In Japan, April is the beginning of the school year as well as the business financial year. Since the Heian Period (794-1185) flower-viewing parties were popular among the aristocracy. In the Azuchi Momoyama Period (1568-1600) the cherry blossom viewing spread out to the rest of the population.
Cherry-blossom viewing began in ancient times when aristocrats wrote poetry and sang songs under the flowering trees. It has been the theme of numerous literary works, dances, and paintings. Even though modern parties aren't so refined as those of the past, people still find the blanket of light-pink petals deeply moving.

The Japanese like cherry blossoms because the shape and color of the petals reflect people's ideal notions of purity and simplicity. They are also touched by the blossoms that are so fragile and short-lived, scattering just a few days after they flower. Every time there is the slightest breeze, a shower of cherry-blossom petals is produced.
Hope this is enough data about how hanami was born



sources : http://www.asij.ac.jp/elementary/jap...ami/hanami.htm and http://web-jpn.org/kidsweb/calendar/april/hanami.html