Tuberous Begonias Begonia

Begoniaceae is a large flowering plant family with about 1500 different species and hundreds of hybrids. Mature begonia plants range in size from a few inches high to over 12 feet high and the flowers, foliage colors and sizes are very diverse. Most have fleshy stems. Some produce underground tubers or rhizomes. The American Begonia Society divides begonias into 7 informal groups by growth habit: cane-like, rex-cultorum, rhizomatous, semperflorens, tuberous, trailing or scandent, thick-stemmed and shrub-like.

The Rex-cultorum Group, commonly called Rex begonias, are usually rhizomatous and can vary in size and habit. They are grown primarily for their showy foliage. The leaves come in every color, pattern and shade, and every size and shape. Rex begonias are typically planted outdoors in mild climates as an annual summer bulb; alternatively, they can be grown as perennials in containers and brought indoors during the winter. Technically, Begonia spp. is an organ called an enlarged hypocotyl and it has hardiness of Tender III- injured below 25 degrees F (2 degrees C). Rex begonia needs morning sun to partial shade and, while it will tolerate full sun, it prefers sun dappled part shade and a good mulch in hot summer climates. It will tolerate considerable shade, but the result will be a more open form and fewer blooms. When grown outdoors, set plants out after last frost and space the plants 9 to 12 inches (22-30 cm) apart. When grown in containers and placed indoors, plants may be cut back in fall and overwintered in a cool location with reduced watering..

This plant needs bright indirect light year-round and humid conditions (though direct misting of the foliage encourages powdery mildew).  They need consistent water, but do not tolerate overwatering. Allow soils to dry between watering. They can tolerate less light than other begonias and will do well under fluorescents. It propagates easily by division through its knobby rhizomatous roots.

Diseases, Insects, and Other Plant Problems:

Susceptible to bacterial leaf spot, powdery mildew, botrytis, and stem rot, especially in humid conditions with poor air circulation. Watch for mealybugs and thrips.

VIDEO Created by Elisabeth Meyer for "Annuals, Perennials, Vines, and Groundcovers" a plant identification course offered in partnership with Longwood Gardens.