Dahlias are right at home in sunny flowerbeds with their long stems and large, colorful blooms that last throughout most of the second half of the growing season. Whether a gardener grows dahlias as a border display or a backdrop for other shorter flowers in a landscape arrangement, dahlias will reward modest work with a big show. When summer gives way to autumn, it is time to begin the work of assessing your dahlias and saving the dahlia tubers indoors over the winter.
Assess the growing dahlias at the end of the growing season. If there were plants that did not grow well, remove them from the ground and discard them (rather than save these tubers). Do not compost plants that may have viruses.
Cut the stalks down early in the day so that only approximately 2 inches remain above the crown. As you work, make sure you label the dahlias if you grow different dahlia varieties because they will become impossible to differentiate without the stalks.
Dig up the dahlia tubers carefully after allowing the cut stalks to sit for several hours. This will enable you to handle the tubers more easily because they will not be as fragile. Loosen the soil around all of the sides of the tuber (approximately 12 inches away from the center of the plant). Work the spade under the tuber and carefully pry the tuber from the soil. Shake the tuber to remove excess soil and turn it upside down to allow any moisture to drip out of the cut stalks.
Spray the tubers with a hose to remove excess soil. Leaving soil on the tubers might contribute to viruses infecting the tubers over the winter.
Divide the tubers before storing them for the winter. Work on one tuber at a time with the knife to prevent spreading viruses between tubers. Cut off the entire stem and then examine the mother root. Each portion of tuber you cut from the mother root must have a part of the crown and at least one eye. Cut off pieces that are large or small (if they are small they must just be large enough that they will not shrivel while in storage). Cut off all small feeder roots from the tubers (these contribute to decay). Look at the crown area to find discolored areas. If you see this discoloration, discard this tuber because it is not viable. Work to divide all of the tubers, sterilizing your knife between tubers. Sterilize the knife by holding it over a flame and then allowing it to cool.
Wash the newly divided tubers again. Cut the ends of the tubers and look again for discoloration. If you find this, cut up toward the crown. If the discoloration stops around the crown, the tuber should be viable. If the discoloration continues around the crown, discard the tuber.
Treat the cut tuber ends with a fungicide before storing. Follow package instructions for mixture amounts and the recommended length of time to dip the tubers to protect them during storage. Label the tubers and allow them to dry for at least 24 hours in a location where they will have ventilation surrounding them on all sides (a rack).
Store the dried tubers in plastic bags filled with coarse vermiculite. Fill the bags with some vermiculite, add several tubers and place more vermiculite in the bags. Make sure every bag has equal amounts of vermiculite and tubers.
Place the sealed bags in brown grocery bags and store in a location with constant temperatures between 40 and 45 degrees Fahrenheit. Inspect the tubers once a month and discard any tubers that are decaying.