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The plum tree bent under the winter freeze, With showers, all at once opens its buds. The moon, through mists, projects its shadow In the dark, breezes carry its scent. A few days back, the trunk was buried in snow, Now, branches bear flowers anew. Through hardship and the bitter cold - This dignity, at the forefront of spring.
By Zen priest Hakuin (1685-1768) in his commentary on the Heart Sutra.
I guess the plum blossoms spring forth with the first spring rains.
Soshitsu XV contrasts the plum blossoms with the exuberance of the cherry blossoms, and finds the plum blossoms more refined, elegant, noble; the restraint of the scent and the blossoms thus give a sense of profoundness.
It is seen as a symbol of struggling and enduring through the winter (of our lives), and bring forth after this hardship something dignified.