Brugmansia can have a very hard wood trunk. Gordon waits until the first light frost, then cuts off the green growth right down to the hard wood often going right into the trunk. He keeps about 24” of trunk on each plant, removes them from their large heavy clay pots, and places them in lighter plastic nursery pots for winter storage in a totally dark, cool spot—along with the cannas. This year, he didn’t pull them out of storage until late April, and, though they appeared quite dry and dead, they soon sprouted and reached record size with hundreds of blooms—they’re blooming now, as you see, above.
I must say these are my personal nightmare—I’ve never successfully saved the tubers. But here goes. Cut them down , remove dirt, rinse them, dry them, all very gently. Make sure the tubers you are saving have “eyes,” which show the beginning of a sprout. Separate the tubers from the stem and trim off excess material, including the roots. Bag your tubers in vermiculite, peat moss or wood shavings, completely covering them. Create small holes in the top of the bag for air circulation, and write the name of the variety of dahlia on the bag for identification purposes. Store your tubers in a covered box or plastic storage container at 45-50F (basements typically work), and check them twice during the storage period for rot and dryness. Remove the rotted tubers, but shriveling tubers may be given a few squirts of water from a spray bottle to keep them from completely drying out.
There you have it. I don’t know about the dahlias, but this year I’m going in big for overwintering. Thanks to Gordon Ballard and Brian Olinski for sharing their knowledge.