How Do The 24 Solar Terms Affect Tea Production?

The Big Dipper and the four Seasons 

You may have heard about 24 Solar Terms (system) before, but you may not be sure what they are or how they come into being. Ancient farmers in China invented the 24 Solar Terms by constantly observing the movement of celestial bodies such as the sun and moon.

Records about solar terms on oracle bone inscriptions

However, among countless stars, the Big Dipper seems to attract the most attention of ancient agriculturists and astronomers in China. They believed that the Big Dipper was an important constellation in the Northern Hemisphere. It is so important that people at that time named every star of it:  Tianshu, Tianxuan, Tianji, Tianquan, Yuheng, Kaiyang and Yaoguang. Because the seven stars that make up the Big Dipper are arranged in a shape like a ancient measuring container "Dou" in China, it is named "Bei Dou Qi Xing (North Dou Seven Stars)" by China people. The upper three of the Big Dipper is called (鬥柄 [dǒubǐng]) handle of the Dou. The Big Dipper appears in different parts of the northern hemisphere with the change of time. It cyclically rotates - the handle of the Dou rotates clockwise for a cycle. The time it takes to make a full revolution is called one "歲(sui) / year" . So the ancients could decide the season according to the direction pointed by the handle: when the handle points to the east, it means that spring is coming; When it points to the south, it means that summer is coming. Similarly, it's autumn in the west, and winter in the north.

Ancient Chinese calendar and 24 solar terms

As early as the Spring and Autumn Period (770–476 BC), Chinese ancestors had already established two major Solar Terms, ri nan zhi (日南至 'Sun South Most',sun moves to the southernmost point ) and ri bei zhi (日北至 'Sun North Most',sun moves to the northernmost point ). Later, the ancients divided a year into 24 equal parts according to the relative position of the sun and the moon, the changing law of the weather and growth trend of animals and plants, and gave each equal part a proper name. This is the origin of the 24 solar Terms. 

Measuring the shadow by Duke Zhou

Zhou Gong (Duke Zhou) was not only a famous politician and strategist in the early Western Zhou Dynasty, but also had great achievements in astronomy and geography.

Gui Biao -an ancient Chinese sundial. It consists of a long and thin dial (Gui) and one post (Biao), which are used to measure the length of a year and 24 Solar Terms.

As early as the 20th century BC, people in the central plains of China began to measure the length of the sun shadow using the "Gui Biao" method to determine the season.

Gui biao

"Gui Biao" is a tool to measure the length of sun shadow. As we all know, China lies in the northern hemisphere. At the Winter Solstice, the Sun reaches the highest position in the southern  hemisphere sky. The Sun in the sky is farthest south in the Northern Hemisphere (December 21 or 22), and on that day China therefore  has the least daylight and the longest night and the shadow in the northern hemisphere is the longest, and vice versa. Therefore, the ancestors of chinese people could determine the winter solstice and summer solstice by repeatedly observing and recording the position of the longest and shortest shadow cast on the "Biao" at noon. Winter solstice has the longest shadow, and the adjacent days change obviously, so "Biao" is more conducive to determining the winter solstice. The structure of "Gui Biao" is very simple, mainly consisting of a long thin dial called "Gui" and one or two poles called "Biao". According to the record, the "Biao" made by Zhou people is about 185 cm high. In the sun, the shadow of the "Biao" will fall on the surface of "Gui", and the length of the shadow will change with the passage of time caused by earth's rotation. When the "shadow" reaches its maximum length of 450 cm, this day is designated as the "Winter Solstice", while when the "shadow" is only 35 cm long, this day is named "Summer Solstice".

The rotation of the Big Dipper and seasonal changes

In the late Warring States period, the twenty-four Solar Terms had further developed. Historians found in Mister Lv's Spring and Autumn Annals , a book written in the late Warring States period (475–221 BC), that the eight most important terms marking the four-season transitions, namely, Start of Spring, Vernal Equinox, Start of Summer, Summer Solstice, Start of Autumn, Autumnal Equinox, Start of Winter and Winter Solstice, have been established based on the continuous observation of  the sun, the moon and natural phenomena. At last, the complete 24 Solar Terms came into being during the Western Han Dynasty (206 BC-24 AD). In 104 BC, 24 Solar Terms were first used in Taichu calendar (as a supplementary calendar for guiding farming) which appeared 58 years earlier than the Roman Julian calendar. 

