Shuoshi was born in 1892, a number of years after Japan switched to the western calendar, but he seems to be referring to the traditional calendar in this haiku. Japanese roses bloom in spring and in the old Japanese calendar New Years would have fallen at the beginning of spring, so the idea of seeing roses blooming with the New Year was not a strange one.
Great Japanese Haiku my friend, I always learn something new from that wonderful country thanks to you, greetings.