Ah, I grow a lot of tender perennials with large storage systems (corms, tubers, etc.) and to be perfectly honest, there is little you can do to a canna to diminish their essential vigour. Same with dahlias. Cannas have been expanding their rhizome all summer and will be twice the size they were at the start of the season. Dahlias especially - I can totally see why they were considered an edible food source.

We are having a glorious autumn and it pains me to have to dig up plants in full flower but needs must - I am out of time and space so up they come. I wouldn't fret, Doris - you can dig up the cannas in the garden with no real concern that you are damaging them for next season. I would probably drag the pots under cover and leave the cannas in their pot.

I should say, I don't grow cannas myself as it became really quite difficult to find a source which was not virused in the UK, so I haven't had any for 20 years or so - might be worth checking out whether the issues with virus have been addressed by suppliers.

With cannas, it's most desirable to wait until at least a couple of frosts have knocked back the foliage and the rhizomes have been encouraged to enter dormancy. Also, the longer the storage period, the more likely it is for problems to develop i.e. rot. That said, most times you can probably cheat a bit at the end of the season without difficulties arising.

More here:

https://rustyblackhaw.substack.com/p/the-relaxed-gardeners-guide-to-growing

Thank you Rusty for your valued information here and in your link. I will keep this in mind.