Plant Profile: Begonia

The Begoniaceae family is a vast group of flowering plants, encompassing around 1,500 species and numerous hybrids. These mature begonias can vary significantly in height, ranging from just a few inches to over 12 feet, and they exhibit a wide array of flower and leaf colors, sizes, and shapes. Most begonias feature fleshy stems, with some varieties developing underground tubers or rhizomes. The American Begonia Society categorizes these plants into seven informal groups based on their growth habits: cane-like, rex-cultorum, rhizomatous, semperflorens, tuberous, trailing or scandent, and thick-stemmed or shrub-like.

Among these, the Rex-cultorum Group, often referred to as Rex begonias, is primarily valued for its striking foliage. These plants, which are typically rhizomatous, come in a variety of sizes and growth habits. Rex begonias are usually cultivated outdoors in temperate climates as annual summer bulbs, but they can also be grown as perennials in pots and brought indoors during colder months. The scientific classification of Begonia spp. refers to an enlarged hypocotyl, and these plants are classified as Tender III, meaning they can be damaged when temperatures drop below 25°F (2°C). Rex begonias thrive in morning sun to partial shade; while they can endure full sun, they prefer dappled shade and benefit from a good layer of mulch in hot summer conditions. Although they can survive in considerable shade, this may lead to a more open growth form and fewer flowers. When planting outdoors, it is advisable to wait until after the last frost and space the plants 9 to 12 inches (22-30 cm) apart. For indoor cultivation, plants can be pruned back in the fall and kept in a cool area with reduced watering during the winter months.

These begonias require bright, indirect light throughout the year and thrive in humid environments, although direct misting of the leaves can lead to powdery mildew. They need consistent moisture but should not be overwatered; allowing the soil to dry out between waterings is essential. Rex begonias can tolerate lower light levels compared to other types and can thrive under fluorescent lighting. They propagate easily through division of their knobby rhizomatous roots.

**Diseases, Insects, and Other Plant Issues:**
Rex begonias are prone to several issues, including bacterial leaf spot, powdery mildew, botrytis, and stem rot, particularly in humid conditions with inadequate air circulation. It's important to monitor for pests such as mealybugs and thrips.