Posted: 11/08/2013 at 13:58
Its best to take cuttings in spring. Once they get hollow the stems won't root.
If you dig up your dahlia after the frost has blackened all the leaves, lay it on its side to dry a bit, and then store the tubers in a frost free place. This could be a shed or cellar. They don't need light until spring. If you have any cut surfaces dust with flowers of sulphur(also known as precipitated sulphur) to keep out fungal rot. I pack them in dry old compost, but you could use damp peat,or even just wrap in newspaper. If they freeze they will die.
In spring, bring into light and warm , pot into new compost, take basal cuttings from the new growth.