According to Dahlia Barn, the most important things about dahlia tuber storage over the winter is that they do not freeze and that they are dry before being placed into storage. Pack the dahlia tubers into a box filled with peat moss or another dry storage packing material such as newspaper or paper or plastic bags. Keep the tubers in an area with medium-high humidity to prevent drying out.
Temperature for the storage of dahlias ranges between 40 and 50 degrees Fahrenheit, according to Dahlia Barn. Avoid the use of outdoor sheds or storage where the risk of freezing is present, and instead, choose a location in a basement or cellar that maintains a cool temperature. Check the tubers once a month throughout the winter to ensure that they are healthy. If the tubers show signs of shriveling, spray them with a mist of water from a squirt bottle.
Remove dahlias from the ground for storage only after the ground has frozen in the fall. Feeling the cold of the ground is integral for the lasting storage and health of the dahlia, and it is recommended to wait until the foliage has completely died back and turned black before removing the tubers. Once the ground is thawed in the spring and the chance of frost has passed, divide the tubers, allowing three to four days for the cuts to dry out. Plant the dahlia tubers when the time is correct for the growing season of the particular region.