I went to Takinoue and Kamiyuubetsu on May 23rd July.
Takinoue (滝之上) and Kamiyubetsu (上湧別) are very small towns which are located near to Monbetsu (紋別), the nothern part of Hokkaido.
Takinoue is popular with its pink moss, beside than Oozora near to Abishiri (大空, 網走) while Kamiyuubetsu is popular for its large scale of tulip farm. Both of the flowers are blooming in about the same time, end of May. I was lucky because at the day I went there, the weather was really nice with clear sky. However, when I reached Kamiyuubetsu, the weather started to change with cloudy and strong wind.
Here for more info --> takinoue and kamiyuubetsu