Cannas grow so fast when the time is right, I don't think I would make any effort to plant them before it's pretty warm out. They won't do much before then but take up a lot of space and time. I definitely have frugal tendencies so if they offer both tubers and growing plants, I'd get the tubers (assuming that's a significant savings) because I would be sure I'd have blooming plants within a couple months, maybe 2 weeks behind the already growing ones. The last time I excavated some to move elsewhere, it was about 3 weeks before I got around to putting them in their new home. Within 6 weeks, they were grown enough to make flowers, though definitely shorter plants than those left undisturbed.
I don't miss having to dig them up & store them in the basement like I did in OH. Brought them to AL and one of these days, I'll quit moving them almost every summer. It's not as easy to place them when they stay alive and are able to creep at will. They need a 'hard border' from which they can't escape, like concrete, or mowing. They're almost always seen around here in lone 'stands' right in the middle of a lawn. They really can't be a companion with anything else that I know. This summer I ran out of places to put them, so I sent boxes of them to several people, they multiply FAST (as long as they have the lateral space to do so.) It all started with a couple tubers a friend gave me in OH, now they're all over my yard down here, my Mom's yard & been mailed back to OH among other places. So the moral of all of that story is that you don't need much of a type unless you're impatient to have a ton of them NOW. In time, you'll have a ton of any kind.
One advantage of growing them out of range of hardiness is lack of canna leaf roller caterpillars. I don't do garden chemicals so daily patrols for these things are necessary if I'm going to see any flowers. It doesn't look like the problem will ever dissipate as the adults can fly. For that reason, I tell people about that if they think they're interested and live where they are hardy. A lot of them decide Cannas aren't for them if they don't micro-manage like that, and agree putting chems on these plants which could potentially poison hummingbirds (which are attracted to the nectar/blooms) is a cruel idea. Probably unlikely but already-growing plants could have these caterpillars or unhatched eggs. That would only be a problem the first year, AFAIK, and then only until they are eradicated by the gardener, but something to look for if one is getting plants vs. dormant tubers. It's not a reason to not buy them, especially if you know the climate can't support them in subsequent years, just something to know so they could be removed from the plant if found.
For comparisons' sake, if the diff kinds grow at diff rates, the kind I have are plain species C. indica, large plain green leaves, smallish fire-engine red flowers, get to about 7 feet tall here though if I ever left them alone for a few years, they might be a bit taller, but I haven't seen a really tall patch of this kind. Sounds like the same kind Ken has. I drive by patches with other flower colors that do get a lot taller. How tall do yours get, Ken?
This patch has been in place since late summer '12. This pic is from 9/3/13. At the far end you can see some 'Cleopatra' I got from a friend just over a year ago. Haven't had those long enough to say much about them except that the flowers are incredible, about 3x the size of the red ones, and look hand-painted in yellow/orange stripes and spots. The leaves are known for the random red spots/stripes. A pretty one!
