Soon Time to Bring Tender Bulbs Indoors
Most summer-flowering bulbs other than lilies, and that includes dahlias, gladiolus, cannas, callas, acidantheras and tuberous begonias, are considered “tender bulbs”, that is, they are not hardy enough to survive the winter in cold climates. Some of these bulbs may well be able to overwinter outdoors in USDA zones 7-10 (indeed, some gladiolus thrive in zone 6!), but most of those for those living in colder zones, the only safe place to store them for the winter is indoors.
Usually the signal to bring them indoors is when the first frost damages their foliage. If there is no frost before mid-November, though, bring them in anyway: you don’t want them to be still in the ground when it freezes solid! To do this, dig up the root ball and shake it to knock off excess soil, then let the bulbs dry on newspaper for 10 days or so in a frost-free spot (a garage or shed, for example). Now clean them roughly with a brush to remove most of the dirt. Don’t rinse them, though: they must stay dry. On some bulbs, stems and foliage will fall off all on their own at this stage. If not, cut them off about 2 inches (5 cm) from the bulb. You can also sprinkle garden sulfur on the bulbs: this will help prevent rot over the winter.
If possible, store the bulbs in a perforated box so there’ll be a bit of air circulation, covering them with vermiculite, peat moss, wood shavings, or shredded paper. The ideal location for winter storage is a cool but not cold spot that remains between 45-55˚F (8-12° C) for much of the winter. That means that a fridge or a cold room is often too chilly for these bulbs, but a basement or lightly heated garage may work well.
You have nowhere cool to store them? Don’t panic: they can be kept at room temperature if necessary, but if so the bulbs will likely tend to dry out over the winter, so check them every month, giving them a spritz of water if they start to shrivel.