The advent of the global warming era worries almost everyone. But for gardeners it is much more important to understand what winter hardiness is, how important it is for plants. Debunk some myths about this phenomenon.
Plants can die because of severe frost.
Directly frost, that is, low temperature, does not cause suffering to plants. But frost creates ice crystals in the tissues of plants, which damages living cells. Also very important mode of thawing. For a hardened plant, deep freezing is also not a problem, if cooling takes place under conditions of slow formation of ice, and thawing will also be slow. In the laboratory in the mid-20th century, Russian scientists were able to freeze the shoots of black currant to -253 degrees, in the future the experimental plants developed as if nothing had happened, successfully blossomed. In this case it should be taken into account that the experimental varieties – Lakston and Leah are not very fertile at all.
Winter hardiness determines the temperature in degrees, which the plant can withstand without losses.
Many believe that if the frost occurred at -30 degrees, and the fruit trees did not suffer, it means their winter hardiness is -30 degrees. However, for the ability of plants to withstand low temperatures there is a special term – frost resistance. The term of winter hardiness is quite wide, it includes the ability of a plant to bear the whole spectrum of winter burdens – it’s the notorious frosty frosts, and sharp thaws, significant differences from heat to cold and so on.
All plants are monolithic in terms of frost resistance – all parts stand or pass before the same temperature.
This is not true, it is noted that in the same plant different parts can react differently to frosts. In fruit trees the most unprotected part is the roots, usually for them the temperature in 9-10 degrees of frost becomes critical, but this indicator depends on the culture and the stock. In fruit plants the kidneys are always more tender than in growth plants, the wood freezes more often than the bark.
Winter hardiness of a plant depends only on itself.
Undoubtedly, the genes of the bush or tree have already laid their ability to endure winter with attendant problems, but no less important is the current state of the plant, its health, living conditions in a particular year. The maximum winter hardiness accompanies well-groomed and strong plant, but weakened from diseases, abundant harvest or poor-quality food, or other problems, the plant may have a lower winter hardiness.
Throughout the winter, the hardiness of the bush or tree does not change.
During the autumn the plant passes through a kind of hardening, during it the frost resistance increases. In a state of deep peace, winter hardiness continues to increase. Approximately by the end of December, for most plants in the middle belt, deep peace ends, at this time the maximum winter hardiness. In the future, resistance to frost begins to fall, and it does not even depend on the weather, each thaw only strengthens this phenomenon. Has the influence and duration of the thaw, the longer it is longer and warmer, the faster the frost resistance falls. However, one should not think that this process is irreversible, in part, stability can intensify, especially in cases when frost comes gradually, and not abruptly. So do not be surprised if the tree in the beginning of December will suffer a frost of 35 degrees, and in early March will suffer from a thirty-degree cold. Yes, and an unexpected frost of 5-6 degrees in March can cause blackening of blossoming leaves.
In the fruit trees, the lower parts of the trunks are cold.
It is in these places after the end of the winter that the parts of the dead bark are found. In such damages, the main cause of damage is not frost, but temperature drops in the early spring. In the daytime, the sun heats the bark areas, which are already losing their winter hardening, starting the “spring” mode of operation.And at night the temperature drops significantly and those parts of the cortex that hurried to enter the spring may be damaged. That’s why it is recommended to whiten the trunks at the end of winter, and not in the spring, which is incomprehensible for many.
In the period from the end of the fall leaf to the beginning of bud blossoming, a deep sleep of garden plants occurs.
It is believed that during this period there are no changes, but if you transfer the twigs to the heat, they immediately begin to blossom. The reality is much more complicated. After the leaf fall, the plants fall into a state of deep sleep, rest. Such a period is vital for plants, no heat can awaken them and interrupt this process. Gradually, a deep peace is replaced by a forced rest. This means that such a pause is not vital for plants, but this remains the only way to survive the coming frosts. At this stage, the kidneys are able to begin to dissolve with the onset of heat. For the external observer, both states look the same – the plant looks lifeless, but it develops, so the buds begin to form future inflorescences.
Winter frosts are much more dangerous for buds, than for ovaries, which tolerate the cold better.
Frost resistance of plants begins to decline in the middle of winter, continuing during the spring. That is why the ovaries are always more tender than flowers, which can be damaged by frost more strongly than buds. It is for this reason that the unfolding leaves can freeze more than the kidneys that have recently burst.
Climatic zones for cold resistance of plants indicated in foreign sources have no relation and benefit for Russian gardeners.
The very subdivision of plants according to their suitability for different climate zones was actually proposed in the USA, in the Agricultural Department. But in Russia it is also possible to focus on this approach, because there are several climatic zones on our territory. The zones are located with the help of indications of the lowest possible temperatures, which are fixed in these areas. The first zone is considered to be the coldest zone, it can have frosts below 45 degrees, the warmest is the tenth zone, according to the classification in its territory, the temperature does not fall below 1-4 degrees above zero. On the basis of this classification, for example, plants for the fifth zone or lower are recommended for the middle zone of Russia.
According to the plant’s belonging to the climatic zone, its winter hardiness can be unambiguously determined.
Only one correct number can not guarantee the plant a happy life on this site. The matter is that it is not necessary to consider, that winter difficulties are only frosts. Each site has its own nuances that affect the condition of plants – it’s microclimate, soil, moisture, duration of daylight. These parameters, which are very important for plants, are not reflected in any way by the number of the zone, since they are individual for the terrain. Yes, and not excluded the extreme temperature difference, which are of record or anti-record nature. However, a reverse example is also possible, so some delicate plants (grapes or roses) can successfully winter in rather cold zones with the help of special shelters. Therefore, the band method provides only general concepts of winter hardiness of plants.