Looks to me like it is a relative of the regular Dahlias we plant for summer. From the sounds of it they recommend leaving them in the ground so that they have ample time to bloom. That is out for us, the coldest zone you might get away with that is zone 8 and mulch. You could probably grow them here with your regular Dahlias (if you can find them), but you probably wouldn't get any blooms. Most of us get frost in September and by the sounds of it even in warm countries they don't bloom until the end of September or October.

When I googled tree dahlia I found lots of information.

Syreeta