We all know the japanese cherry trees (sakura), but we sometimes tend to forget their importance in japanese culture!
These trees, which are blooming no longer than 3 weeks per year, are for the Japanese the sign that the spring is there. They are source of happiness and of many parties. An important tradition in Japan is to get together and watch the cherry blossoms, which is called hanami.
The blooming period of cherry trees is around end of March and beginning of April (it varies among regions), and it is the season I recommend to visit Japan.