Rex begonias can be grown in the Mid-America window garden in warm, humid conditions in filtered sunlight.
They make the most brilliant and regal of foliage plants and should be known as the “King of the Begonias.”
The conditions under which a plant is found growing in its native clime are indicative of the requirements that must be substituted when the plant is domesticated.
Rex Begonia Origin
The first rex begonia was found in Assam, India, in 1858. There they were growing to perfection in a tropical region of dense forest. Heat and heavy rains made the air foggy with moisture.
These facts tell us that in our homes they must be kept moist, in a fibrous rich soil composed of leaf mold and made fast draining with the use of clean, sharp sand.
They grow best in diffused light in the window garden. They thrive under fluorescent lights with perhaps slightly less light than African violets require.
Characteristics of Rex Begonias
Rex begonias grow from a fleshy root-like tuber called a “rhizome.” This rhizome usually lies on the ground, and masses of small fibrous roots grow from it.
Some varieties are upright growers, and the rhizome grows vertically, making a plant that may be two to three feet tall.
However, the commonly grown varieties of rexes seldom become more than 18 inches tall.
The leaf stems are long, erect, very fleshy, and hairy. The foliage colors and variations are in countless combinations, and although Rex begonias are known for this colorful “plumage,” they also produce flowers. Sometimes, these are unshowy and may be borne beneath the foliage.
Other varieties produce flowers above the leaves that are very attractive and occasionally fragrant.
As an example, the variety ‘Curly Fireflush’ has dark green leaves edged in black, and the entire leaf is covered with red hairs. Its new leaves resemble red velvet, and the beautiful white flowers are very fragrant.
Humus Soil
Rexes should have a soil mixture firm enough to hold large plants yet porous enough for good drainage.
A medium of two-thirds leaf mold or rich compost and one-third sod soil with a few wood ashes and crushed charcoal makes a suitable mixture. Generally, soil that grows quality African violets should be satisfactory for rex begonias.
Good drainage is important. Place at least one inch of broken pottery in the bottom of the pot and cover it with sphagnum moss before filling the pot with the soil mixture. Keep moist but not drippy wet.
Use a well-balanced commercial fertilizer every two weeks, and follow the instructions given for house plants.
Feeding frequently but lightly is much better than an overdose. I have found that 1/4 teaspoon of nitrate of potash in a six-inch pot will produce strong leaves and beautiful blossoms.
Dormancy and Winter Care
Few rexes go dormant in the winter if proper care is given, but if one should drop its leaves, do not throw the plant away.
Set the plant aside and water just enough to keep the stem firm—once a week or every ten days.
When new growth starts, prune, keep the soil moist, and feed every two weeks. Most rexes bloom in the fall or early winter. The use of nitrate in potash through the winter will keep the leaves firm and prevent dropping.
Control Pests and Disease
Rexes are relatively free of disease and few pests attack them. This is because “bugs” do not like the high humidity and daily spraying that rexes require.
Should mealybugs, red spiders, thrip, or aphids attack plants, they can be dealt with by spraying with Malathion or by very light spraying from a house plant aerosol bomb.
If the plants are put outdoors in the summer, they must be in a very protected place that is cool and damp.
Such a place will harbor leaf-eating, slimy slugs. Poisons made specifically for these pests can be used to control them.
Cabbage or lettuce leaves scattered about in the evening will help. The slugs gather on the leaves and these can be destroyed in the morning.
Seeds Are Tiny
Rex begonias are easily grown from seeds. A small clear plastic seed tray with good drainage and damp screened sphagnum moss pressed down firmly is ideal for seed sowing.
Rex seeds are so tiny they appear to be rust-colored dust, and it is a miracle when they sprout so readily in about ten days.
Sprinkle the seeds thinly over the damp moss and do not cover them. Place the top on the tray and set it in a warm, dark place to germinate.
