To prepare your dahlias for winter storage, cut the stems 6” inches or so above the ground after the first killing frost.
Allow tubers to remain in the ground for another week while the roots wilt slightly and the necks (the narrow, tapered end next to the stem) lose some of their brittleness.
To dig them up, force your fork into the ground on all four sides of the clump, gently lifting at each position.
Set the clumps in a dry location for a day or two. The soil will fall away, revealing the tubers clustered at the base of the stem.
To divide the clump, find the largest or most easily accessible tuber and cut it away, along with a bit of the stem.
In the same manner, cut off the other tubers, careful not to break the necks.
The tubers from each clump may be labeled, wrapped in newspaper, and placed in a bushel basket for storage.
An alternate method (the one which I prefer) is to label each tuber individually and place it in a box containing dry peat moss.
Each tuber must be completely surrounded by peat moss.
Place the baskets or boxes of tubers in a dry place where the temperature is a constant 40° to 50° degrees Fahrenheit.
Examine them frequently during the winter. If the tubers shrivel badly, sprinkle a little water on the peat moss, unwrap the tubers stored in a newspaper, spray a little water directly on them and rewrap.
But be careful. Too much moisture will cause decay or start the tubers into premature growth. The same is true of high temperatures.
44659 by H. B. Schell