A 'hanamidou' is a hall set up in front of every Buddhist temple and decorated with many beautiful flowers. This tradition commemorates the Buddha's birthday on April 8.
 Kuraki uses some obscure 'kigo' (seasonal phrases) in this song. 'Saeka(h)eru' refers to the weather getting chilly again in early spring after a period of warming, so in this line, I translated it as the thin ice (ie, over a pond/river) freezing back over. Kuraki said in an interview that she wanted to evoke an idea of early spring with these words.
 'Chirazaru' means 'not scattered/dissipated'. I assume it primarily refers to the relationship between the romantic couple in this song, but it also hints at the scattered petals (ie, in 'the city of whirling blossoms').