How to Grow and Care for Rex Begonias

Among the various types of begonias, Begonia rex is one of the most beautiful and dramatic plants. Sometimes called painted-leaf begonias or fancy-leaf begonias, these plants are known for their variegated leaves. 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 and many growers pinch off blooms to maintain breathtaking leaf displays. If planting outdoors, do so in May after frosts, but plant anytime indoors. These plants have a moderate growth rate, which means they may grow to less than 12 inches in a year. The splashy rex begonia is toxic to animals.

Rex Begonia Care

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.

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, feed the plant regularly, and keep the plant moist, but avoid overwatering.

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.

Light

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.

Soil

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

Water

Rex begonias require regular water, but be careful not to overwater 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. But don't let the soil become overly dry or the plant will begin to wither. The soil should be watered to feel slightly, but evenly moist.

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.

Fertilizer

Use liquid fertilizer weekly at quarter strength or at half strength every two weeks.

Types of Rex Begonias

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 used to market the 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.

Propagating Rex Begonia

The vast majority of begonias offered in the trade are hybrids so they 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.

Potting and Repotting Rex Begonias

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.

Common Pests & Plant Diseases

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

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

Common Problems With Rex Begonias

You'll notice if the leaves of your lovely rex begonia begin to wilt, which is one of its most common problems. Besides a pest infestation, there may be other reasons why the leaves are wilting, including the following:

• The soil is too dry or too wet.
• The soil is not draining enough.
• The plant needs more light, but not intense light.
• The humidity levels are too low (but don't mist the plant because rex begonias do not like wet foliage).