Keisei Rose Garden is one of the largest rose gardens in the greater Tokyo area. Located in Yachiyo in Chiba Prefecture, it takes about an hour to get to from Tokyo. The 2021 Spring Festival, a flower festival, is on from April 23rd to June 13th. The best viewing period for the roses is from mid May to early June.
Keisei Rose Garden has approximately 10,000 roses of 1600 varieties. The roses are spread over seven mini gardens. During the period of the festival there is also some art work on display, including a large egg shaped installation. They also have some workshops scheduled for during the festival.
Admission is normally ￥500, but during the rose period they charge ￥1500 per adult. The festival draws thousands of visitors. They have a crowd checker on their website, that allows you check how busy it is on a given day.