This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
In a treatise on this flower, recently published by Groom-beu>gk, the cutting down is recommended " not to be performed until the first frosts have completely checked vegetation. For choice, good varieties, it is an excellent plan," says the authority, "to place a small hillock of dry ashes round the stem of each plant This protects the embryo buds both from any sudden severe frosts, and also carries off to a distance the heavy autumnal rains. In wet grounds especially, this is a good and useful application, though in high dry land it may not be absolutely necessary. Choose some dry morning, when there is a probability of a dry following day, and cut down the plants within one foot of the ground. The day following take up all the roots so cut down, and turn them upward to allow the watery sap to drain from the stems. Bring them in under cover, and see that the numbers or names are all securely tied to the stems with copper wire. Mat or twine is not good for this purpose, because it will soon rot, and the name may easily be displaced or lost - a matter of consequence to such as wish to keep their plants true to name. The roots should all be taken up on the same or the following day, in order to become all dry together, so that they may be put away for the winter at once.
Let all the soil be carefully picked out from among the tubers without wounding them. As soon as they are quite dry, and before they begin to shrivel, fix upon a place to store them away. A dry cellar is best, because there is, in such a place, just sufficient moisture to keep the tubers fresh without shriveling, and the buds alive. Pack them with their stems downward, and cover them up with dry clean straw, several inches thick, a layer of roots and a layer of straw between and under each layer of roots. In these winter quarters they may remain till the season for starting them into growth returns. They should be looked over about once a month, and all decaying roots and rotting stems removed, and fresh dry straw laid upon them to absorb any moisture; this is the best method of keeping Dahlia ground-roots. Pot-roots should have their tops cut off, and the pots laid on their side in a place where the frost can not have access to them. If the amateur has a green-house, these pot-roots can be conveniently stored away under the stages, laid on one side: no water that may run through the stage from the plants will injure them. Pot-roots keep better than ground-roots, and therefore it is desirable to have a' few of each variety struck later for this purpose.
If the amateur has no cellar for his ground-roots, nor a green-house for his pot-roots, he may store the former away in boxes, in a dry chamber, or in any out-building, provided the frost can be kept from them by some kind of covering, such as old carpet? or garden mat?. In such places they will require more frequent looking over, to remove all decaying roots and stems. - London Gardeners' Chronicle.