Overwintering runner beans

[ameno]

When should one expect overwintered runner beans to start sprouting?
I have 18 in the ground which I have overwintered, and they seem like they are probably still alive. I dug down carefully to take a look at two of them today, and the tubers are still firm, whole and pale in colour, as they should be, but there is as yet no signs of shooting.
So when is normal for them to start growing again? I want to know how many are definitely still alive so I know how many new plants I need to sow.

[Bren In Pots]

Ameno I've often found some that have stayed in the ground and sprouted what I usually do is to dig a few plants potting them up and leaving them in a unheated GH until the frosts have passed.

This photo was taken May 14th the other year.

[ameno]

When do you dig yours up? Do you think it might be worth my while digging them up now, potting them up, and putting them in my conservatory?

[Bren In Pots]

I dig them up after the beans are all harvested that includes those I'm saving for seed so its late-ish in the season. You could dig yours up or maybe cover them with fleece if you don't want to damage the roots.

[ameno]

Dug out my been roots today, to take home and pot up.
All looked still to be alive, but I discarded two of them (one because it was tiny, and one because I accidentally cut it in half with the spade). A few of them are already just starting to sprout.

[Bren In Pots]

Thats good news, it sounds like they'll survive. and produce bushier plants than this years seeds mine seem to throw out around 4 or 5 stems each plant.

[ameno]

An update:
14 of my 18 potted up runner bean tubers are sprouting, and three more have rooted but are not sprouting just yet. One was showing no signs of growth when I turned it from its pot, so I ditched it.
One of them, the biggest, is already almost 2 feet tall...