A Question of the Week

Dhalia tubers

Dahlias can be kept for many years if they are treated properly. Dahlias start producing tubers in the spring, but these roots are not mature until late in the growing season. The longer they are kept in the ground, the more mature they will be, and chances are better they will survive in storage. Wait to dig up dahlia tubers until the top growth dies back or is killed by the first hard frost. Though the foliage may be dead, dahlia tubers will continue to develop for a time. Delay cutting dahlia stems until right before digging, because the stems are hollow and can collect water, which in turn promotes crown rot and tuber decay.

Use a garden fork or a spade to loosen the soil around the entire plant. The “neck” on dahlia tubers is relatively delicate and can be easily damaged while digging. Next, gently lift the tubers from the ground, being careful not to cut or skin them in the process. Any damage to the tubers allows disease organisms to enter, leading to rot and storage losses.

Next, clean the soil from the tubers. Swish them around in a tub of water or use a garden hose to wash away any clumps of soil. Soil contains microorganisms that can cause decay in storage, so it’s best to remove as much as possible. Tuber clumps can either be left intact for the winter and divided in the spring, or they can be divided in the fall. Some gardeners find that it is easier to divide in the fall, and divisions are more convenient to store. The dahlia tubers then need to be allowed to dry and cure. Place the dahlias in a well-ventilated area with a constant temperature between 60°F and 70°F and out of direct sunlight for a few days. Always remember to label your stored dahlias. A felt tipped pen can be used to write directly onto the tubers.

There are various ways to store dahlias over the winter, none of which is necessarily better than the others. Just make sure the tubers are kept chilled (below 50℉ but above freezing) and stored in a material that maintains moisture around the tubers but allows air flow. Once the tubers have cured, they should be packed in moistened vermiculite, wood shavings or sand. A little moisture goes a long way. If the storage medium is too wet, the tubers will likely rot. Place tubers inside plastic bags or cardboard boxes and then cover them with more storage medium before placing them in a cool storage spot. Remember to occasionally check on the dahlias over the winter. Remove any tubers that have started to rot before the decay spreads to healthy tubers.

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