Digging and Storing of Dahlias Tubers
By Bob Preuss
When to Dig: After the first killing frost the stalks are cut to about 4” above the ground. In our region, this normally occurs in mid to late October. This is not to say that the process requires a killing frost before digging should we have an unusually warm fall. Once the plant material and stakes have been removed from the garden, the roots may be left in the ground for several weeks to mature and form eyes which makes dividing the root clumps easier. Roots lifted prematurely tend to shrivel and dry out during storage, ultimately leading to their loss. There is no exact time for lifting the root clumps, but generally speaking, most growers dig their roots after the 15th of October and before the cold days of November. Should the weather turn extremely cold with danger of the ground freezing, dig your roots immediately as frozen roots will not survive!!!! Use large garden shears or a small saw to cut the stalk as they are sometimes large and very hard. Attach labels to each stalk before digging to retain the variety name during winter storage.
Digging: Using a shovel or garden fork, carefully dig around the plant approximately 12 inches from the main stalk. Gently lift the root clump from the ground with the shovel or fork, loosening the soil surrounding the clump by tapping the stalk. Most of the soil will dislodge from the clump during this process and the clump safely lifted from the ground without damaging individual tubers. The next step is to spray the clump with water to remove any remaining dirt. This is best accomplished by placing the clump inside a garden tray or on the top of a milk crate to provide support for the tubers and avoid damage. At this point let your clumps air dry for 1-2 hours to harden the skin before proceeding to the dividing step. Keep in mind that each individual tuber is attached to the crown (base of the main stalk) and the tuber neck can be damaged during the digging or handling of the clump before division.
Dividing: The dahlia clump can be divided into individual tubers after digging or stored as a clump and divided in the spring. Seasoned growers will lobby for both methods, but the clumps are easiest to divide in the fall when they are soft and spring is a busy time of the year! After the clumps have been washed and air dried, the clumps can be divided into individual tubers. This process can be done over several days, but avoid leaving your clumps on the bench for weeks before dividing as they tend to dry out and shrivel. When you start your root-dividing, look for eyes (growth buds) on the crown (center of the root clump below the stalk). The mother tuber (root planted in the spring) will be easy to identify and should be discarded. The next step is to divide the clump in half and select the tubers for storage. Support the clump on a wooden block and cut through the main root clump with a sharp knife dividing the clump into two halves. Keep in mind that the growing eyes for next year come from that portion of the crown attached to the tuber and not the tuber body. Once you have selected the best tubers to save, continue dividing the clump into sections, saving a portion of the crown, which has an eye with each tuber. If no growing eyes are visible, save as much of the crown with each tuber as possible. The eyes sometimes develop during winter storage or when planted in the spring.
Storage: Tuber storage is another area where there are several methods that work equally well and seasoned growers will again lobby for each method. One method is to store your divided tubers in coarse vermiculite. Gallon size freezer bags work very well for storage and can easily be labeled to retain identification. Vegetable bags with thousands of tiny vent holes work extremely well, but are difficult to purchase lately. Fill half of the bag with vermiculite, puncture the bag to make numerous vent holes and position the tubers inside. Many tubers can be stored in each bag depending on the tuber size. The main purpose of the vermiculite is to prevent the tubers from drying out too fast and retain some moisture during the storage process. Excessive moisture might lead to mildew and the rotting of the tubers. Pack the storage bags in containers with a few vent holes near the top of each container. Size the container to the volume of tubers and allow some free air space (10-20%) in each container. A few layers of newspaper on top of the storage bags inside the container will help control the moisture level. The ideal storage temperature is between 40-50 degrees (freezing temperatures will kill your roots!!!!). Wet tubers do not store well and increase the chance of rotting during winter storage. Make sure you allow the tuber to air dry and the skin to cure (harden) before storage. This short curing process slows down the moisture loss from each tuber during storage. Don’t forget to label each bag with the variety name! Individual tubers can be labeled with indelible pencils before storage or with black “Sharpies” in the spring when the tuber skin is dry and firm. The storage of dahlia tubers is not an exact science and it is not uncommon for new growers to lose their roots the first year! Check your tubers each month for mildew and rot! Experiment and find a method that works well for your storage conditions! Root cellars provide the optimum conditions for wintering dahlia tubers….good luck!
Note: When the dahlia roots are divided from the clump, each tuber must have a portion of the crown with a potential growth bud (eye).