it maybe how you store them pete, i store mine every year in dry compost under the garage/shed bench in a bucket . they are covered by 3-4 inches of completely dry compost to keep the frost/cold off..

Could the warm dry place be TOO warm?

They need to be cured, but not dessicated. I wash them outside to get ride of most of the earth on them then hang them for 2 weeks or so in the garage (it is pretty humid in there).

I store them in sand but my mum used to store them in shredded paper in a box in the cellar -not heated. They need some humidity to keep them going as they are tubers and would get some moisture in their native earth. If your garage gets freezing, then store them in a shed - the height will take a few degrees off the temp and more than sufficient for tubers.

I meant store them on a shelf, not shed!

Useful info folks..thanks. I store/overwinter a lot of things in my cellar also. Dahlia tubers too now,once my pals have lifted theirs. Had no frost here in Shrops yet..but not getting complacent!

thanks everyone i covered them in shaveings last year but they all rotted ? before that under my bed in news paper i cant understand it ?