Mt. Ryokami is a mountain in the Chichibu District of Saitama, and Mt. Ryokami Fumoto Hana no Sato is a flower garden sitting on the mountainside in the town of Ogano. They grow numerous varieties of dahlia here, including ones not easily seen elsewhere in Japan. There are 5000 dahlias in the 10,000 meter squared dahlia garden with 350 species of the flower on display.
The garden is open annually from September 1st to November 3rd. Please note that on days of heavy rain, the garden often closes. You can check for the most up-to-date information on the official site here. It is 400 yen for admission to the garden for anyone older than 15 years old.