Mineral Review

How to determine whether a tree is frozen or not?

During severe frosts, the branches of fruit trees freeze slightly. You don’t have to wait until spring to assess the extent of the damage. The diagnosis can be made already in winter, this will help determine the timing of spring pruning, as well as think about ways to resuscitate the garden. Checking freezing of apple tree buds

What kind of frost is dangerous for fruit trees?

Different fruit crops differ significantly in their winter hardiness. Semi-cultivated apple trees are least afraid of frost. Stone fruits: apricots, cherries, as well as plums and cherries are more defenseless against cold weather. Resistance to freezing at low temperatures is determined at the genetic level, so different varieties of fruit and berry crops differ significantly in frost resistance. When purchasing seedlings, it is necessary to clarify which rootstock the variety is grafted onto; not only the height of the tree and the speed at which it begins to bear fruit depend on this, but also the frost resistance of the root system. Thus, the common dwarf rootstock M9 is characterized by low frost resistance. For the Moscow region, the middle zone and regions with harsh winters, it is better to give preference to varieties grafted onto dwarf rootstocks B9, P60 or onto medium-sized rootstock 57-545, When choosing seedlings, you should give preference to local nurseries that grow zoned varieties. When planting southern varieties in regions with cold winters, there is a high probability of significant or complete freezing of the seedlings. So, apple tree varieties “Melba” и “Sinap Orlovsky” withstands down to -29°C, “Cinnamon Striped” и “Zhigulevskoe” – up to -34°С, and “Grushovka Moskovskaya” — up to -45°С. Severe frosts at the beginning of winter are not as bad for the garden as a sharp cold snap in February or temperature swings in March. In November-December, trees are in a state of deep dormancy, so they can withstand even extreme cold without damage. Apple tree bark at the end of winter In February, plants are already beginning to emerge from hibernation. The sun is shining brightly like spring, and on a fine day the temperature on the thermometer creeps up. The dark bark heats up in the sun, and the tree awakens, juices begin to circulate in its tissues. And at this moment, a sharp cold snap causes significant harm. Frostbites on an apple tree The liquid in the tissues of the tree freezes and increases in volume, which leads to ruptures in the bark – frost holes. Long cracks run vertically along the skeletal branches and trunk. If left unattended, the bark will peel off and the wood will die.

What factors influence frost resistance?

The age and condition of the tree affect its winter hardiness. The most vulnerable are seedlings that were planted in the current year: in spring or autumn. They have not yet had time to take root properly, so deep freezing of the soil can lead to the death of the root system, and consequently the entire tree. Young trees that produced their first harvest this year are also at risk. They spent a lot of effort on the formation of fruits, so they did not have time to properly prepare for winter. After the first “signal” harvest, cherries and apricots often freeze out. Stone fruits are more vulnerable to severe frosts than pome fruits: apple, pear, quince. Sweet cherries, apricots, southern varieties of plums and cherries are often frozen to the level of the snow cover. Old trees, which have served faithfully for many years, at some point “get tired”. After a particularly abundant harvest, they do not have time to regain their strength and go into winter weakened, which can lead to partial freezing of the skeletal branches. A bountiful harvest, attacks by insect pests, and fungal diseases worsen the winter hardiness of trees. If in the second half of summer gardeners stop fighting aphids, the pest sucks the juices out of the young shoots, which is why they do not have time to ripen before the cold weather and freeze in the winter. Excess nitrogen fertilizing in the second half of summer leads to rapid vegetative growth. Fattening shoots are most likely doomed to freeze. Foliar fertilizing with silicon, on the contrary, improves the frost resistance of trees. Fertilizers such as “Siliplant” or “Silicon in chelated form” will help plants survive the winter without damage. Root feeding with potassium or potassium-phosphorus fertilizers in August-September helps the plant prepare for winter. Potassium stimulates the outflow of nutrients accumulated in the leaves into the bark and wood. Due to the increase in sugar content, the cell sap becomes thicker and its freezing point is much lower. Water-recharging irrigation carried out several days before the first frost has a beneficial effect on the wintering of fruit trees. Wet soil retains heat longer. Water is a good conductor – heat rises from the depths to the surface through soil capillaries.

