In many countries this starts in spring; even the desert gets transformed into a sea of flowers. The flower season can also depend on the geographic location.
The castle is one of the top 100 spots in Japan for viewing cherry blossoms. Blooming time is in spring: From end of March until early April. There is also a castle festival held annually during the blooming period, the Oshiro Matsuri festival with illuminated cherry blossoms at night from 6-9 p.m..
Special time of day tip: Every night 600 lanterns are illuminate the castle and its surroundings. It's a magnificent view.
Every year from April 1 until April 30 depending on the weather. General peak is end of the 1st week of April to the 2nd week of April. Some areas usually peak slightly ahead of others.
Best months are from April to August with a huge variety of amazing blooming flowers. However, worth a visit any season. Can be crowded on weekends during the summer. If you visit in summer, you definitely shouldn't miss the Rose and Light Festival (Rosen und Lichterfest): For one weekend in June thousands of lights illuminate the garden!