Rex Begonia Plant Profile

Rex begonia (Begonia rex-cultorum) is a semi-tropical perennial plant normally grown as an outdoor container plant or houseplant. The forms sold commercially are carefully cultivated varieties of the B. rex species native to parts of eastern Asia. If planted in the garden (a relatively rare occurrence), rex begonia is grown as an annual in all but the warmest climates.

Among the various types of begonias, Begonia rex is one of the most beautiful and stunning plants. Sometimes called painted-leaf begonias or fancy-leaf begonias, these plants are known for their showy, sometimes jaw-dropping leaf coloration. They frequently have large leaves (up to 6 inches long) that are brightly colored in various shades of green, red, silver, and even purple. These plants are grown almost exclusively for their foliage—their blooms tend to be small and less showy, so many growers pinch off blooms to maintain breathtaking leaf displays. Some types of rex begonias go into dormancy during the winter.

Because these are primarily foliage plants, careful cultivation is a must to realize their full beauty. Use a porous potting mix in a relatively shallow pot, and feed the plant regularly. Keep the plant moist, but avoid overwatering. Be especially careful of directly spraying the leaves, as standing water will encourage powdery mildew, which is a disaster on a plant meant to be viewed.

It can be challenging to find just the right conditions for rex begonia to display its best leaf color. Ideally, give the plant daytime temperatures around 70 degrees Fahrenheit, nighttime temperatures around 60 degrees, and a constant humidity level around 50 percent. Give it plenty of bright indirect sun, but keep it out of direct sunlight, and rotate the plant frequently to give it equal light on all sides.

Even the best rex specimen can only be expected to thrive for a few years. But because they propagate so easily, it's a simple matter to keep a steady supply of healthy plants by creating new ones from cuttings every year.

Rex begonias like bright, indirect light year-round. Because they are not aggressive bloomers, they can tolerate less light than other begonias and will thrive under fluorescent lights.

Airy, light, fast-draining soil is best for rex begonias.

Rex begonias like regular water but hate being overwatered. They also thrive on humidity but don't like direct misting, which encourages powdery mildew. Let the surface of the soil get dry to the touch before watering.

Rex begonias like moderate temperatures (60 to 70 degrees Fahrenheit) and moderately high humidity (around 50 percent). They cannot tolerate freezing, and some types of rex begonias go into a dormant period during the fall. As with other begonias, the rex and other foliage begonias prefer the same humid, gentle environment in which understory ferns thrive.

Use liquid fertilizer weekly at quarter strength, or biweekly at half strength.

Rex begonias are rhizomatous plants that grow from a shallow and knobby rhizome. As such, they do best in large, relatively shallow pots where the rhizome has room to spread. As long as there is still room to grow in the pot, the begonia should be considered happily potted. When the rhizome begins to butt up against the pot side, however, it's time to repot into a fresh pot with fresh soil. Divide the rhizome at the potting time to increase your plant stock. As with all begonias, don't soak the soil of newly potted plants, but do keep it lightly moist and warm.

The vast majority of begonias offered in the trade are hybrids and thus cannot be accurately propagated from seed. Rhizomatous begonias such as the rex begonia can be easily propagated by rhizome division during repotting, while almost all begonia species will readily sprout from leaf-tip cuttings. A rooting hormone can help the cuttings sprout.

Rex begonias can also be propagated by pinning a leaf down to the bedding mix and making small incisions in the leaf veins or by inserting a leaf (with a petiole) directly into the soil.

Begonia rex is the basis for many hundreds of hybrids, and its forms are too numerous to count. The resulting hybrids are often known in the trade only by fancy trade names dreamed up by growers looking to market their plants. As a result, you might find that the same crosses have different names in different garden centers. One interesting and beautiful begonia that's often included with the rex begonias as a foliage begonia is the B. masoniana, or iron cross, begonia. This beautiful plant was introduced to cultivation in 1952 and has puckered leaves with a dark cross in the middle. It's available in various colors.

These plants are often troubled by mildew and botrytis fungal disease. A systemic fungicide can help. Remove dead leaves promptly and provide good air circulation.

Mealy bugs can also be an issue. To prevent them, keep the plant well-trimmed and remove dead leaves from the surface of the planting mix.