two choices---dig up the 5 that show no signs of growth to see if they've rotted, etc.... or just give them more time, canna's don't always take off the fastest. I potted up 11 of them three weeks ago and only have 5 up so far.

How can I tell if thay have rotted? Can I put it back if it is not rotted?

Just dig into the pot till you see the top of the rhyzome. If it's bad, it will either be dark and sort of dried out, or conversly, it may be mushy and rotted.

If you planted healthy rhyzomes, they will almost always come up.

Which begs the question, what condition where the rhyzomes when you planted them? Were they firm and robust looking, or were they dark and mushy?

I looked at some of the rhzyomes by taking a little soil off at a time. Three of the five had a small green shoot starting to come out, which was nice to see. No growth from other two which are Durbans or tropicanas.

I covered the first three back up with a small layer of soil, will they continue to grow?

The tropicana had roots and they were firm not mushy, will they catch up?

Well all that sounds good. Fact is, some rhyzomes jump up and some are real slow-pokes. So I'd leave them be, keep them in a fairly warm spot and do not over-water them.

All the water that the plant needs to start is in the rhyzome. So let the soil dry out before you re-water. I think at this stage the only thing that is going to hurt the plants is too much water.

Good luck!