1158 Begonia x tuberhybridaCommon Names: tuberous begonia Family: Begoniaceae (begonia Family)
There are some 1500 species of begonias and, by some estimates, more than ten thousand named cultivars and hybrids. To simplify matters, they are divided by horticulturists into informal groups, based mainly on their growth habits. Different authorities recognize different groups, but most use a system that looks something like this:
- Cane-stemmed begonias have woody, upright, straight, sometimes brittle stems and fibrous roots. These evergreen perennials are prized both for their colorful, often hanging, flower clusters and their showy leaves. The popular angel wing begonias are in this group.
- Shrub-like begonias have multiple stems and a rounded, bushy habit. These are evergreen perennials, usually cultivated for their interesting and colorful foliage, and often used as bedding plants.
- Rhizomatous begonias grow from thickened stems called rhizomes that may be under the soil surface, creeping along the surface, or even upright. This is a variable group, but most are evergreen perennials grown for their spring blooming flowers and their interesting leaves that come in many shapes, textures and colors. The old beefsteak begonia (B.'Erythrophylla') is one of these.
- Rex-cultorum begonias are derived from hybridization between B. rex and several other begonia species. Most have rhizomes and are evergreen, but some are tuberous and tend to go dormant in winter. These perennials are grown mainly for their striking foliage.
- Semperflorens begonias, perhaps the most widely grown type, are compact and bushy evergreens with soft, succulent stems and fibrous roots. Known as wax begonias (Begonia x semperflorens-cultorum) and often grown as annuals and bedding plants, they are nevertheless perennial. Wax begonias are hybrids derived from various South American species and grown for their flowers and their shiny green or bronze, sometimes felted, leaves.
- Winter-flowering begonias are small, compact evergreen perennials grown mainly for their profuse and colorful flowers, although some have beautiful leaves as well.
- Trailing begonias have pendant growth with beautiful displays of flowers, sometimes year-round. These are well suited for hanging baskets. Most trailing begonias have bright green leaves.
- Tuberous begonias are generally upright, bushy perennials that grow from underground tubers, flowering in summer and losing their leaves and going dormant in the winter. These are grown mainly for their flowers, which come in an astonishing diversity of textures, shapes and colors. Several subgroups (sometimes elevated to groups) of tuberous begonias can be recognized, including the Semi-tuberous group; the Pendula group of trailing varieties; the Multiflora group; and the most popular tuberous begonias, the Tuberhybrida group, which are hybrids of several Andean species.
Most tuberous begonias are upright and bushy in stature, but some are trailing, suitable for hanging basket cultivation. Tuberous begonias have sprays of flower clusters that consist of two small female flowers and one larger, showy, sometimes double, male flower that can be as small as 0.5 in (1.25 cm) across or as large as 10 in (25 cm) across. Flowers come in every color except blue, may be plain, frilly or ruffled, and some are even fragrant. The foliage and flowers are produced in summer from tubers that were dormant during the shorter days of winter.
The semi-tuberous begonias don't have a tuber but rather a swollen base called a caudex, from which numerous smaller stems emerge. Semi-tuberous begonias can look like little bonsai plants, reminiscent of a miniature baobab tree (Adansonia digitata).
Most tuberous begonias available in nurseries are members of the Tuberhybrida group. The botanists refer to them as Begonia x tuberhybrida. These are among the most beautiful of container plants. Many have spectacular flowers that look like large camellias or roses. Some are bicolored.
The many wild species of tuberous begonias occur naturally in the tropics and subtropics of Africa, Asia and Central and South America. Most tuberous begonias available in nurseries are hybrids of garden origin.
CultureTuberous begonias do best in a well drained, neutral to slightly acidic peat based potting mix. They need good air circulation to combat powdery mildew. Light: Most begonias, and the tuberous hybrids are no exception, thrive in bright, filtered light and do not like direct sun. Moisture: Tuberous begonias cannot tolerate waterlogged soil nor should they be allowed to dry out once growth has begun in spring. They need moderate watering during growth and flowering, but when they drop their leaves and stems in autumn the tubers must be kept dry. Hardiness: USDA Zones 9 - 11. Most begonias cannot survive frost or freezing temperatures. Two exceptions are the tuberous begonias known as hardy begonia (B. grandis subsp. evansiana) and the Peruvian B. octopetala, which can take temperatures down to 5°C (23°F) (Zone 6). Where frosts do occur, the tubers of all other tuberous begonias grown in the ground must be lifted when the foliage begins to die back following the first frost. The tubers are then stored until warm weather returns. Store dormant tubers at 41-45°F (5-7°C). Force tubers back into growth in spring at around 65°F (18°C). Optimum temperatures for growth and flowering are between 66 and 77°F (19-25°C), and higher for some of the more tropical species. Propagation: Propagate tuberous begonia plants from stem cuttings during growth or from new basal stems that can be detached when growth commences in spring. Some species, including hardy begonia (B. grandis) and hollyhock begonia (B. gracilis), produce little bulbils in the leaf axils that can be potted up. These should be placed on the surface of damp potting mix and submerged in the soil when growth begins.
Some tuberous begonias (especially those in the Tuberhybrida group) are used as bedding and border plants that must be lifted in autumn and kept dry during the winter if they are to see another summer. Unless new plants are to be sown each spring, the tubers should be dug up, dried, dusted with fungicide (flowers of sulfur is fine) and stored until spring when they are replanted, convex side down. Even when grown in warmer climates, tuberous begonias will go dormant as day lengths shorten in the fall, and they still need a dry winter resting period. For tuberous begonias grown in containers in the greenhouse or as house plants, water must be withheld during the winter dormant period, but the tubers may be left in their pots. (Tip the pot on its side.)
You can create larger flowers and prolong the flowering period of tuberous begonias by pinching out the two smaller female flowers that grow on either side of the male flower.
The trailing varieties of the Pendula group, with their showy red, pink, orange or yellow flowers, are excellent in hanging containers. Hardy begonia (B. grandis) can be left in the ground over winter. The ‘Non Stop’ hybrids are used as outdoor bedding plants, started from seed in spring, and flowering all summer. For these, so easily planted from seed, lifting the tubers in fall is scarcely worth the effort.
If you purchase tubers, keep them dry and around 41-45°F (5-7°C) until late winter or early spring and then bring them up to around 65°F (18°C). Wait until new growth appears before planting, rounded side down, about 1-2 in (2.5-5 cm) deep.
As befitting a group of such diversity, beauty and interest, there are many organizations devoted to the culture, appreciation and hybridization of begonias. Start with the American Begonia Society, which publishes a regular journal.
Love of begonias could become habit forming. There is talk of a Begonias Anonymous 12-step program for addicts.
Steve Christman 8/16/12