Apple trees of dessert varieties popular on the market are mostly not frost-resistant. Recent sharp temperature changes during thaws and severe frosts have significantly damaged orchards and fruit nurseries in the middle climate zone.
Since cold air accumulates in the lower part of the slope, near dense forest belts and buildings, to avoid damage to fruit trees by low winter temperatures and spring frosts, the garden should be laid out in an area where such problems do not exist, although it is not easy to find such a site in the horticultural region.
HARDENING OF TREES
With the end of growth, shorter days, and the onset of low temperatures, trees harden and enter the phase of winter dormancy. Hardening conditions can be improved by appropriate agricultural measures.
Excessive nitrogen fertilization should be avoided, as it impairs the ability to harden by “delayed” growth of seedlings in the nursery or trees in a young garden and threatens to freeze even in moderately cold winters.
Hardening is accompanied by water loss and accumulation of sugars and specific protein compounds, acquisition of a fiber-mesh structure by cells and higher permeability of cell walls and cytoplasm. As a result, tissues become resistant to freezing at temperatures several tens of degrees below zero and are not damaged by ice crystals. With a slow decrease in temperature, hardened plants can withstand severe frosts, but sudden cold after a warm autumn is very harmful to them.
In a nursery, it is risky to keep dug seedlings with insufficiently lignified shoots in an unprotected pinning in the open ground; it is better to store them in a refrigerator at a temperature slightly below 0°C and the highest possible humidity. Purchased seedlings can be stored under cover, sprinkling the roots with wet sand, fresh sawdust or soil, placing poisoned mouse baits nearby, and systematically monitoring the condition of the plants.
In order to protect rootstocks and budding eyes from winter damage and to retain snow in the seedling school, rye or mustard is sometimes sown in the fall, which, if necessary, is destroyed with a contact herbicide in early spring.
TREATMENT OF DAMAGE
February thaws with sunny warm days and the return of cold weather cause a lot of losses. In February, when the air temperature is below 10°C, the bark of trees on the sunny side can heat up to +50°C, which causes the bole to burn and crack. In the past, this was prevented by whitewashing, but in modern orchards with dense tree planting, this requires appropriate costs.
PROTECTION AGAINST FROST
In the United States, heating with coal and peat briquettes, paraffin candles, diesel fuel, and gas has been practiced for more than a hundred years to protect citrus, and less commonly peach and apple trees from frost. The heat sources are placed according to the 6×6 or 7×7 m (204-277 pieces/ha) scheme, maintaining a sufficiently strong constant and regular heating with the consumption of a considerable amount of combustible materials until the frost stops, and the gas burner system sometimes turns on automatically.