Tuberous begonias are valued for their vibrant summer blooms, yet they are tender perennials that cannot survive freezing temperatures outdoors. Overwintering involves safely storing the dormant underground tubers during the cold months, ensuring the plant’s survival and rebloom in the subsequent season. This practice allows gardeners to enjoy the same mature plants year after year, often resulting in larger, more floriferous specimens. Preservation relies on timing and maintaining specific environmental conditions throughout the dormancy period.
When to Prepare Begonias for Dormancy
The timing for initiating the overwintering process is cued by the shift in the seasons. As daylight hours shorten and temperatures cool in the fall, the begonia begins to transfer energy from its foliage down to the tuber. It is beneficial to allow this process to continue for as long as possible before frost damage occurs.
The critical moment to act is immediately after the first light frost causes the leaves to blacken and soften. This event signals the plant to cease growth and enter a resting state, having completed the necessary energy translocation. At this point, the foliage should be cut back, leaving a short stem of four to six inches attached to the tuber. Delaying the process until the soil freezes, however, will destroy the tuber, so action must be taken quickly after this initial frost.
Lifting and Curing the Tubers
Once the stems are cut back, the next step involves carefully lifting the tuber from the soil. Using a garden fork to loosen the soil several inches away from the plant helps prevent accidental damage, as any wound can provide an entry point for rot in storage. Gently shake off the loose soil surrounding the tuber, but do not wash the tuber, as the added moisture increases the risk of fungal infection.
The tuber must then undergo a curing process to dry completely and prepare for storage. Lay the tubers out on a flat, shaded surface, like a screen or newspaper, in a cool, dry, and well-ventilated area for seven to fourteen days. Proper curing allows the remaining stem to dry and detach easily, and any minor scrapes to callus over, reducing the moisture content that leads to decay. After curing, any remnants of the stem and fine roots should be removed, and the remaining dry soil brushed away.
Maintaining Ideal Storage Conditions
The longest phase of overwintering requires maintaining a specific environment to keep the tubers dormant. The optimal storage temperature range is between 40°F and 50°F (4°C to 10°C), which is cool enough to prevent premature sprouting but safely above freezing. A cold cellar, unheated garage, or insulated shed that remains frost-free is typically suitable for this purpose.
The tubers should be stored in a medium that provides insulation and absorbs residual moisture. Recommended materials include dry peat moss, vermiculite, or sawdust, used to surround the tubers in a cardboard box or ventilated crate. It is important to pack the tubers so they do not touch one another, as this limits the spread of potential mold or rot.
Periodic monitoring is necessary throughout the winter dormancy. Checking the tubers for signs of shriveling indicates the storage medium is too dry, and a slight misting or addition of barely damp material is needed. Any sign of mold or softness means the area is too humid or the temperature is too high, requiring better ventilation or drier packing material.
Waking Up Tubers for Spring
The transition out of dormancy should begin in late winter or early spring, typically six to eight weeks before the last expected frost date. The stored tubers should be moved to a warmer location, maintaining a temperature around 60°F to 70°F (15°C to 21°C) to encourage sprouting. Look for the concave side of the tuber, as this is the top where the growth buds, or eyes, will emerge.
The tubers can be set in shallow trays or pots filled with a moist, well-draining potting mix, with the concave side facing up. The tuber should be barely covered with the mix and placed in an area that receives bright, indirect light. Watering should be minimal until new shoots and leaves are visible, preventing tuber rot during this initial phase of growth. Once the new growth is established, the plants can be gradually acclimated to outdoor conditions before being permanently moved outside after all danger of frost has passed.