Rex begonia (Begonia rex-cultorum)

Overview

The Begonia rex-cultorum, commonly known as the Rex begonia, is prized almost exclusively for its spectacularly colored and textured foliage, making it a superstar in shaded interiorscapes. These rhizomatous perennials are widely hybridized, resulting in leaves displaying an incredible range of silver, red, green, and dark maroons, often with prominent veining. While technically herbaceous perennials, Begonia rex-cultorum is generally treated as a frost-tender annual outdoors in most climates, thriving best when grown as a houseplant. Cultivating successful Rex begonia requires mimicking its native humid, rocky valley environment, rewarding attentive gardeners with unparalleled tropical drama.

Fast Facts

• Plant Family: Begoniaceae
• Plant Type: Herbaceous perennial
• Hardiness Zones: USDA Zones 10-11
• Size at Maturity:
  • Height: 1-1.5 ft
  • Spread: 1-1.5 ft
• Bloom Time: Flowers not showy
• Sun Exposure: Part shade to full shade
• Water Needs: Medium
• Maintenance Level: High

How to Grow

When planting Begonia rex-cultorum, choose containers that are appropriately shallow, utilizing a very porous planting mix to prevent moisture retention against the rhizome. Since Rex begonia are frost tender, they must be brought indoors or treated as annuals when temperatures drop below viability. High humidity, ideally above 50%, is critical for these plants; dry air will severely stress the foliage.

Watering requires attention; allow the soil surface to become almost dry before watering thoroughly. Overwatering is a significant risk factor leading to common issues. Fertilization should be heavy during periods of active growth in spring and summer, using a balanced formula (like 23-19-14) applied at quarter strength every two weeks, or a controlled-release product applied quarterly. Reduce feeding significantly in fall and stop entirely in winter.

Lighting requirements demand plenty of bright, indirect light, but direct, hot sun must be avoided entirely as it scorches the leaves. If light enters predominantly from one direction, rotate the container weekly to ensure even growth. Optimal day temperatures are around 70°F with cooler nights near 60°F. If growth stalls in cooler winter months, the plant may enter dormancy; reduce watering significantly until new growth appears in spring.

Landscape Uses

As annuals or container specimens, Rex begonias provide unparalleled focal points in protected outdoor areas or indoors. They are ideal for adding rich, variegated color to shaded decks, covered patios, or balconies where they receive ambient light rather than direct sun. Because of their demanding environmental needs, they function best when placed near other humidity-loving tropical foliage plants, creating a lush, layered look in small spaces or rooftop gardens.

Standout Features

Flower Qualities

• Insignificant

Noteworthy Characteristics

Begonia rex-cultorum is a name applied to a group of cultivated begonias known as rex begonias. All rex begonias include the wild species B. Rex in their parentage. This rhizomatous perennial is native to rocky, forested valleys and slopes in northeastern India, southern China, and Vietnam. The leaves have are sparsely hairy, have prominent veins, and can reach up to 12” long and 8” wide. Rex begonias are widely hybridized and cultivated for their showy foliage.

Tolerances

• Black Walnut

Potential Problems

Rex begonias are susceptible to mildew and botrytis fungal infections, especially when humidity is too high without sufficient air movement. Mealy bugs can also be problematic, particularly when the plant is stressed or kept too dry. The most effective preventative measure is diligent grooming: promptly remove any dead or fallen leaves from the soil surface and ensure excellent air circulation around the plant. Treating issues early with appropriate systemic fungicides or horticultural oils is recommended if infestations persist.

Frequently Asked Questions

What hardiness zones is Rex begonia suitable for?

This plant is hardy in USDA Zones 10-11, meaning it requires protection or indoor status in cooler climates.

How large does Rex begonia grow?

The typical size at maturity for Begonia rex-cultorum is between 1 and 1.5 feet tall with a similar spread.

What sun exposure does Begonia rex-cultorum need?

This species requires part shade to full shade exposure; avoid intense afternoon sun which can damage the delicate leaves.

When does Rex begonia bloom?

The flowers of Begonia rex-cultorum are generally considered not showy.

Conclusion

The vivid, painterly foliage of the Begonia rex-cultorum makes it an unforgettable addition to any collection, whether sited indoors or outdoors during warm weather. Mastering the precise requirements for humidity, light, and water elevates the care level of this Rex begonia, but the visual payoff is exceptional. Before planting, assess your growing environment to ensure you can meet the high humidity and consistent temperatures required for this stunning tropical perennial.

Propagation Tips

Propagation of Begonia rex-cultorum is typically done through division of the rhizome or by leaf cuttings, though the latter is more challenging. When pruning upright cultivars or managing an overly long rhizome, cut the desired section, ensuring the piece contains at least one node. Treat the parent plant as usual and plant the rhizome cutting shallowly in a porous, slightly damp medium. Be patient, as new leaf development from rhizome cuttings can take time, but this is an excellent way to multiply your collection of this dramatic foliage plant.

Seasonal Care Calendar

For indoor growers, the growing season is dictated by light availability, but generally begins in spring when new growth emerges. This is the time to begin regular, diluted fertilization (every two weeks) and ensure humidity levels are maintained above 50%. If you move your Rex begonia outdoors for the summer, do so gradually to acclimate it to brighter (though still indirect) light. In fall and winter, observe the plant for signs of dormancy; if leaf drop occurs, significantly reduce watering frequency until spring signals the return of active growth.