Dahlias provide late-summer color, but their fleshy tubers are sensitive to frost and winter wet. In dry, sandy soils, you can leave them in the ground, but in heavy, wet Leitrim clay, leaving them outdoors often leads to rot.
To overwinter them safely, lift the tubers in autumn after the first frost has blackened the foliage. Cut the stems back to 4 inches, dig up the tubers gently, and brush off the soil. Turn them upside down for a few days to drain water from the hollow stems. Store the dry tubers in boxes filled with dry compost, sand, or sawdust, and keep them in a frost-free shed or garage. Replant in pots in spring to get an early start.