Unlike most other garden flowers, the shorter days of autumn spur dahlias into glorious bloom. Cut bouquets or a single blossom to enjoy indoors, share them to brighten someone’s day, and visit them often to admire their fascinating diversity of form and colors…and all from such a humble beginning last spring! In warm areas dahlias can be left in the ground through winter, but they are not hardy in zones 7 and cooler. It’s fine to treat them as an annual, replacing them in the spring as you would a geranium or fuchsia, but if you’d like to try storing your tubers over the winter, here are our tips.
It’s best to wait until a week after frost first blackens their foliage before digging your tubers as this will give them time to harden off in the ground. Cut the stalks off to a few inches above ground level. The tubers are likely to have grown into larger clumps over the summer, so start digging at least a foot away from the stalks and work carefully. Tag each clump with the variety name, wash off the soil, and allow it to dry in a cool place for roughly a day.
If you like, you can divide the clumps with a sturdy knife at this point, making sure that a piece of the crown (the thickened area where the stem meets the tuber) remained attached to every division since that’s where the eyes for next spring’s growth are located. You may want to dust cut sides with a fungicide like garden sulfur; at a minimum, allow cuts to air-dry for a day before storage.
You can store in plastic grocery bags, in boxes lined with a plastic garbage bag, or in covered plastic storage containers – something that will protect them from dehydrating. Pack in peat moss, coir, wood shavings, coarse vermiculite, or a blend as we do. Store in a cool, dry, dark place, ideally at 40-45F. Check them every now and then to allow moisture to escape if you see condensation or to sprinkle some water on the tubers if they seem to be shriveling.