Ask-a-Dave's-Gardener: Cassia Alata aka CandleBush and overwintering, 1 by tdot

tdot wrote:
I have a number of these beautiful plants that I germinated this past spring. The seeds are straight from Kakum National Park in Ghana, West Africa. My babies seems to love the summer here in Toronto, and have grown quite quickly.
I actually have two questions:
First, one is not opening his leaves. He's still got new stems growing daily but his leaves won't open, even in direct sun. My guess is I need to transplant him into a larger pot? It is quite a small container.
Second, what do I do when it gets downright cold here?! I want to move my babies inside; they bring me so much joy, I'm not ok to losing them to winter. Has anyone successfully overwinter these plants (in Ghana they are called Simpis)?
Thanks for any and all advice :)