There was a hard frost last night that killed the dahlia tops. I’m going out of town and won’t have a chance to dig up the roots for at least a week. Is that too late to save them?
For the tuberous roots of dahlias to be damaged, the soil would have to freeze several inches deep — something that usually doesn’t happen until a month or two after the first frost. (In USDA Plant Hardiness Zones 8 and warmer, it may not happen at all.) So you can delay this task a few weeks without worry.
Here’s my technique for storing tender bulbs, including dahlias and cannas, through the winter. Caladiums, tuberous begonias, elephant ears, and gladiolus prefer a slightly warmer storage temperature of around 50°F. —Doug Hall
How can I keep my dahlia roots for next year? Frost killed the tops last week. I spent good money on the roots and I’m not willing to let them become expensive compost.
I’m with you. It takes just a few minutes to dig and store dahlia tubers, so why not keep them for a repeat performance next summer? Dahlias survive the winter outdoors in Zone 9 and warmer; everywhere else, you can dig up the tuberous roots and overwinter them indoors. The same technique works for cannas and other tender summer bulbs.
After frost, cut the stems to stubs. The sweet-potato-like dahlia tubers extend outward from the stem about 6 inches, so be careful not to slice into them while digging. Shake the soil off the roots and let them dry in the garage for a few days. If you have more than one variety, write their names on the tubers with a felt-tip marker.
Some gardeners divide their dahlias at this point, leaving one growth bud or “eye” per division and dusting the cut surfaces with garden sulfur as a fungicide. I prefer to store dahlia and canna clumps intact, waiting until spring to divide them, because I’ve had better success that way.
Pack the roots in paper bags or cardboard boxes with dry sphagnum peat moss, sawdust, or vermiculite surrounding them. Store them at a steady temperature between 35°F and 45°F. Back in the days of unheated, damp basements and root cellars, it was easier to store tender roots without their shriveling. Nowadays drier basements prevail, and it’s wise to check on the stored roots monthly. If they start to shrivel, lightly moisten the sawdust or peat. —Doug Hall