The current system of 24 Solar Terms comes from the method of dividing the ecliptic more than 300 years ago. The annual trajectory of the sun is divided into 24 equal parts, each 15° is an equal part, and every 1 equal part is a solar term, starting from the Beginning of Spring, ending with Major Cold. This division may not seem very scientific, because the sun's annual apparent motion is not uniform, that is, it moves at different degrees in the ecliptic during each solar term. Liu Zhuo, an astronomer in the Sui Dynasty, put forward a new division method in 1645, that is, to determine the specific length of Solar Terms according to the length of the time interval that the sun takes to travel the same degree. At that time and even today, this division is of great significance, and it has a far-reaching impact on China and even East Asia.

The 24 Solar Terms scientifically reveal the law of astronomical and meteorological changes in a year and it skillfully combines astronomy, farming, phenology and folk customs. It not only plays a guiding role in agricultural production, but also influences the ancient people's food, clothing, housing and transportation, and even the formation of cultural concepts.

A brief introduction to 24 Solar Terms. 

The 24 solar terms and twelve zodiac signs

 In the past, the main challenge faced by agricultural production was the unpredictable weather. The 24 solar terms originated in ancient times to help people better understand climate/weather change, so as to avoid natural disasters and make better use of natural resources to improve their living standards.

Seasons and Solar Terms 

The eight Solar Terms of the 24 Solar Terms are used to explain the changing sequence of the four seasons in a year are:

Spring Equinox, Autumn Equinox, Summer Solstice, Winter Solstice, Beginning Of Spring, Beginning Of Summer, Beginning Of Autumn And Beginning Of Winter.

Among them, Start of Spring, Start of summer, Start of autumn and Start of winter indicate the beginning of the four seasons, which applies to the whole of China. In modern climatology, four seasons are divided according to the average temperature of the pentad (five days are one pentad), that is, the period with the average temperature of the pentad is lower than 10℃ is called winter, and the period when the average temperature of the pentad is higher than 22℃ is called summer, with spring and autumn in the middle.

According to this standard, the time of dividing the four seasons in the tea region of Zhejiang is inconsistent with that of the Solar Terms, with a general difference of more than 20 days. This difference is very small in summer, but big in autumn. 

Twenty-four solar terms

Twenty-four solar terms

Among the 24 Solar Terms, there are five Solar Terms reflecting the change of temperature: Minor Cold, Major Cold, Minor Heat, Major Heat and End of Heat. White dew, Cold dew and Frost's Descent seem to describe the condensation of water vapor, but actually they also reflect the process and degree of temperature drop. Minor cold and Major Cold occur in January in the Gregorian calendar, indicating the coldest period of the year. Major Cold is colder than minor Cold in degree. 

Precipitation and Solar Terms  

Precipitation is reflected in Rain Water,Grain Rain, Minor Snow ,Major Snow. So Rain Water basically means that the amount of rain is beginning to increase. Grain rain falls around April 21. During this period, the Yellow River basin is in a dry season with little rain. Therefore, the rain at this time is very beneficial to crops, so it is called Grain Rain. 

Phenology and Solar Terms 

In the Solar Terms, there are four Solar Terms reflecting phenological phenomena, i.e., Awakening of Insects, Qingming (Clear and Bright ), Small Full (Grain) and Grain in Ear .

"Awakening of Insects" is in early March, indicating that the temperature gradually rises, thunderstorms begin to appear, and hibernating insects and animals begin to move. 

Qingming (Clear and Bright) falls on April 6. Along the Yellow River Basin, the average daily temperature rose to 12 to 14 degrees Celsius. At this time, the climate is warm and plants are flourishing. The dull, cold and yellow scenery of winter has been replaced by vibrant green, so it is called Qingming (Clear and Bright ) 

Small Full (Grain) is on May 21, it means that the seeds of barley and wheat are beginning to swell, but they are not yet fully ripe.

Grain in Ear on June 6 refers to the time when awn crops such as barley and wheat are about to be harvested or millet sowed. 

Tea making and Solar Terms 

Although the 24 solar Terms was created by the ancient people in China, the 24 solar Terms is now regarded as an important part of China culture.