Signs of freezing

Freezing can be light, partial or complete. Depending on the severity of the damage, the tree may recover next season or continue to grow by awakening dormant buds on the living part. If there is severe freezing, the orchard has to be uprooted and a new one planted, from varieties with higher frost resistance. In the cold, wood becomes brittle, so branches break easily, but this is not a sign that the trees are frozen. We will get a complete picture of the damage only in the spring, in April-May, when sap flow begins, flowers bloom and the first leaves appear. You need to understand that after partial freezing, the tree will take longer to come out of dormancy than usual, so do not rush to pick up a pruner or saw – the branches may still turn green. If the aboveground part of a young seedling has frozen above the level of snowdrifts, the tree still has a chance. After pruning the damaged part, growth will continue due to the formation of new shoots from dormant buds. If the tree freezes to the grafting level, then it will degenerate into a wild one – new shoots will come from the rootstock, and then the gardener will have to get rid of the useless seedling or re-graft it. Sometimes the tree blooms joyfully and produces young leaves, and the gardener already breathes a sigh of relief, but that was not the case. The leaves wither, the flowers fall off – these are sad signs that the frost has damaged the roots. The plant has used up the reserves of nutrients accumulated in the wood to flower, but it cannot live without roots.

Wood

Frost may damage the wood slightly, and the tree will then recover over the next season. Frozen wood changes color – from white-green it becomes gray-green or beige. Experienced gardeners use a trained eye to determine the shades of wood color. To improve understanding, it is better to have a “fulcrum” in the form of a healthy branch that has not been frozen; its cut is taken as a sample. The more the wood is frozen, the darker its shade will be: for apple, quince and stone fruit – from brown to dark brown, for pear – to almost black.

Cambium

Much more dangerous is the freezing of the cambium. It can withstand lower temperatures than wood. The thinnest layer of cells, which is located between the bark and the pith, is the basis for the growth of the tree. It is due to the division of cambium cells that the shoots, skeletal branches and trunk thicken. Even if the wood is severely frozen, but the cambium is not damaged, the tree will be able to recover. With minor damage, frostbitten wood gradually becomes lighter, but with severe damage, it remains dark; such branches subsequently become fragile and vulnerable to bending.

Flower buds

Flower buds have lower frost resistance than vegetative ones. When the generative buds freeze, the trees bloom, but the fruits are not set because the pistil is damaged. With severe freezing, flower buds do not bloom at all or dry out after partial bloom.

How to determine if a tree is frozen

Sanitary pruning of the orchard is carried out in early spring, before the sap begins to flow. However, this rule only works for trees that have wintered well. If the plants are frozen, you need to skip the early stages of pruning and wait until the flowers and leaves bloom, only then will the extent of the damage become clear. To understand when to pick up the pruning shears and garden saw, in winter it is necessary to determine how the garden withstood the frosts. For testing, a few branches from each tree are enough. To determine the condition of the branches, two-year-old shoots more than 1 cm thick and 30-40 cm long are used. In adult trees, they are cut from the central part of the crown, from the four cardinal directions. In order to further understand which side of the plant is more frozen, the samples are marked. In young trees with a small crown, 1-2 branches are cut off for testing. It is important to understand that the nature of the damage does not appear immediately, but over several days, from 5-7 days to 3 weeks. First, you need to ensure smooth thawing of the cut branches. Samples cannot be taken home immediately – from cold to warm. In order for the branches to gradually thaw and warm up, they are left for a day or two in a room with a minimum positive temperature: on the terrace, in the cellar, or placed in the refrigerator. Thawed branches are transferred to a warm place and left until completely warmed or until they grow back. The process is most effective at a temperature of +20°C; at lower temperatures the results are not always obvious. It is important to maintain high air humidity so that the branches do not dry out.

Slice testing

The easiest way to assess damage is to test from a fresh cut. After slow thawing, for further warming, the branches are buried in damp sawdust or wrapped in damp sphagnum moss and kept warm at +18-22°C for 3-5 days. Twigs for testing To determine the test results, an oblique cut is made in the middle part of each shoot. Assess the shade of the wood, paying special attention to the condition of the cambium. Healthy wood should be light-colored, the cambium layer should be green.

Growing

This method takes more time, but also gives a more reliable result. When conducting a scientific analysis of damage, the regrowth of shoots is carried out within 20-60 days; amateur gardeners usually limit themselves to one to two weeks. The shoots must be placed in a container with water (the water layer is no more than 5-7 cm, it should cover only the lower part of the branches). To maintain high air humidity, put a plastic bag on the container, which is opened slightly every day and sprayed from the inside with water. Growing shoots Before growing, it is necessary to refresh the cuts. The tips of the shoots are trimmed in water to prevent clogging of blood vessels, which occurs when pruning in air. The cut is made with a sharp knife at an angle of 45°. The container with the growing shoots is kept warm. At temperatures below +15° the shoots may turn sour, which distorts the results. After 1-2 weeks, the condition of the buds is assessed by their swelling, and the wood in the middle part of the shoots is cut, as in the previous experiment. To determine the condition of flower buds, they are examined separately. The swollen buds are separated from the shoots, cut lengthwise with a straight razor or scalpel and examined under a magnifying glass. A healthy kidney has green tissue, while frostbitten buds have a brown or dark brown color at the base and central part.

