The first frost season is also called "frost"

The first frost is the last solar term in autumn, and the weather turns from cold to cold. The first frost generally appears in the middle and lower reaches of the Yellow River. This festival, the frost condenses the earth, the leaves are yellow, and the chill in late autumn is full. After autumn fruits and melons were harvested one after another, the growth of vegetation gradually slowed down or even stagnated, and it began to prepare for wintering, silently accumulating strength for the next year's germination.

The first frost is characterized by the first frost in the north. Although it is called "first frost", we have seen snow and it often rains, but no one has seen frost. Frost didn't fall from the sky. It is actually a white ice crystal condensed by water vapor in the air near the ground when the ground temperature drops below 0℃, which belongs to the phenomenon of gas condensation in physics. Frost and dew, snow and ice are all products of natural water in different climatic conditions, but frost is more dignified than dew, less cold than snow and ice, and has its own unique charm.

As for first frost, there are many poems that record or describe first frost in historical classics. "The Book of Songs, Wind and July" has a cloud: "Frost in September, washing fields in October; My friend drank and said that he would kill the lamb. " People are even more familiar with the phrase "White dew is frost, so-called Iraqis are on the water side" in The Book of Songs Qin Feng Sword. Cao Pi's Ge Yanxing has a description of "the autumn wind is bleak and the weather is cold, and the vegetation is like frost"; In the Tang Dynasty, Zhang Ji's "a night-mooring near maple bridge" and "Sleeping in the wind and fishing on a frosty night", Du Mu's "Walking on a Mountain" and Wen Tingyun's "Walking on a Good Day" all became famous sayings throughout the ages. These poems have both vivid descriptions and artistic conception. The scenery and breath of late autumn are perfectly integrated with the poet's feelings and imagination, and the scene blends with each other, which makes the seemingly cold image of frost have a little temperature.

Frost has a great influence on plant growth, and the phenological change of the first frost is also of great significance to guide agricultural activities. In the first frost season, the autumn harvest in most parts of the north has been swept away, and even the cold-resistant onions can't grow any longer, because "the first frost can't support onions, and the longer it grows, the more empty it becomes." "The first frost kills a hundred herbs", plants that have been hit by severe frost have no vitality at all. This is because the liquid in plants forms ice crystals due to frost, protein precipitates, and the water in cells extravasates, which makes the protoplasm seriously dehydrated and deteriorated. First, first frost harvested sweet potatoes and stored them in the cellar, which can be stored for a long time; However, the sweet potato harvested in the first frost is difficult to store and easy to deteriorate. Eggplant beaten by frost will wither, but radish after frost will become sweeter and crisper. This is because the sudden drop of temperature in first frost season will promote the decomposition of sugar in plants. At the same time, because the respiration of plants is weakened and the energy consumption is low, the decomposed sugar is not completely consumed, and the radish is sweeter at this time. It can be seen that frost is not only a signal that the weather is getting colder, but also an "inspector" of plant quality.

Frost protection of crops is very important. Although frost is closely related to frost, it is actually "freezing" rather than "frost" that really harms crops. Someone has done an experiment: put two leaves of a plant in a box with the same low temperature, one of which has frost and the other has no frost. In this way, the leaves that are not frosted are seriously damaged, while the frosted leaves have only slight damage marks. This shows that frost is not the main reason why frost harms crops. On the contrary, when water vapor condenses, it will release a lot of heat, which will turn heavy frost into light frost and light frost into dew, thus reducing freezing damage. Therefore, anti-frost is actually mainly anti-freezing and low temperature. At present, people usually use irrigation, mulching, smoking, fertilization and other methods to prevent crop freezing injury. From this perspective, it is better to say "frost kills a hundred herbs" than "the first frost kills a hundred herbs". "Frost" is the expression of cold weather, and "freezing" is actually the "enemy" that really harms crops.

Meteorologically, the first frost in autumn is generally called "first frost" or "first frost", and the last frost in spring is called "late frost" or "final frost". The period from the last frost to the first frost every year is a frost-free period, which is a season conducive to plant growth.

For thousands of years, the accumulation of life has given people more connotations to first frost: "wind knife and frost sword" shows the fierceness of first frost, "weather-beaten" is full of hardships of life, "adding insult to injury" makes first frost "worse" and "resisting snow" show unyielding spirit, but no matter how cruel others are, we should not "abandon ourselves to depravity".

In nature, in addition to the frost formed by water vapor condensation, some fruits will also frost. Just like the frost on the surface of grapes, it is actually a sugar alcohol substance secreted by itself, also called fruit powder, which is completely harmless to the human body. This is a sign that frost is still fresh grapes. On the surface of persimmon, it is usually covered with a thin and even layer of hoarfrost, which is the sugar condensate precipitated with the evaporation of water when the pulp is dry. Known as "persimmon cream", it contains mannitol, glucose, fructose, sucrose and other ingredients, and can be used as medicine. "Persimmon cream" dries the whole persimmon. After processed and boiled, persimmon can be used to treat hematochezia and cough in the elderly, and it also has a certain effect on hepatitis. Persimmon cream is the essence of persimmon. Now many cosmetics and skin care products are also named after "cream". Although they are mostly chemical compounds or extracts, they are not as cold as natural cream. They dress up their faces, beautify their lives and make "cream" more lively and warm.