Missouri Botanical Garden Bulletin 4(6): 109-112 (1916)

TUBEROUS BEGONIAS

During the summer the tuberous begonia, with its large waxy flowers of various colors, has no equal for an indoor floral display, and the Garden will have a large collection on exhibit during the months of July and August.

The begonia was named after a French patron of botany, M. Begon, and the term "tuberous" is applied because the group possesses perennial rootstocks. Thirty-five years ago the plant was just beginning to attract popular attention. At that time a number of hybrid forms were introduced, and the evolution since then has resulted in the production of varieties with large-sized blossoms as double as a rose. At the present time nearly every imaginable tint is being shown, as well as many shapes which often present an extraordinary similarity to other flowers, such as camellia, rose, hollyhock, carnation, and peony. In a great many varieties the petals are round, in some short and narrow, while in others they are fine and frilled; sometimes they are loose and open and often the reverse is true. Many of the flowers are flat when open, a few are anemone-centered and others are globular, pyramidal, or elliptical. The plant blooms continuously from June to October, the duration of the individual flowers varying from three to six weeks from time of opening.

The first species concerned in the parentage of the present day forms was Begonia boliviensis, which was introduced into England from Bolivia in 1864. It is characterized by long narrow leaves and scarlet fuchsia-like flowers. This species has recently been crossed with some of the double and single forms and has given rise to a type with long pendulous stems and drooping flowers which is very suitable for hanging baskets.

The next species to be introduced was Begonia Pearci, also from Bolivia, in 1866. The plant has large yellow flowers in axillary panicles and has been the chief factor in the production of hundreds of yellow, buff, and orange forms. In 1867 B. rosaeflora was brought from Peru. It bears large rose-red flowers and has proved to be important in the creation of some of the white forms, the best known of these being the "Queen of the Whites." The same year B. Veitchii followed, with its round vermillion-tinted flowers, to which many of our present-day varieties owe their coloring. In 1876 B. Clarkei and B. Davisii were introduced. The former has rose-colored blossoms, and the latter, a dwarf plant with smooth glossy foliage, has been of great value to the hybridists who, by crossing it with other strains derived from B. boliviensis and B. Veitchii, have produced a number of varieties with a dwarf compact habit but moderate sized and highly colored flowers.

The above-named species are the chief parents of the present-day forms and in their native habitats grow at an altitude of 11,000 to 13,000 feet, which, however does not signify that they are hardy in our climate. It will be noticed that, with the exception of the yellow-flowered B. Pearci, all the original species have red, scarlet, or crimson flowers; yet the result of hybridizing and crossing has been the production of progeny showing many varieties of color, such as white, pink, yellow, orange, crimson, and many intermediate shades. Veitch & Sons of England, and when the small drooping flowers of the parents are compared with the large brilliant flowers of to-day, it seems hardly credible that such magnificent results could have been produced in a little over thirty years.

Cultivation.—The cultivation of the tuberous begonia is not difficult. The easiest way is to purchase the young tubers from a specialist and start them in February or March in shallow boxes filled with sandy loam. They should be placed far enough apart to prevent matting and tangling of the roots when taken up to be potted, and kept at a temperature of 60-65F. The plants are ready for potting when the new shoots are about two inches long. The soil should consist of sandy loam and well-rotted manure in proportion of four to one. The size of the pots should vary according to the tuber, but generally a three-inch size is large enough for the first potting. After potting watering should be moderate, as excessive moisture causes decay at the base. A light, airy house and a temperature of 55-60F. are necessary for the best development. However, when the flower buds begin to form it is advisable to apply shade to the glass. This not only improves the coloring of the flowers but also their keeping qualities.

By the first of June all the plants should be in their flowering pots. The amount of water given at this time should vary according to the weather and the growth. It is important, however, to water in the morning, for if the foliage is wet when the sun is powerful, brown blotches occur where the drops of moisture have rested. To produce fine bushy plants early flower buds should be inched off so that the strength will go to the plant itself, and the leading shoots should be removed to encourage side growths from lower down the stem. In order to bring forth showy specimens growth should be stimulated by feeding with liquid manure two or three times a week. The liquid manure may be made by suspending a half-bushel sack of cow manure in a 50-gallon barrel of water.

In October when signs of ripening begin to show, the water should be gradually withheld until the growths decay, and the pots then placed on their sides under the benches in a greenhouse at a temperature of 40F.; or the tubers may be taken out of the pots and placed in dry sand in a cool cellar. In either case, care must be taken to prevent any moisture from reaching the tubers during the resting period. In the spring, as soon as the tubers show signs of growth they should be potted, the best plants being produced during the second year, although they are good for several years.

Propagation.—Tuberous begonias are propagated by seeds, division of tubers or by cuttings of side shoots, the most common and satisfactory method being from seed. The seed should be sowed in shallow boxes or seed pans about February 1, the compost consisting of equal parts of leaf mold and peat and one-quarter charcoal. The seed are very minute, resembling tobacco dust, and for this reason are best sown directly on the surface of the soil. The pan should be covered with a glass pane and shaded to prevent drying out, but as soon as the seed germinate the glass and the shading should be removed. When the plants show the third leaf they should be pricked into flats containing a compost similar to the one mentioned above, and spaced two inches each way. It is advisable to keep the flats in a moist atmosphere, and near the glass of the greenhouses to prevent spindling. Later the plants should be transferred to four-inch pots using soil similar to that used for the tubers. The subsequent treatment corresponds to that of the tubers.

If it is desired to retain and increase the stock of any variety this may be done by taking cuttings of side shoots, two to three inches long, during the summer and inserting them into leaf mold sphagnum moss, or cocoanut fibre. The cuttings should be kept close and shaded for several days, a moist atmosphere maintained by sprinkling overhead, and the temperature kept at 60-65F. As soon as the cuttings root they should be potted.

Another method of increasing the stock of any desired variety is to cut large tubers into parts, each of which contains a bud. This should be done in the spring, and the treatment thereafter is similar to that for the tubers. A necessary precaution in this method is to dip the tubers into slaked lime or charcoal to hasten the healing of the cut.

Hybridization.—The raising of new varieties from seed is a most interesting occupation. The grower's enthusiasm is somewhat dampened at the start by the uncertainty of results, but the variety and brilliance of the flowers are hardly to be equalled by any other plant. The operation itself is simple. The female parent is chosen and the stamens are cut off before the pollen is ripe, and the flower enclosed in a small waxed paper bag to prevent any foreign pollen from settling on the stigma. The male flower may also be enclosed in a similar bag to avoid the intermixing of pollen from other plants by insects. As soon as the stigma of the female plant is ripe—which can be told by the protruding of little hairs upon it—the pollen of the male plant may be brought to it by means of a camel's-hair brush or forceps, this being best accomplished in the middle of a bright day. In a day or two the stigma will turn brown and gradually die away, thus indicating that fertilization has taken place. A pod, which is soon formed, bursts at the top when ripe, and the seeds fall to the bottom of it. Some difficulty is experienced with the double flowers. Very often these fail to produce pollen, as the pollen-bearing stamens may have changed into petals. This condition may be avoided, however, by starving the plant, that is, reducing the water supply, thus forcing the flowers to be smaller and sometimes changing them into single flowers with some pollen-bearing stamens. This procedure is not always successful, however.