Assessment by water condition

Even in the process of growing branches, you can draw the first conclusions about the state of the water in which the shoots stand. If the branches are not viable, after 2-3 days the water turns sour and turns yellow and brown. If the branches are alive, the water remains clear for a long time, and the buds swell on the shoots themselves.

Assessment of the condition of skeletal branches and trunk

In the spring, after the snow has melted, you can determine the condition of the tree’s skeleton: the trunk and main branches. Longitudinal cracks on skeletal branches are signs of frost damage. If freezing occurred at the beginning of winter, by spring the bark will begin to peel off. To determine the condition of the trunk, it is necessary to examine the bark; it must be intact, without spots or darkening. It is acceptable to make several vertical cuts to assess the condition of the cambium.

What to do if the tree is frozen

Experienced gardeners say that you should never give up. Even after harsh winters, when orchards freeze heavily, life goes on – trees can be revived by sanitary pruning, the formation of a new crown, or re-grafting. Only the death of the root system is final and irrevocable. If the trees did not survive the winter well, do not rush with spring pruning. Give the garden time to warm up and “come to its senses.” Frostbitten branches will never wake up, and then it will become clear how to carry out sanitary pruning. After a particularly harsh winter, pruning must be done in two stages. At the end of May, some branches stop developing. Leaves remain small, deformed or dry out completely. Such branches will also have to be cut back to healthy tissue. All dead branches will need to be removed; dead wood has no place on a living tree. Pathogenic fungi and wood-boring insects quickly recognize that an object for disposal has appeared and attack the plant. Since pruning will be carried out after the start of sap flow, it will be necessary to handle the cuts especially carefully to avoid infection. When moving from tree to tree, the pruning shears and garden saw must be disinfected with alcohol or a preparation “Agroyod”, this will help avoid the spread of viral diseases, if any. Fresh sections must be disinfected with a 1% solution copper or iron sulfate (100 g per 10 l). After drying, the sections are covered with garden varnish. “Zhivinka”. Frost holes on skeletal branches also need to be disinfected and covered with garden varnish. If the bark has already begun to peel off, it is first stripped down to healthy tissue, and only after that the wound is disinfected and covered. You need to work with a sharp tool so as not to crush the wood tissue, but to cut it off, this speeds up the healing process. The gardener needs to understand that heavy pruning will lead to the growth of a large number of tops at the cut site. They will thicken the crown, which will lead to poor air circulation and the spread of fungal diseases. Some of the tops need to be cut into rings in the summer. The strongest and most well-placed shoots are left to replace lost branches. Top shoots are distinguished by their strong growth, large leaves and tendency to grow vertically. To turn a vegetative shoot into a fruiting branch, the tops are gradually pulled back until they are at an angle of 45-60°C and secured in this position. In young trees, the crown of which has completely frozen to the snow level, it is necessary to form a new trunk from a young shoot. In the first year, you need to give it support so that it does not break off from the trunk in strong winds. If a replacement shoot growing from a dormant bud is fixed vertically, after a couple of years it will not be noticeable that the tree was ever damaged. The formation of vigorous basal growth and the absence of any life on the trunk above the grafting site indicates that the cultivated part of the tree has died. If the gardener does not want to try his hand at grafting, he will have to uproot this seedling. When planting a new garden, the gardener needs to analyze the mistakes made. Even within the same garden plot, the microclimate varies in different parts of it. In one place, plants suffer more due to strong winds, in another – due to the abundance of snow or stagnant melt water. It may be necessary to find another, more favorable location for new seedlings. At the base of the tree, in the area of ​​the root collar, when peeling off the bark, you may notice that the layer of tissue underneath is unnaturally darkened. If the leaves are pale and misshapen, this may also be a sign of frostbite, although it can often be confused with illness. Frozen flower buds and leaves turn black and fall off over time.
The degree of damage can be determined by the nature of the changes and the strength of the wood’s coloring. A light brown color indicates light frost, and the darker the brown color, the stronger the frost resistance of the fruit. In case of very severe damage, the bark immediately falls off. During prolonged cold weather, longitudinal cracks may be observed along the tree trunk, which arise due to the formation of ice crystals at the cellular level. In young trees, watch for annual branches, and in adults, for fruit buds and older, 3-4-year-old branches. In early spring, it will be possible to collect any fruit buds and make a diagnosis. Use a sharp knife to make a cross cut across the buds. The central part of damaged buds is dark brown. Inspect the wood and the core of the shoots.

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