Tuberous begonias are popular for their vibrant, continuous blooms throughout the summer, but they originate from subtropical and tropical regions, making them highly sensitive to cold temperatures. These plants form an underground storage organ, the tuber, which allows them to survive adverse conditions by entering a period of winter dormancy. Since the tubers cannot survive freezing ground, they must be lifted and stored indoors each fall to ensure they can be replanted and flourish the following spring.
Preparing the Tubers for Winter Dormancy
Preparation begins in the garden as summer ends, guided by the plant’s natural cycle. In late summer, reducing the frequency of watering signals the approaching dormant period. This encourages the plant to draw nutrients from its foliage back into the tuber, a process known as ripening.
The ideal time for lifting is when the foliage naturally begins to yellow and die back or immediately following the first light frost. A light frost is preferred over a hard freeze, as a hard freeze can damage the tuber itself. Cut the stems back, leaving a stub of about four to six inches above the soil line. Wait a few days after cutting before removing the tubers, allowing the cut end to begin sealing over.
Curing and Cleaning After Lifting
Once the plant is ready, carefully lift the entire tuber and root ball from the soil, taking care not to damage the tuber. The tuber’s skin must be allowed to harden through a process called curing. After lifting, do not wash the tubers; instead, gently brush away any large clumps of loose soil.
Place the tubers in a single layer in a warm, dry, and well-ventilated location away from direct sunlight, such as a garage or shed. Allow them to cure for one to two weeks at 65–70°F, or until the remaining stem stub easily detaches. Curing allows the outer layer to suberize, forming a protective barrier that prevents moisture loss and entry points for fungal pathogens. Before final storage, remove any dried soil or small roots, and applying a fungicidal dust or sulfur powder can help minimize the risk of storage rot.
Choosing the Right Storage Environment and Medium
The storage location must maintain a consistently cool temperature, ideally between 40 to 50°F (4 to 10°C), while remaining completely frost-free. Temperatures that are too warm can cause the tuber to break dormancy too early, while freezing temperatures will destroy the plant tissue. The storage environment should also be dark and offer moderate humidity to prevent excessive moisture loss without promoting mold growth.
Tubers are best stored in a breathable container, such as a cardboard box, paper bag, or shallow tray, which allows for air circulation. The storage medium should be dry and slightly insulating to protect the tubers from temperature fluctuations and desiccation.
Materials like:
- Peat moss
- Vermiculite
- Perlite
- Sawdust
are excellent choices, as they absorb minimal moisture and help regulate the micro-environment around the tuber. Place a layer of the medium in the container, set the tubers on top, ensuring they do not touch each other, and cover them completely with more medium.
Monitoring Tubers During Dormancy
Throughout the winter, check the stored tubers periodically, ideally once a month, to ensure their health. The primary issues to look for are signs of desiccation or fungal infection.
If a tuber appears shriveled or feels soft and wrinkled, it indicates too much moisture has been lost. In this case, lightly misting the storage medium, not the tuber itself, can reintroduce a small amount of humidity to the environment.
Conversely, any tubers showing signs of rot, such as soft spots or the presence of fuzzy mold, must be removed and discarded immediately. Fungal spores can spread rapidly in an enclosed space, threatening the entire collection. By late winter or early spring, the tubers will naturally begin to swell and may show small pink or white sprouts, signaling that the dormant period is ending and they are ready to be potted up for the next growing season.