Kairakuen Garden, located in Ibaraki-ken, is one of the best places to see Plum Blossom during the begin of Spring. Besides plum blossom you can also visit a beautiful, traditional house which gives you a nice view of the surrounded nature. One side of the garden is filled with bamboo and there are food stalls selling all kind of sweets and snacks.
Kairakuen garden is easy to reach from Mito Station (if you’re coming from Tokyo, take the Joban Line at Ueno Station). Once you’re at Mito, take the bus for 15 minutes or take a 30 minute walk toe the park. There is an information desk at Mito station, where you can get a map. Free entry.
For more information, check their official website: http://www.koen.pref.ibaraki.jp/park/kairakuen01.html