Each year from the mid to late May timeframe, Uonuma's Negoya Flower, Greenery, and Snow Village (Hana to Midori to Yuki no Sato) hosts a festival dedicated to moss phlox, also known as shibazakura. Approximately 200,000 of the flowers blanket the grounds of the spacious park in shades of pink, white, and red, creating a colorful patchwork quilt appearance to the hillside.
There are several great vantage points across the park to appreciate the flowers in all their glory, including a dedicated observation deck where you can view them from above.
There is no specific admission fee to enjoy the event, but donations of ¥300 are suggested to help maintain the park grounds. Visitors who make a donation receive a commemorative postcard as a thank you.
I've said this before - the texture is amazing. If you get a chance, pet it gently. It's so velvety soft.