for growing certain types of plants. They are based on a temperature scale showing the annual average minimum temperature in degrees Celsius or Fahrenheit.
Currently, the most complete scale of frost resistance, used everywhere, is the so-called USDA scale or zones.
USDA Zones
The USDA scale was first developed by the USDA for the needs of farmers and crop farmers, and then the proposed zoning began to be used around 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 based on 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 according to the USDA scale, and all plant species are divided according to their adaptability to different climatic conditions.
For example, a plant described as "hardy to zone 10" means it can withstand a minimum temperature of -1 ° C. A more resistant plant that is "hardy to zone 9" can withstand a minimum temperature of -7 ° C, etc.
Today USDA zoning is a universal scale of frost resistance used by modern farms. However, it has many disadvantages and does not take into account whole line critical factors, such as:
- Snow depth. It is known that snow perfectly protects the root system of plants from frost, therefore, crops that freeze in snowless regions can survive well where there is a lot of snow in winter.
[!] A 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 harsher. 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 temperature changes in winter. A sudden thaw, causing the snow to melt, and an equally sudden cold snap, leads to the death of the roots. This is why a number of plants, such as some bamboos that can withstand severe frosts, cannot survive in our climate.
[!] In the 60s of the last century, due to such a sudden drop winter temperature(from -1 ° С to -29 ° С) the maple collection of the botanical garden of Moscow State University was badly damaged.
- Spring frosts are another factor holding back the cultivation of thermophilic species. In our country, this problem is especially urgent: in the middle lane, frosts can return even at the end of May.
[!] You don't have to go far for examples. The cold of May 2017 killed a significant part of the grapes in Crimea.
- Average annual rainfall. Humidity is an important climatic parameter that affects, 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 (the presence of hills and lowlands), soil types, daylight hours, wind rose, etc.
Russia, divided into USDA climatic zones, looks something like this:
Some cities of our country belong to the following frost resistance zones: zone 1 - Tiksi, Batagay, 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 the search for alternatives. And now they use not only the above concept, but also some others. Firstly, the USDA zones have been supplemented, and their number has been significantly increased. In addition, one of the means for determining the zones of frost resistance was the use of the 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 zone of frost resistance.
In addition, some countries have developed their own climate maps based on long-term meteorological observations. Great Britain became one of these countries.
In 2012, the Royal Horticultural Society of the United Kingdom presented its plant frost resistance rating. This rating describes all plants found in the UK and is widely used by English gardeners.
The English system of plant frost resistance consists of 9 parts:
- H1a (more than 15 ° C) - growing in a greenhouse;
- Н1в (from 10 to 15 ° С) and H1c (from 5 to 10 ° С) - outdoor cultivation only in summer;
- H2 (from 1 to 5 ° C) - crops that can withstand 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;
- Н4 (-10 to -5 ° С) - crops adapted to the climate of most of Great Britain;
- H5 (-15 to -10 ° C) - crops adapted to the climate of most of the UK and withstanding a significant drop in temperature in winter;
- Н6 (from -20 to - 15 ° С) - frost-resistant crops capable of growing throughout Northern Europe;
- Н7 (less than -20 ° С) - the most frost-resistant crops.
Frost resistance zones in the USSR and Russia
In our country, work to determine the zones of frost resistance began at the beginning of the 20th century, and then continued after October revolution... And, although at the beginning 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 named "Wood-cultivated regions of the USSR". In addition to zoning, work was carried out to divide the plants found in the USSR by climatic regions. The list consisted mainly of woody crops, but the number of species included in it is very large - about 700.
Professor AI Kolesnikov, who supervised the work, summarized the obtained data in the publication "Decorative Dendrology". This book has not lost its relevance to this day.
WITH detailed description tree-cultural regions of the USSR you can familiarize yourself with.
The work did not stop there, but zoning detailing continued. Other factors influencing the winter hardiness of plants began to be taken into account: not only the minimum, but also the average annual temperatures of the winter and summer months, the 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 - plants well acclimatized for the area,
- additional - crops capable of growing in the considered climatic zone only under the condition good care(shelter for the winter),
- auxiliary - single plants.
Unfortunately, serious government research on this topic was no longer carried out, although both the climate and the range of plants have changed, and enormous practical experience has been accumulated. From time to time, such maps are attempted to be drawn up by individual farms, but due to a 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 increase the winter hardiness of certain species, it is recommended:
- Protect the root system from frost. This can be done using coniferous spruce branches, dry fallen leaves, peat, sawdust, industrial covering material. Foam plastic, which has high thermal insulation properties, has also proven itself well.
- Cover not only the roots, but also aerial part plants. Of course, it is difficult to protect the crown of powerful tree crops (although some gardeners manage to wrap lower part 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, which are 2-3 years old. Their root system not yet fully formed and is located close to the surface of the earth.