Kairakuen is ranked alongside Kenrokuen in Kanazawa and Korakuen in Okayama as one of Japan's three great gardens (nihon sankoen). It sits on a plateau above Lake Senba and spreads over 13 hectares of plum trees, bamboo groves, cedars, and manicured lawns, with views over the lake from the garden's edge.
The garden is magnificent during the Mito Plum Festival, held over about a month from mid-February through late March, when over 3,000 plum trees of 100 varieties bloom in waves of white, pink, and deep red. The crowds on fine February weekends are substantial, but even then the garden is large enough to absorb them. Outside of plum season, the garden is pleasant but loses much of its reason for being — cherry blossoms in early April offer a secondary peak, and the autumn foliage is respectable, but the plum blossom period is what you should aim for.
Admission is free except during the Plum Festival (when a modest fee applies). The garden is a 15-minute walk from Kairakuen Station, a temporary stop on the Joban Line that only operates during the festival period.