THE NEED FOR WINTER STORAGE
Dahlia tubers are very cold sensitive and will need to be dug and stored in a cool but frost free storage area during the winter months. Fortunately, there are many acceptable storage methods for over wintering dahlia tubers. If you are new to dahlia growing or if your method is not working or easy enough you may wish to try this relatively new, but well tested, method that uses Saran wrap or any other plastic wrap film that is readily available from your local supermarket.
Storage of dahlia tubers using plastic wrap meets the primary goal of preserving the tubers in as close to as when dug condition. This method uses no additional storage medium such as the traditional vermiculite, peat moss, wood shavings or sand. The thin plastic wrap used in this method does provide for some air exchange but not to the extent that will allow the bulb to desiccate.
This method of storage does not require any changes in the digging, washing and dividing of your dahlia tubers.
Cut surfaces on freshly divided tubers heal over rather quickly after surface drying. The cut surfaces are a logical entry point for bacteria and fungi spores so it is recommended to use either a liquid fungicide such as Daconil or a powdered fungicide such as Captan. Garden sulfur flour is highly effective and very inexpensive. If you decide to use Daconil or Captan, you should follow the directions for use as provided by the manufacturer. If you should use sulfur flour it is recommended that you add ½ cup of sulfur to 4 cups of coarse peat, vermiculite or dry play sand in a medium sized plastic bag. A plastic shopping bag will work nicely. The divided dahlia tubers can be placed in the plastic bag and gently mixed so as to cover the tuber with a thin layer of sulfur flour. Care should be exercised so as to not breath the dust of Captan, sulfur flour or vermiculite (which can contains asbestos fibers).
Small quantities of tubers can have their cut surfaces disinfected using Lysol spray, a product that has been shown to provide excellent protection from spoilage caused by bacteria and fungal contamination.
Treated tubers will be ready for plastic wrap storage as soon as the surface of the tuber has dried, generally within several hours. Tubers that are not packed promptly will begin to desiccate resulting in lowered tuber quality and greater loss over the winter months.
The plastic wrap storage method is highly effective for small tubers and tubers with long, thin necks. These types of tubers frequently tend to rot or dry out with other storage methods.
PLASTIC WRAP YOUR TUBERS
Cut off a length of plastic wrap about 50 cm (two feet) in length and lay it flat on a counter or table surface. At one end of the plastic wrap place one of the tubers. Roll the tuber so that it is completely covered with a single layer of plastic. Then add another tuber and roll over one complete turn. Continue in this manner until you have rolled 5 or six tubers into a neat bundle being careful so that no two tubers are touching and to cover both ends of the tubers with the plastic wrap. Be certain that no tuber is touching another as plastic wrap should separate each tuber. Masking tape can be used to hold the plastic film in place. The name of each variety can be written on the masking tape with a permanent pen for easy identification.
Extra long tubers may need to be wrapped with the tuber parallel to the edge of the wrap so as to cover the entire length of the tuber. This is especially important when the tuber length is close to the width of the plastic wrap.
Wrapped and marked bundles of tubers should be stored in a storage container such as a corrugated box or bulb crate for the duration of the storage period at a temperature as close to 4 - 8 degrees C (40 – 46 degrees F) as possible. Tubers should not be stored in airtight containers as some air circulation is necessary.
SPRING PLANTING OF DAHLIAS
Upon examination in the spring you should find greater than 90% of your plastic wrapped tubers to be very firm and free of any spoilage. When it is time to plant or pot your tubers you can open the package, remove the tubers and check for “eyes” (where new growth will occur). Blind tubers, those without eyes, seldom produce new growth.
Plant your dahlias in the spring after the last possible frost.