Germination and Seedling Care
Bottom heat will speed germination. After the little specks of green begin to appear, gradually remove the top of the seed tray and bring the plants into more light.
When the seedlings have four to six leaves, transplant them to a flat of leaf mold and sand.
Transplant the seedlings 2” inches apart, being careful not to damage the small roots when separating them. They may be left in the flat and fed every two weeks until they are three or four inches high and ready for three-inch pots. This will take three to four months.
New varieties and different leaf patterns result when two different rex begonias are crossed. After you have become a proficient grower of rex begonias, you will want to try your hand at cross-pollinating.
This is easily done on a bright, sunny morning when the pollen is ripe and when the yellow, twisted pistil becomes slightly moist with a sticky substance and is ready to receive the pollen. When the seed pod begins to turn brown, it is ripe and ready to be picked.
Put it in an open envelope or dish until it is completely dry and the seeds are ready to be tapped out of the papery seed pod.
Leaf Propagation
The leaves of rex begonias will root and produce more plants exactly like the one from which the leaf has been taken. Use mature, vigorous leaves from a healthy plant, keeping the stem intact.
On the underside of the leaf, at the junction of the veins, cut through the veins just below the lateral (V-shape), but do not cut clear through the leaf as this will cause it to rot.
Be sure to use a sharp knife that will not bruise the leaf. Place this leaf in a jar, propagating case, or plastic box filled with two inches of damp leaf mold, sand, peat moss, or vermiculite with the back of the leaf down.
Pin the leaf down with toothpicks, or hold it in place with pebbles. Do not cover the leaf with the rooting medium; cover the stem a quarter of an inch.
Keep moist, not wet, and place in a warm, shaded place. It will take from two to three months for roots and, subsequently, new plants to form. They are then divided and treated like young seedlings.
Propagation From Leaf Wedge Cuttings
Propagation is possible from leaf wedge cuttings. Trim mature leaves to three inches and cut between the large veins. Be careful to include a small portion of the main stem with each wedge.
Dip the wedge in a rooting hormone and set it 1/4-inch deep at an angle in the rooting medium. Small plants grow from the bottom of the wedge. Three to five wedges may be made from one large leaf.
Growing Conditions and Care
The culture of rex begonias differs slightly from that of more commonly grown begonias. Rexes will not tolerate wind or hot sun, and they do not like wet feet. They must have free air circulation.
They are heavy feeders and can be grown outdoors in the summer in the shade if sprayed twice a day. They will grow indoors in the greenhouse year-round, or in your living room—if enough humidity can be made available.
A glass or plastic case is a great aid in growing rex begonias in the house. Or they may be set on a tray of moist sand or gravel.
Indoor Cultivation and Lighting
If you have a table in a dark corner that could have a 48-inch fluorescent light unit placed over it, an ideal place should result in your rex begonias; they can also be grown in pots using the double pot method.
Line the large pot with damp sphagnum moss and set the small pot with your rex inside. Keep the moss damp, and your plant’s roots will not dry out.
Care For Upright Begonias
Upright rexes may be grown like an ordinary cane or angel wing begonias, but they require the same warm, humid conditions that regular rexes must have. Use bamboo cane stakes to keep the uprights in presentable condition.
Tie the branches loosely to the stakes with soft yarn, or use the commercial pieces of paper-covered soft wire for this tying.
Place the stakes and ties so they will not show from the outside, thus giving the plant a graceful, natural appearance.
Prune the plants in spring before new growth starts, leaving two nodes or leaves on each branch. This will give a compact plant with fresh, new growth.
Varieties of Rex Begonias For Commercial Growers
Hundreds of differently named varieties of rex begonias are available from commercial growers. A box of a dozen assorted, unnamed seedlings from a hybridizer can be had inexpensively.
Their leaf colorations will be different and exciting. It is wise to start with less expensive varieties.
They are usually the easiest to grow, and when you become a successful grower, you can try those plants that are more difficult.
44659 by Mrs. H. E. Dillard