Tuberous begonias are natives of South Africa and South America. A favorite to include in hanging pots and planters, they provide blooms all summer long in white, red, pink, yellow, orange and salmon in double or single blossoms that are often ruffled. The thick stems and large glossy leaves are signatures of this summer bulb. Properly overwintered, they can be kept for years, and with a little effort, propagated to produce more plants.
This summer bulb prefers moist, well-drained soil whether in a pot or garden bed; they are not drought tolerant. The plants prefer morning and afternoon sun and dappled sunlight at midday. Tuberous begonias do well set in pots, hanging pots or planters on porches, patios and decks or as a bedding plant for a cluster of showy blooms around other perennials with shorter bloom seasons. They require frequent fertilization with a diluted fertilizer solution for the best flowers and maximum growth.
Tuberous begonias are half-hardy perennials that can survive a light frost. In climates where temperatures fall below freezing, the dormant bulbs must be stored indoors. Beginning in late summer and early fall, watering of the plants should be reduced and the blooms removed to encourage food storage and dormancy. The tubers are lifted and allowed to dry in cool, dark area. Storing them over the winter in a perforated plastic bag filled with peat moss or vermiculite at 50 degrees Fahrenheit is ideal.
The earliest blossoms can be obtained by breaking dormancy in mid to late winter. The tubers are put in flats or pots, watered and put in a warmer location. After about a month, buds begin to appear in the hollow of the tuber and rootlets are forming on the bottom. The plants are moved to either a permanent location or to temporary pots to grow further and receive additional sunlight. Pinching the growing stems causes the plant to make branches, giving a bushier plant. Once the soil has warmed, plants can be moved to a bed or given a permanent home in a patio pot.
There are two main methods of propagation for tuberous begonias: stem cuttings and sowing from seed. Seeds sown in early winter indoors will produce plants that flower in June or July. Stem cuttings are placed in moist vermiculite until they begin to form roots. Transferring the rooted cuttings to larger pots or to a summer bed to grow allows them to form small tubers, which can be kept over winter to use the following year. The size of the original bulb determines how many cuttings may be taken.
Numerous forms of the plant include upright, bushy and trailing. Large plants may reach 12 to 15 inches in height and width. The tuberous begonia is a tropical plant but prefers a somewhat cooler climate. In summers where it is hot, protection from the sun is needed. Often sold as a part shade/shade-tolerant plant, this summer bulb requires bright, indirect sunlight for best growth. The preferred growing temperature for this plant is 70 degrees Fahrenheit, but it does well in warmer climates given adequate water, protection from the wind and some direct sun early or late in the day.