Tuberous begonias require a shady site with well-drained soil. They don't tolerate drought and are heavy feeders that need fertilization throughout the growing season. All tuberous begonias have a dormant stage, which requires them to be dug up, cured and stored during this period. Stored tubers are then replanted and started indoors in late winter or early spring.
Native to tropical South America and southern Africa, the tuberous begonia is known for its beautiful and colorful blossoms. The cultivars that are found in most garden centers are hybrids. They come in a variety of colors (red, orange, yellow, white, salmon and pink) and forms (single, double and ruffled). Some varieties have spots/blotches of a contrasting color, which, when planted, provides added interest in the garden bed. These lovely plants will blossom throughout the summer season. Tuberous begonias are used in container plantings, hanging baskets and in flower beds.
The shape of the tuber is disklike and its size increases as the plant grows. However, unlike other tubers, it doesn't form multiple tubers as it grows, meaning it doesn't need to be divided or separated at any time. Roots grow from the tuber surface. "Buds are found in the top center of the tuber near the stem base," according to Purdue University's Cooperative Extension Service.
Preparing the Tubers for Dormancy
Whether grown in the garden bed or a greenhouse, all tuberous begonias have a dormant period. When in their dormant stage, they should be stored indoors. Toward the end of August, slowly reduce watering and don't fertilize the plants as fertilizing encourages growth. You can also pinch off any flower buds during September as this will help the tuber to store energy.
Digging up the Tubers
The tubers should be dug up once the foliage begins to yellow or after a killing frost. Carefully lift the tuberous begonias out of the soil. Cut stems of the plants back to approximately 5 inches in length. You don't need to remove the soil or roots.
Curing the Tubers
Place the tubers indoors to dry/cure (they should be placed out of direct sun and at room temperature). Curing should take from two to three weeks (after curing, the stem pieces will feel dry and loose). Once the tubers are cured, remove the 5-inch stem piece. Do not wash the tubers, simply remove any stems, roots and soil from them. Examine the tubers for any rotting and remove any rotted spots. Tubers should then be dusted with a fungicide/bulb dust. (Bulb dust is a protectant.)
Storing the Tubers
Begonia tubers can be packed in a perforated plastic bag with either dry peat, sand, sawdust or vermiculite. The packing medium prevents moisture loss while tubers are in storage. Place tubers in a dark, cool area (between 40 to 50 degrees Fahrenheit) with low humidity. You might even consider placing them in a small refrigerator. Tubers should be checked for softening/rotting. Discard any rotting tubers.