From animelyrics:

[1] 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.
[2] 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.
[3] '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').