Thanks, you guys! I was afraid to leave the window boxes outside here, in Zone 5. I've tried planting bulbs directly in my balcony window boxes, and they don't come up. Same with pansies I try to overwinter, they don't come back either. So it sounds like I should just keep them in the garage and not worry about them. Hopefully they won't get too big. I'm still thinking I should probably cut back the watering to once a month or so.

Patience ... Home Depot probably got them packaged in a dark bag or box with no soil and they likely went dormant if not planted for a time. You only just planted them and started watering them. Give them time to wake up from the 'trauma' of being up-rooted and stuffed in that bag or box. Regards your other questions ... depending upon where you plant them, shade or direct sun, canna will grow quicker or slower. Sunny is best and it is recommended that they be in full sun to flower. Canna will live in shade, but may grow more slowly and refuse to flower. At least give them a partial shade environment if you are worried about too much very hot direct sun. Make sure your soil is not depleted by adding mulch if necessary. Late June isn't the best time to buy rhizomes, but knowing how hardy Canna are, even so, they will likely still be viable. If they fail to start poking up shoots after about 5 or 6 weeks, take 'em back to Home Depot with your receipt and get a refund. Try again in early Spring.

Okay, so I guess I'm not patient. Had it on top of the water heater for warmth and checked it out this morning...and there is nothing there. It just looked like a cacoon that a butterfly had left. Oh well, I tried! I am curious, are these really rhizomes on Mandevilla or just fleshy, water-storing "bulbs"(for lack of better name)?. I see them on spider plant and asparagus fern also but have never seen new plants emerge from them either. I have brought my mandevilla up from the basement and put it in the south sunny window and watered it yesterday. It has small new green growth buds so wanted to get it going so by time it is ready to go out, it will have some healthy growth.

Thanks for the great information. In addition, if you are storing canna rhizomes, they tend to store better on the warmer side at about 55 F. I store hundreds of cannas and elephant ears each year in the basement. Once I stored some cannas just above freezing and most of them rotted. As xerophyte mentioned, cannas should not dry out, unlike bulbs, since they are a tropical plant that does not go through a dormant cycle unless forced to because of freezing temperatures, and so their rhizomes depend on some moisture to stay alive and healthy.