Winters in New Hampshire get far too cold for plants like cannas, dahlias and other tender annuals to survive. But you can save them from one year to the next by digging up their tubers or bulbs and storing them in a cool place for the winter.
Emma Erler, lead horticulturist with Kirkwood Gardens at Squam Lakes Natural Science Center and host of Homegrown NH, estimates that she digs up several dozen tender bulbs every fall.
“Once we have a killing frost and those plants more or less melt to the ground, then I get my shovel or my pitchfork out, and dig up those tubers or bulbs,” Erler said.
Gardeners who grow potatoes or onions will be familiar with how to proceed. After digging up the bulbs, brush away the dirt and let them harden off, or cure, in a place where it's warm and dry, but out of direct light for a few days.
“That allows the outer skin to get a bit tougher, and they’ll be set up to survive the winter,” Erler says.
An important step is to cut off any parts that are rotten, because that might end up destroying the bulb over the winter.
This is a good time to see if any of the bulbs or rhizomes have propagated, giving you the chance to divide them. This means more plants next year, and the opportunity to share with friends and fellow gardeners.
Finally, pack them in a container like a box or garden tote with either moistened wood shavings or shredded newspaper and put them in a cool, dry spot for the winter.
That might be an unheated basement or garage that stays at about 50 degrees. You don’t want to let the bulbs get below freezing.
“Occasionally over the winter I'll check to see if there are any rotten pieces, because just like one bad apple can spoil the bunch, so can one bad dahlia,” says Erler.
The dahlias and canna lilies at Kirkwood Gardens have been shared among the loyal garden volunteers for decades, a legacy that would surely please Grace “Sunny” Kirkwood, who began designing the gardens in 1995.
Homegrown NH is a collaboration between Squam Lakes Natural Science Center and NHPR.
