Hanami (花見) is the Japanese word for flower viewing. While the word may be used for the ancient practice of plum blossom viewing, it is generally used to refer to cherry blossom (桜, sakura) viewing.
The exact timing of cherry blossom blooms varies due to location and weather patterns. Each year private organizations will release forecasts for anticipated peak blooms. Even within Yamanashi, different areas tend to bloom at different times. For example, areas such as Kose Sports Park in the Kofu Basin will likely bloom (and end) sooner than cooler areas such as Hokuto. Generally, cherry trees in Yamanashi will blossom from late March to early April.
Yamanashi is famous for the Jindaizakura (神代桜), a 2000 year old cherry tree located at Jissō-ji Temple. It is located closest to Hinoharu Station which is about a 15 minute drive away.
Kose Sports Park is a centrally located public park with many cherry trees. The area can become crowded, especially on days when sports events take place. Kose Sports Park is one of the earlier places to bloom in Yamanashi. Kose Sports Park is popular with families due to its large grounds and playground area. It is a 30-40 minute walk from Kaisumiyoshi Station.
Ooboshi Park is in the town of Fujikawa in the northern part of Minamikoma. The approach to the park includes a winding drive or a long walk up the hillside. The area is known to be one of the Top 100 locations for hanami in Japan. Due to its elevation, this Ooboshi Park cherry trees may bloom later than areas lower in the basin.