They should be fine at those temps. I have had mine outside in cardboard boxes (without a greenhouse) for 1 1/2 weeks with temps similar to yours. If there is a frost warning, you can cover them up with a heavy blanket.

Ok, thanks! How exciting to finally get some out!

Where I live in zone 4, I usually plant my cannas outside from the last week in April through the end of May. Almost every year, we get a hard frost in May that knocks the cannas back that have not been covered. However, they recover very quickly and end up being just as far along as those that do not get covered.

cannas seem to be ok until about 20 F. I lost many last winter due to about 3 days below 25. This year I have new plants. I covered them with about 3+ inches of decorative bark. Hope they survive.