In Japan, Buddha’s Birthday is celebrated on April 8, but is not a national holiday. On this day, all temples do celebratory events/festivals called 灌仏会 (Japanese: Kanbutsu-e), 降誕会 (Goutan-e), 仏生会 (Busshou-e), 浴仏会 (Yokubutsu-e), 龍華会 (Ryuge-e), 花会式 (Hana-eshiki) or 花祭(Hana-matsuri, meaning ‘Flower Festival’). The first event was held at Asuka-dera in 606. Japanese people pour ama-cha (a beverage prepared from a variety of hydrangea) on small Buddha statues decorated with flowers, as if they bathe a newborn baby.
– Wikipedia