Considered one of the three most important festivals in Kyoto, the Aoi Matsuri takes place on the 15th of May each year. Held by the important Kamo shrines, Kamigamo Shrine and Shimogamo Shrine, the origins of the festival can be traced all the way back rites performed to appease the gods and pray for bountiful harvests in the 6th century. It was established as a more formal annual event in the 9th century Heian Period when Kyoto became the capital and the Emperor recognized the importance of the Kamo shrines to the capitol’s prosperity. Because of the aoi, (hollyhock) leaves pinned to the participants’ hats, clothing, and carts, it earned the colloqial name of Hollyhock Festival over its original Kamo Festival title.
Source: Discover Kyoto