Answer: Cannas need a very rich soil and plenty of water, meaning a deep soaking about twice a week rather than a daily light sprinkling. Larger rhizomes will produce larger plants. Good sunny weather combined with good care should yield an abundance of flowers from mid summer until frost. Nonetheless, I am surprised by the size of your cannas and I suspect they may have been mislabled. There are some dwarf types available so that is not an impossibility.
Cannas do not tolerate cold weather, but if they were in a sheltered spot and well mulched, they might have survived as they occasionally do in zone 7. You could dig carefully and see if they are still firm or if they are mushy. If they are mushy, throw them away. If they are firm, wait patiently for them to sprout when the soil warms up.
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