One of the most spectacular of autumn flowers – dahlia – unfortunately is not hardy enough to overwinter outside. However, be in no rush to lift them – many late-season blooms will still be produced during warm autumn days; while minor frosts cause little damage to dahlias, if their tubers are mounded.
Start lifting dahlias, when autumn frosts become regular, or when a prolonged cold period is forecasted. Depending on the weather conditions, sometimes dahlias need to be dug up in mid-September, but last year and this year they will keep flowering until late October.
Using a garden fork, lift the dahlia clump from the ground and leave to dry in the sunshine, or bring them inside, into a dry and ventilated place, such as a greenhouse. Clean tubers carefully in 5-6 days, removing any damaged and diseased parts, and cut the stems down to 2-4 cm. Sprinkle cut surfaces with crushed wood coal, and keep the tubers warm (20-25C) for another week, to give the cuts some time to heal.
There are several ways to keep dahlia tubers through the winter. Line a square box (80x50x60cm) with paper, spread a 3cm layer of dry soil or peat and place a single layer of dry dahlia tubers. Tubers are best stored at temperatures of +1+7C and humidity of 80-100 %, covered by a layer of soil, sand, peat, perlite, vermiculite or sawdust.
Dahlia tubers can be stored in open boxes in a cellar (+3+6C, humidity of 70%). The cellar should be ventilated 3 times a week for 20-30 minutes, alternatively, an air fan should be installed. .
Gardeners know a lot of ways to store dahlia tubers throughout the winter, however, a number of plants still rot. The decay starts from the stalk stump, and later reaches the point where the tuber connects to the main stalk. The rotting tuber is not easy to detect, therefore the rot spreads rapidly until the whole plant is lost. The rot can be avoided – peal off the bark of the stump and carefully remove all of the soft tissues, then leave to dry for 2 or 3 hours.
Tubers rolled in clay paste usually survive winter well. After you dig the tubers, shake off the excess soil and dry them for several days, as described above. Clean them carefully and soak for 12 hours in a strong solution of permanganate of potash. Remove then, dry briefly and dip in slurry of clay and fungicide, made to a consistency of sour cream. Dry briefly until the coating sets. Store in a cool cellar. In spring knock on tuber lightly to crack the coating; there is no need to remove it completely.
Store the tubers layered with dry sawdust or peat in perforated plastic bags, if the cellar is warm, or if the tubers are kept at room temperatures.
If you intend to store tubers in warm and humid conditions, they are best coated in paraphine. Washed and dried tubers are dipped in the melted paraphine. After the coating sets on the tubers, the procedure should be repeated. Tubers with the paraphine coating should be stored layered with sawdust or peat in plastic bags. Knock on the tubers lightly to crack the paraphine coating prior to planting.
