I'm not sure if you've understood the notion of transience and ephemerality which cherry blossoms evoke in the national psyche. They are celebrated precisely because they don't last long.

Please refer to the map here and consider getting a JR pass to travel up to Aomori if you're serious about seeing Sakura.

Yokoso flyertalk gift!

You might get to see the wisteria, and Tokyo will be alive with azalias.