Cherry Blossom season in Japan lasts from March through April, with the blossoms (sakura) usually in full bloom by April 1.
The best places for cherry blossoms in Japan are as follows:
Best Places for Cherry Blossoms in Tokyo
Best Places for Cherry Blossoms in Kyoto
Best Places for Cherry Blossoms in Osaka
Expo 70 Commemorative Park
Kema Sakuranomiya Park
Osaka Mint Bureau