Begonia rex was discovered in the Indian state of Assam, and introduced into culture in the middle of the XIX century. It is a herbaceous shrubby plant with a lodging pubescent shortened stem. The leaves are asymmetrical, heart-shaped, up to 30 cm long and 20 cm wide, greenish-brown above, with a broad silvery stripe. The petioles are pubescent, up to 10-20 cm long. Small white-pink flowers are collected in tassel-shaped inflorescences.
The rex group of begonias was first mentioned in print by the American botanist and horticulturist L.H. Bailey in 1920. Crossing the royal begonia with other species has achieved a wide palette of color combinations in the color of the leaf. The first hybrids were obtained with other Asian species, such as begonia yellow (B. xanthine),Griffith’s begonia (B. griffithiana), and begonia hatacoa, or red-nervous (B. hatacoa sin. B. rubro-venia). When crossing with the tuber begonia large (B. grandis), more hardy varieties with a vertical growth form are bred.
The introduction of the genes of the imperial begonia (B. imperialis) yielded varieties with smaller leaf sizes. Crossing with caudex begonias (semi-tuberous) made it possible to obtain miniature varieties of the Rex group. The red metallic sheen of the leaves, which is closely associated with rex-begonias, brought interbreeding with Begonia decora.
Begonia rex can grow well in places too dark for other begonias. Some will put up with the shadow, others need a well-lit place to reveal all their beauty. It is advisable to still provide begonias with good light, avoiding direct sunlight. Depending on the illumination, the color of the leaf changes. Some varieties are more strongly colored in the shade, others – in intense lighting. If the plant does not show the characteristic color of the leaf for the variety, try to rearrange it in a new place.
Turn the pot with the plant regularly relative to the incident light – about a quarter of a turn weekly.
The optimal temperature for the growth of Begonia rex lies in the range from +18 to +22°C. Begonias do not tolerate heat well. It is also undesirable to reduce the temperature below +16°C, with a cooler content, growth slows down. Plants do not tolerate sub-zero temperatures, so they should be protected from frost!
Begonia rex require high humidity, more than 50%, and some varieties up to 80%. Begonias with severe pubescence are afraid of water getting on the leaves. To increase humidity, spray the air next to the plant from a fine sprayer several times a day.
Soil and planting
Begonia rex are more fastidious to the composition of the soil than vertically growing varieties. They have small roots, and fleshy Begonia rex are in constant contact with the surface of the soil, and therefore can easily rot if it is too wet. Begonias need loose, well-drained soil. Add about 1/3 of the volume of perlite to the finished universal substrate. Many varieties can be grown as epiphytes in a small amount of loose soil covered with sphagnum moss. Most Begonia rex grows well in small and shallow plastic and clay pots or baskets.
When transplanting, place the rhizome at the same level or slightly deeper and shift to the edge of the pot with the old part of the rhizome to give more room to the growing crown.
Begonias are afraid of waterlogging. Between watering, the soil from above should become almost dry to the touch. In autumn and winter, many varieties stop growing and may lose some of the leaves, for them, respectively, watering is reduced. Try not to wet the leaves during watering, or water in the morning so that by night the water has time to dry.
is carried out from spring to autumn with a balanced complex universal fertilizer in 1/4 of the dosage, in autumn and winter fertilizers are not applied.
Cropping and shaping
Most varieties of rhizomatous and Rex begonias do not need pinching or pruning unless they are growing upwards. But over time, the rhizome can become exposed, which will spoil the decorative appearance of the plant. Pruning will promote branching, and the cut crown can be rooted. Most varieties of Begonia rex bloom in the spring, and if flowering is desirable, then all pruning and pinching should be postponed for the period after the end of flowering. In Begonia Rex, the inflorescence should be removed immediately after its appearance, and you can form it at any time. Old bad leaves should be removed with the petiole, carefully breaking it from the rhizome.
Diseases and pest
Of the pests, the mealybug is most often found, it can be quite difficult to detect on Begonia rex. Begonias are also affected by thrips and aphids, they can be suspected by the deformations of young leaves.
Begonia rex, as a rule, are covered with hairs and stipules, on the petioles and leaf plates there is also pubescence, these are convenient places for the accumulation of pests. If there is a need to use an insecticide, then preference should be given to systemic drugs, it is absorbed into the cell juice of the plant and acts from the inside, thereby destroying parasites in hard-to-reach places for spraying.
The most common disease is gray rot (botrytis). It appears as large rotten spots on the leaves, which are later covered with a gray cannon. The occurrence of the disease contributes to coolness and high humidity. When watering, try not to get on the leaves, do not water too often, letting the top layer of soil dry out between waterings. Diseased leaves should be removed, in severe cases treated with fungicides from gray rot.
For some varieties, powdery mildew can be a big problem, manifesting itself in the form of pubescent large white spots on the upper side of the leaf. If they are found, treat with powdery mildew fungicides.
To obtain new cultivars, different varieties are artificially pollinated, the resulting seeds are sown and the most promising ones are selected in the future.
Begonia rex can be propagated by both leaf and stem (rhizomatous) cuttings.
Growing a plant from leaf cuttings takes much longer than rooting a stem cutting. But this is a more gentle method of reproduction, in which minimal damage is caused to the mother plant. Choose a strong healthy leaf and cut with a clean tool along with a piece of petiole about 3-5 cm long Leaves can be cut into parts in the form of wedges, each of which should contain the main vein and a small part of the petiole. Or on the leaf plate across the veins at a distance of 2-3 cm, make several incisions and then place the leaf in the greenhouse on the prepared wet substrate with the back side down so that the incisions come into contact with the soil. You can cut the leaf into squares of about 2 cm, so that a vein passes through the center of each, and vertically dig them a little into the ground.
In the greenhouse, maintain high humidity by spraying if necessary, but not bringing to dampness. To prevent decay, it is advisable to treat the leaves with a fungicide. The greenhouse is hermetically sealed with glass or a transparent film and placed in a warm and bright place. After about a month, roots appear and then leave. After the appearance of young plants, they should be gradually accustomed to the open air, increasing the time of ventilation of the greenhouse.
As a substrate for rooting, you can use the soil for growing begonias or prepare a mixture of ready-made peat soil with the addition of perlite. For rooting leaf fragments where the probability of decay is higher, it is preferable to use pure perlite without the addition of peat substrate.
Another method of propagation by leaf cuttings is to simply put the leaf with the petiole in a jar of water. After some time, young plants will grow on it, although their number will be much less.
Begonia rex can be propagated with stem cuttings, cutting into parts long Begonia rex, sometimes already having their own roots, and tightly put on the prepared substrate. The growth of young shoots will be faster if you place such cuttings in a greenhouse.