The ancients believed that climbing a mountain and inserting Evodia rutaecarpa on the Double Ninth Festival could repel insects, remove dampness and drive common cold away. So people wear cornus on their arms, or grind it and put it in sachets, and put it in their heads. Most of them are worn by women and children, and men in some places also wear them.

The relationship between the Double Ninth Festival and cornus was first seen in a story in the mythical novel "The Harmony of the Continuation of Qi": Runan people visited the scenery and learned Taoism with Fei Changfang. One day, Fei Changfang said to Huan Jing that there will be a great disaster in your home on September 9, and the solution is to ask your family to make a colorful bag, put cornus in it, wrap it around your arm, climb the mountain and drink chrysanthemum wine.

On the ninth day of September, Huan Jing's family followed suit. When they came home in the evening, they found that all their chickens, dogs, cattle and sheep had died, and the whole family was safe and sound because of going out. So cornus's "exorcism" was handed down.

Extended data:

The custom that cornus was nicknamed "to ward off evil spirits" and that cornus was admired by Chongyang was very popular in the Tang Dynasty. Besides wearing cornus, people also wear chrysanthemums. This has been the case in the Tang Dynasty, and it has been popular throughout the ages. In the Qing Dynasty, the custom of the Double Ninth Festival in Beijing was to stick chrysanthemum branches and leaves on doors and windows, "to remove evil and filth, so as to attract good luck". This is the vulgarization of the chrysanthemum on the head. In the Song Dynasty, there were also people who cut colored ribbons into cornus and chrysanthemums to give to each other.

However, after the Song and Yuan Dynasties, the custom of Pei cornus gradually became rare. The reason for its change is probably understood from the shift of the center of gravity of the Double Ninth Festival.

In the early people's time life, Chongyang emphasized avoiding evil spirits and eliminating disasters. With the improvement of people's living conditions, people not only paid attention to the real life, but also gave more expectations to the future life, praying for longevity and prolonging life. Therefore, the status of "longevity-prolonging guest" (Chrysanthemum) finally overtook that of "evil-avoiding Weng" (cornus).

References:

Baidu Encyclopedia-Double Ninth Festival