FROST may well spell the end to the fantastic displays of Dahlia flowers we have been enjoying in our gardens this summer, but on the upside our Dahlias need to have a clear signal that it is now time to stop and have a rest over the winter. You need to allow your Dahlias to be blackened by the frost before you cut them down (leave about 5 - 6 inches of top growth).
Many people now suffer the dilemma of whether to leave them in the ground or dig them up - if you are blessed with a sheltered garden where the soil doesn't freeze solid in winter and is free-draining then all you need to do is apply a thick mulch - a mulch of 5cm /2 inches of garden compost, leaf mould, straw. Now, if you have a heavy clay soil or you live in a frost pocket then dig them up after they have been frosted, cut them back, clean off the excess soil and then place them, upside down to allow them to drain, in a cool, frost free, dark shed. After a few days you can place them in a tray or pots and cover them with some compost or something similar to stop the tubers from drying out completely.