China has a long history of planting tea, and the 24 solar terms have played a great role in tea planting.Located in the Jiangnan (South of the Yangtze river) tea region (one of four tea producing areas), Zhejiang province is famous in China for its high-quality green teas, such as Longjing.Next, based on historical data and production experience, I will introduce to you the influence of the twenty-four solar terms on tea planting in Zhejiang.

 China's ancient economic and cultural center was located in the Yellow River valley.The natural phenomena reflected by the 24 Solar Terms are very close to the climatic characteristics of the middle and lower reaches of the Yellow River Basin.However, many solar Terms are also applicable to Zhejiang and other provinces in the middle and lower reaches of the Yangtze River. 

The role of 24 Solar Terms in tea production 

The most basic requirement of agricultural production is to pay close attention to seasonal changes and master the climatic characteristics of each season. Therefore, we can say that the ancient tea production was highly dependent on the twenty-four solar Terms.

In order to obtain high-quality tea and increase output, tea farmers in China have created many agricultural proverbs to arrange tea production activities such as sowing, picking and management of tea gardens.

Mingqian tea

The 24 solar terms were used to guide the proper time of tea planting and transplantation 

The time of planting and transplanting tea trees is very important. Picking appropriate planting time can improve germination rate and let tea plants grow well.Here are a few examples of Solar Terms-related proof:

"春前播種早，春後播種遲，雨水驚蟄最適宜。" 

For planting tea, time is too early before the beginning of spring, and it is too late after the vernal equinox. The in-between ("Rain Water" and "Awakening of Insects" ) Solar Terms are most suitable.

"雨水種茶用手捺，春分種茶用腳踏，清明種茶用鋤夯也夯不活。 "

During the "rain" solar term, it is easy to grow tea with bare hands. During the vernal equinox, tea trees need to be steadily planted on the steps to survive. If teas are planted during or after the Qingming Festival, they will not survive even if you carefully take care of them with a hoe.

Use 24 Solar Terms to guide tea garden management 

The key to increasing output and improving tea quality is garden management. Some examples of tea management proverbs related to the 24 Solar Terms are：

"驚蟄前挖金，春分後挖銀"

Digging gold  before Awakening of Insects,  digging silver after  Spring Equinox 

"小寒大寒茶要凍，人要戴帽穿棉襖，茶園立冬要鋪草 "

Scarifying or weeding should be done before tea buds sprout, otherwise it will do harm to tea growth.

The tea region of  Zhejiang  is the coldest during Minor cold and Major Cold. In some areas, the lowest extreme temperature is lower than -6℃, or even -12℃. Tea trees are vulnerable to freezing. In any case, low temperatures should be avoided, as low temperature can lead to a loss. Therefore, in order to prevent the tea tree from freezing, it is necessary to cover tree crowns with straw, weeds, etc. or spread grass on the root of the tea tree before Winter Solstice (just as people need cotton coats and thick hats in winter). 

Tea tree seedlings

Use 24 Solar Terms to guide tea picking 

The timing of picking tea is critical. Because it is not only directly related to the output, quality and farmers' income, but also affects the next year's harvest. Agricultural proverbs about tea picking in Zhejiang tea-producing areas include.

The tea picked before and after Qingming is as precious as treasure, while the tea picked in long summer is as worthless as grass, and the tea picked before and after Grain Rain is just in the right balance.

In general, the tea buds picked in Zhejing tea area around Qingming (Clear and Bright) can be used to make high-quality tea, such as the world-famous super longjing tea is picked before and after Qingming (Clear and Bright), so the agricultural proverb says that the tea made during this period is precious as "treasure" or "tribute", but for ordinary tea, it's too early to pick. Before and after Grain Rain, tea buds have expanded to three or four leaves, the yield has increased, and the quality is good.

When it comes to Start of Summer or Small Full (Grain), the tea is coarse and old, the quality is barely satisfactory, and it becomes "weed" and worthless.

Wrap up 

There is no doubt that the twenty-four solar Terms are crucial for the prosperity of ancient agriculture in China.  Although the twenty-four solar Terms are the product of ancient agricultural civilization, they are widely known in today's China.  Because of its scientific basis, it is indispensable not only in agricultural production but also in China people's daily life.  There are many famous teas produced in China according to solar Terms.  In the next article, I will continue to introduce you to the relevant knowledge.