Dahlia tubers and canna rhizomes will likely rot in the ground over the winter, so once the foliage has blackened at the first frost, cut it off leaving an eight- to 10-centimetre stem stub (good for attaching labels). Then proceed as follows:
Dahlias: Leave them be for a week or so to allow the new eyes (growth points for next year’s stems) to develop. Carefully prise up the tubers (which are enlarged roots) with a shovel or garden fork, wash off the soil and set the clumps upside down in a cool place to dry. You want them to dry, not shrivel. It could take a couple of hours or a couple of weeks depending on conditions.
Discard tubers with no eyes, and trim off any long “tails.” Once they’re dry, write the name on the tubers with indelible pen (tags do go astray). Store them in the dark at a temperature between 4° and 8°C. Commonly, four or five tubers are placed in a plastic bag (pierced with small holes) with peat, vermiculite or sawdust, and the bags stored in cardboard boxes. However, one expert I know buries the tubers in vermiculite in Styrofoam boxes, and many growers wrap each tuber in plastic wrap and pile them in boxes. As long as the temperature is constant, condensation doesn’t seem to be a problem.
Cannas: Gently dig up each clump of rhizomes (which are fleshy underground stems) and let them dry for a few hours. You can leave the clumps with some soil on and wait till spring to clean and trim them, or you can hose them down and trim them before storing them. To trim, snip off the roots and any blackened or damaged bits. Particularly large clumps can be gently twisted or cut apart, but the bigger the clump the better the display next year. Store the rhizomes in barely moist sand, peat moss or vermiculite in the same conditions as dahlias.
Note: Check your stored cannas and dahlias monthly; toss out any showing signs of rot and spritz some water on any that look too dry.
Main image: istockphoto/OGphoto