Why are there many locust trees in old Beijing?

In fact, Sophora japonica is widely eaten in northern China. According to records, Chang 'an in the Tang Dynasty, Nanjing in the Eastern Jin Dynasty and Luoyang in the Northern Wei Dynasty all used Sophora japonica as street trees. Among them, there is a humanistic complex. First of all, the ancients thought that Sophora japonica was a gentleman's wind, upright and tough, with a wide shadow; Second, Sophora japonica is a symbol of good politics. Three Sophora japonica trees were planted outside the courtyard in the Zhou Dynasty. When the three courtiers met the emperor and dealt with people's grievances, they all stood under the tree. Therefore, people widely plant Sophora japonica to show respect for staying up late. Of course, the key to the promotion of Sophora japonica lies in its species advantage. Sophora japonica has a good life, acid and alkali resistance and low growth requirements. Its branches are very straight, and it is not easy to fall down in heavy rain and strong wind, so it is suitable for planting in cities. In the Tang Dynasty, trees were not allowed to be planted on the roadside of Chang 'an for security reasons. However, with the increase of urban population, the use of firewood has become a problem for residents, so they have to encourage tree planting. Sophora japonica is a mainstream tree species because of its fast growth period, easy paid logging, few lateral branches and no obstruction of sight. Sophora japonica has a close relationship with the Tang Dynasty. In the Tang Dynasty, there were cakes of Sophora japonica leaves, which were cold washed. Cold scouring is today's cold noodles. When making noodles, add the juice of Sophora leaves, which is the most beautiful. Sophora japonica leaves are bitter and toxic, but they can remove fire and have anti-inflammatory effects. It can be seen that people had a deep understanding of Sophora japonica by transforming it into food at that time. Old Beijing loves Huai because it is an immigrant city. Ming Chengzu moved to the capital and immigrated to Shanshan. Hongtong County is a big transit station, so there is a saying "Ask me where my hometown is, there is a big locust tree in Hongdong, Shanxi". In ancient rural areas, the management was loose, and the people communicated by "establishing a society", that is, two "society days" every year, where everyone got together and celebrated by drinking. The club is presided over by the old man. Usually, when they have something to do, they will step in. Old Beijingers call Sophora japonica their hometown, so they naturally plant Sophora japonica widely after taking root. In the Ming and Qing Dynasties, the number of locust trees in Beijing surged and became a city card. However, Sophora japonica is prone to insects, that is, the inchworm commonly known as "eating goods", which is disgusting. The word Sophora japonica has the word "ghost", so it is important that people only plant Sophora japonica in front of the door. As the saying goes, "plant Sophora japonica in front of the door to make money", and hospitals don't plant Sophora japonica either. But this is not absolute. As the saying goes, "There are ancient pagodas in the courtyard, which must be old houses." In the imperial garden of the Forbidden City, 18 locust trees before the Ming Dynasty were planted. There are many rules for planting trees in old Beijing. There is also a saying that "mulberry trees are not planted before, willow trees are not planted after, and ghosts are not planted in the middle to clap their hands (poplars)", but this means that these five kinds of trees are hard miscellaneous trees, which are not long-lasting, easy to deform and cannot be used to build houses. There is a TV series that reflects the story of old Beijing, called "Sweet Sophora in May", which is actually inaccurate. Sophora japonica mostly blooms in July and August, while Robinia pseudoacacia mostly blooms in May, originating from America and transplanted to Beijing in Qing Dynasty. It has no insects, no thorns, bright flowers and is widely planted, but it is far-fetched to say that it is the business card of old Beijing. The materials in this paper are mainly quoted from Chronicle of Beijing and Landscaping.