Double Ninth Festival dated on the ninth day of the ninth month in Chinese calendar, is a Chinese holiday, mentioned in writing since before the East Han Period.

According to the I Ching, nine is a yang number, ninth day of the ninth lunar month or double nine, has too much yang and is thus a potentially dangerous date. Hence, the day is also called "Double Yang Festival". To protect against the danger, it is customary to climb a high mountain, drink chrysanthemum wine, and wear a plant named zhuyi. Both chrysanthemum and zhuyi are considered to have cleansing qualities and are used to air out houses and cure illnesses.
Double Ninth may have started out as a day to drive away danger, but, like the Chinese New Year, ver time it became a day of celebration. Today it is an occasion for hiking and chrysanthemum appreciation. Stores sell rice cakes (a homonym for height ) inserted with mini colorful flags to represent zhuyi. Most people drink chrysanthumum tea, a few old schools drink homemade chrysanthemum wine. School children learn poems about chrysanthemum, and many cities will host a chrysanthmum exhibit. Mountain climbing races are also popular, winners get to wear a wreath made of zhuyi.

This is an often quoted poem about this holiday: Double Ninth, Missing My Shantong Brothers - Wang Wei (Tang Dynasty)

Alone, a stranger in a strange land, Every holiday the homesickness doubles. Far away my brothers have sent word: They have gathered on mountain tops, They are going around inserting zhuyi branches, They are missing one person.