In northern China, the cold, dry and windy winter will cause some cold-tolerant tree species to suffer freezing injury or cause â€œphysiological droughtâ€ (also called freeze drought, cold drought or winter drought) from winter to early spring, causing the branches to dry up. If some branches are damaged, the whole plant will die. To ensure safe wintering of trees, you must understand the causes of cold hazards and take necessary measures.
The location and principle of low temperature hazard
(I) Root freezing damage is not due to natural hibernation in the root system, and its frost resistance is poor. The roots near the surface are vulnerable to freezing, especially in winter where there is little snow and arid sandy soil, and it is more susceptible to freezing. Frozen roots are often difficult to find in time. If the branch has sprouted in the spring, but after a while, a sudden death occurred, mostly due to freezing of the root system. Therefore, winter and spring seasons must do well overwinter protection work.
(b) Root-neck freezing injury began earlier due to the late growth of the root neck, and the cold-resistance was poor. At the same time close to the surface, the temperature change is large, so the neck is vulnerable to low temperature and greater temperature changes, so that the cortex is frozen (one side or the ring becomes brown and then dry or decay). Generally, earth can be used to prevent cold.
(III) Freezing of main stems and branches to prevent freezing of main stems. First, winter sunburn on the sunny side (especially in the southwest). Due to the large temperature difference in the early winter and early spring, the skin tissue moves with the increase of the sun-heating temperature, and the nighttime temperature drops rapidly and is frozen. The second is cracking (also known as longitudinal cracking, cracking). Due to the sudden drop in temperature in early winter, the cortex tissue rapidly shrinks, and the xylem produces stress and spreads the bark; ice in the intercellular space can also cause cracks.
Cold damage to the branches occurs mainly at the inward side of the birth. Cortical discoloration, necrosis, depression, or vertical dehiscence along the trunk, and some fluid flow occurred due to catheter rupture in the spring. The reason is due to the narrow annual rings at the delivery station, underdeveloped catheters, poor nutrition, low nutritional accumulation, and poor resistance to cold. At the same time, it is easy to catch snow at the delivery place, infiltrate the bark after the snow makes the tissue soft, and the sudden drop in temperature will be harmed. Common trunk package grass, tree hung grass and other methods to prevent cold. However, it should not be used in the city.
Currently used cold protection measures
(I) Frozen water In areas where winter soil tends to freeze, fill the ground with water once before the land is frozen. This is called "frozen water." The time for freezing the water should not be too early, otherwise it will affect the cold resistance. Generally, it is advisable to fill with water during the â€œday-to-night and night-freezingâ€ period so that after freezing, a permafrost layer will be formed around the roots of trees to maintain the temperature of the roots relatively stable and not to cause plant damage due to sudden changes in outside temperature.
(B) After the root-neck soil is frozen and water is combined, a soil pile with a diameter of 80 to 100 cm and a height of 40 to 50 cm is cultivated in the root and neck of the tree to prevent cold-frozen root neck and roots. It also reduces the evaporation of soil moisture.
(3) Covering soil Before the land is frozen, the soft and shrub-bearing trees can be overwhelmed and fixed with a layer of dry leaves (or no cover). Cover the soil with 40 to 50 cm and gently pat. This method can not only prevent freezing, but also maintain the humidity of branches and prevent tipping. Poor cold-resistant saplings and vines are used to prevent cold.
(4) The use of buckled baskets or buttoned pots may be used for the precious flowers and plants (such as peony, etc.) whose dwarf plants are relatively short. This method will not damage the original plant shape. In other words, the entire plant is buckled with large flower pots or baskets. Outside the soil or mud, leaving no gaps, to create a relatively warm, moist microclimate conditions to protect the winter plants.
(5) Wind barriers are used to mitigate cold and dry winds and cause damage to the trees. Wind barriers can be erected in the upwind direction of the trees. The materials used for the wind barriers are usually stalks of sorghum, bundles of corn stalks, hedgerows, or bamboo rakes and lushes. The height of the windbreak is higher than the height of the tree. Usually, the pine or bamboo poles are used to fasten the nails or the nails are tied with wooden piles to prevent the wind from falling down. The windbreaks are then covered with straw and tied with thin rods, or in the seats. External mud caulking.
Six white and white spray with lime plus lime sulfur on the white branches, can reduce the sun surface skin due to the large temperature difference between day and night damage, but also can kill some of the overwintering pests and diseases. For tree species whose flower buds germinate earlier, the tree body is sprayed white, and flowering can be delayed to avoid the danger of late frost.
(7) After spring irrigating in early spring, the land is thawed and water is supplied in a timely manner to keep the soil moist. This can reduce the soil temperature, delay flower buds sprouting and flowering, and avoid late frost damage. It can also prevent the spring breeze from blowing and make the branches dry.
(8) Cultivation of crescent-shaped earth mounds in the winter, where the soil is frozen, and in early spring, it is dry and windy in a continental climate region. Although some tree species are hardy, they are susceptible to freezing and drought and appear dead. Especially in early spring, the soil has not been defrosted, and the root system is difficult to absorb water, and the air is dry and windy, the temperature rises quickly, and the evaporation amount is large, often due to physiological drought. For this reason, the inconvenience of bending and burying the plants to prevent cold can be applied to the northern side of the trunk before the soil is frozen. A crescent-shaped mound with a height of 30 to 40 cm is curved southward. In the early spring, it can block the wind, reflect and accumulate heat to make the hole soil earlier and freeze, and the root system can absorb water and grow earlier, thus avoiding the occurrence of frost and drought.
(9) Rolling and Packing Grass For trees that are not tolerant to cold (especially newly planted trees), the trunks and some main branches must be covered with straw ropes or dried with straw to prevent the cold. When the grass is packaged, the grass is turned upwards, and begins to lay on the ground in half. From the dry base grass upwards, it is wrapped continuously. It is bundled every 10 to 15 centimeters horizontally and goes up to the branch point. If necessary, part of the main branch can be included. This method protects against the cold and should be removed after the night frost. It should not be delayed.
(10) Antifreeze and snowfall During or after the heavy snowfall, the snow on the branches should be promptly knocked out to avoid overstressing the snow and causing the branches to hang down, making it difficult to restore the original shape, or even to break or split. In particular, evergreen trees with dense foliage should be organized in a timely manner to hold snow, snow, and snow branches. For iced sticks, they must not be beaten, but they can be left unmoved. If they are too heavy, they can use lychee stays and remove them after they are frozen.
(11) Snowfall on the base of the tree The snow at the base of the tree can maintain a certain low temperature, avoiding the invasion of cold and strong winds. In the early spring, it can humidify and protect the earthworm, reduce the soil temperature, prevent buds from sprouting prematurely and be affected by the late frost. . In cold and dry areas, it is particularly necessary.
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