It depends on how cold a winter you get and how well drained is your soil. What they really hate is a cold wet clay soil. We used to dig ours up when we grew them on a solid boulder clay, but they survived when we moved to a pure sand soil. Take your choice.

Theoretically, yes you're suppose dig them up when it gets too cold, less than 50°F, and somehow store them overwinter to replant in the Spring. That never works for me; too dry, they turn to saw dust, too moist, they rot out. I haven't figured out the right technique so I just leave them and buy new ones next spring. That's the easiest way for me. Sorry, not too helpful, but I'm honest.

Well I think I’ll take a chance and leave them,though I do remember my Mum digging hers up and storing in garage.That memory just came to me as I was reading your reply.
In reply to Owdboggy,we have Sandy soil so here’s hoping.

I have a a reasonably draining soil and I have left some in the ground but I buried the tuber twice the depth recommended and they have survived. The others are taken into the greenhouse and left upside down to drain and dry out. after a month I knock them out of the pot and clean them checking for slugs etc. They then get put back into their pots packed with sawdust. they stay under the staging until March when they get potted up in fresh compost.

I have several old varieties that I'd hate to lose so it is worth the 20 mins each plant takes.

Do you mist them? I tried storing mine in the basement under the stairs, wrapped in newspaper and in a cardboard box. When I went to check them (mist them) in December, they shrunk to a dustball. Another time I would mist them weekly and they rotted out.

No I just left them in the unheated greenhouse that rarely gets warm in the winter. The sawdust does absorb a bit of moisture but not enough to cause the tubers to rot.

I've left mine in their pots to dry out in a shed. Worked every time - except when the roof leaked on to one . Of course that one rotted.

I live in Scotland so I lift mine.

I leave mine in the pots in my greenhouse. In March I lift them, wash them and put them in new soil.
I have had the same plants for years.

I always used to dig up the tubers and store them in the shed, with varying degrees of success. As our winters are getting milder here in London I've been leaving them in the ground for the last couple of years and earthing them up with bark chips and they have survived. However, in time, they'll get larger so they get dug up in early spring and get divided (butchered) up to start off in pots. Often there's so many emerging shoots that it's trial and error, and tubers get sliced in half to accommodate them in the pots. I dust the cut surfaces in yellow sulphur and leave them for 24 hours before planting up.