Dahlias are tender perennials, meaning their fleshy, underground storage organs, called tubers, cannot withstand freezing temperatures. In climates where the ground freezes, tubers must be lifted and stored indoors for the winter to ensure survival and vigorous growth the following season. The high water content within the tubers makes them susceptible to damage and rot when exposed to prolonged cold. Proper winterization protects your investment and preserves your favorite dahlia varieties until spring.
Timing the Lift and Initial Preparation
The signal for lifting dahlia tubers is the first hard frost, which causes the foliage to blacken and collapse. This indicates the plant has ceased its growth cycle and starches are retreating into the tubers for dormancy. Waiting one to two weeks after the foliage dies back allows this process to complete, which is beneficial for successful storage.
Before digging, cut the main stalks down, leaving two to four inches of stem above the soil line. This short stem acts as a handle for lifting and prevents water from entering the hollow stem and causing crown rot. Use a garden fork or spade to gently loosen the soil in a wide circle around the plant, taking care to avoid piercing the tubers.
Carefully lift the entire clump by the remaining stem, shaking off excess soil. Attach a waterproof label to the stem of each clump to avoid mixing up varieties during storage. Place the whole clump upside down in a sheltered, frost-free location for a few hours so residual moisture can drain out.
Cleaning Curing and Dividing Tubers
Immediately after lifting, thoroughly clean the tubers to remove excess soil, which can harbor disease-causing organisms. Gently wash the clumps with a hose or in a large tub until the tubers and crown are clearly visible. This cleaning allows for inspection, where you should remove any tubers that are visibly damaged, mushy, or diseased.
After washing, the tubers require a short curing period to allow the outer skin to dry and toughen. Lay the clean clumps on newspaper or a wire rack in a cool, dark, and well-ventilated area for one to three days. Ensure they are protected from direct sunlight and freezing temperatures. This drying time helps seal minor abrasions, reducing the risk of infection during long-term storage.
While many growers store the entire clump and divide in the spring, dividing in the fall saves space and allows for the removal of non-viable parts. Each viable division must include a piece of the crown, or “neck,” with at least one visible eye or growth bud. Carefully cut the tubers apart, ensuring the delicate neck remains intact, as this is the connection point where new growth emerges.
Selecting the Storage Medium and Location
A successful storage environment requires maintaining a balance of temperature and humidity to keep the tubers dormant without rotting or shriveling. The ideal temperature range is cool but consistently above freezing, typically between 40 to 50 degrees Fahrenheit. Temperatures below 32 degrees will destroy the tubers, while temperatures above 50 degrees may cause premature sprouting.
To maintain moderate humidity and prevent drying out, tubers must be nested in a storage medium that retains moisture without being saturated. Materials such as peat moss, coarse vermiculite, or wood shavings work well; the material should be lightly moistened before use. Place the prepared tubers into a breathable container, such as a cardboard box or plastic tub with ventilation holes, layering the medium between the tubers so they do not touch.
The tubers should be checked periodically throughout the winter, perhaps once a month, for signs of distress. If the tubers appear shriveled or wrinkled, the storage medium is too dry and needs a light misting of water to reintroduce humidity. Conversely, if any tubers show signs of mold or rot, they must be removed immediately to prevent the spread of decay to healthy stock.