I would base the tree's sudden springing into life on coincidential poignance (just like in the movies). Poignant since, as you already know, Rory cared for Cream in the three of the most happiest years of her life after she was released from jail. Yes,
Nocturnal was not kind to her.
The tree sprung forth through the magic of biology, HotD. Jesus, watch the
Discovery channel more, will you? Lavender, because it's a nice color.
Cream knew because Rory told her one day while traversing the outskirts of Way Town looking for food and shelter when he saw a similar lavender tree. He just pointed it out because he's kind like that. Yes, like Bomb. Kind like Bomb. Gentlemanly like Bomb.
...Eh. Too bad those other hobos beat his ass to death, huh? Shameful. Cream was crushed. She was stomped. She was whipped.
Yes. Whipped Cream. HARHARHAR
Well, if you have any more questions, I'll be more than happy to answer them, lest you stuff a marshmallow in me and I die yet
another horrible death...