The message
from (Nick Maclaren) contains these words:

I left some in the ground a year or two back. It was a mild winter,
but all died. I would expect the same for roots in a tub, as I
believe that the damage was consequent on freezing.

My guess is that you can do this only when you can ensure that the
roots will never freeze at all.

Runner beans are very tender and the lightest frost will kill them. The
year before last i was too late, and while the roots looked OK when I
put them in the sand, by the end of the winter they were all black,
mushy and smelly.

This last winter I cut and dug them before any frost hit them, and every
root has grown. I kept the tub in the kitchen over winter, and in the
shed from mid February. (Clay lump and pantile shed.)

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