Dallying with the dahlias. A memorable line from Somerset Maugham, I think. Travels with my Aunt, I believe. For some time out-of-favour with gardeners, dahlias are making a comeback.
The general advice is to lift plant tubers in autumn to store over winter. Plants can also be left in situ. Use straw for insulation, applying a thick layer of mulch to protect roots from frost.
We planted a couple of dahlia early summer 2018. One plant survived – in a sunny patch under the far cherry tree. It’s produced deep red flowers. Not huge dinner-plate dahlia sized, but lovely all the same and quite surprisingly visible from the flat through the window.