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.
|Botanical Name||Begonia rex-cultorum|
|Common Names||Rex begonia|
|Plant Type||Herbaceous perennial|
|Mature Size||12 to 18 inches tall, similar spread|
|Sun Exposure||Part shade to full shade|
|Soil Type||Porous potting soil|
|Bloom Time||Not grown for flowers|
|Flower Color||Not grown for flowers|
|Hardiness Zones||10 to 12 (USDA)|
|Native Area||Parent species from Northeastern India, southern China, and Vietnam|
How to Grow Rex Begonia
Because these are primarily foliage plants, careful cultivation is important 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 that is cultivated for its beautiful foliage.
It can be challenging to find just the right conditions for rex begonia to display its best leaf color. Ideal daytime temperatures are around 70 degrees Fahrenheit, nighttime temperatures around 60 degrees, and a constant humidity level around 50 percent. Provide the plant with plenty of bright indirect sun, but keep it out of direct sunlight. Rotate the plant frequently to expose it to equal light on all sides.
Even the best specimen plant 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 plants from cuttings.
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 require regular water, but be careful not to over-water them. They thrive on humidity but be careful if misting leaves that they don't stay too wet and encourage powdery mildew. Let the soil surface become dry to the touch before watering.
Temperature and Humidity
Rex begonias do best in moderate temperatures (60 to 70 degrees Fahrenheit) and moderately high humidity (around 50 percent). Growth will slow in freezing temperatures and some types of begonias go into a dormant period during the winter due to lack of light. 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 at half strength every two weeks.
Potting and Repotting
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. If the rhizome still has room to grow in its pot, the begonia should be considered happily potted. When the rhizome begins to butt up against the sides of the pot, however, it's time to repot into a fresh pot with fresh soil. Divide the rhizome when repotting 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.
Propagating Rex Begonia
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. 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 to the bedding mix and making small incisions in the leaf veins or by inserting a leaf (with a petiole) directly into the soil. The petiole is the stalk that attaches the leaf blade to the plant stem.
Varieties of Rex Begonia
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.
Another interesting and beautiful begonia is B. masoniana, also known as the 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.
Rex begonias 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.
Powdery Mildew in Begonia. American Begonia Society.
Easy Houseplants - Begonias. University of Vermont Extension Department of Plant and Soil Science.
Rex Begonia. University of Connecticut Home and Garden Information Center.
Begonia. Texas A&M University AgriLife Extension Plant Disease Handbook.
Managine Pests in Gardens: Begonia—Begonia spp. University of California Agriculture and Natural Resources.