The begonia offers a remarkable array of plants to indoor and outdoor gardeners. Begonias are tropical perennials but fill trays in annual sections of garden centers each spring. The humble Begonia cucullata variety of wax begonia has been listed as an invasive in Hawaii and the Indian Ocean island of La Reunion by the Invasive Species Specialist Group of the Global Invasive Species Program.
Begonias are a large and varied family of tropical perennials native to Central and South America, parts of Africa and Southeast Asia. They grow as herbs, shrubs or vines with fleshy heart-shaped leaves that may be colored in shades of red or purple or brightly variegated in plants that are 8 inches to 2 feet in height. Begonias flower in shades of pink, white, red, orange or yellow in groups on short stems and may be small and simple or large camellia-type blooms.
The Begonia Society of the Palm Beaches says that the Chinese grew the Begonia grandis variety as early as 1400 and introduced them to Japan in 1641. Western horticulturists grew B. minor in the Kew Gardens in Britain in 1777, and begonias were growing in America by 1850. Today, B. grandis grows as a perennial in the southern U.S., and Rex begonias are grown primarily for foliage; wax begonias are a favorite bedding plant, and tuberous begonias are grown as specimens.
True to their tropical background, begonias prefer well-drained, slightly acid soil that is moist and fertile. All begonias grow best in dappled shade, although they will tolerate some early morning or late afternoon sun. Tuberous begonias can be dug up and stored over the winter like cannas or gloxinia; Rex and Reiger begonias are often grown indoors.
Growers propagate tuberous begonias by root cuttings; tubers will not divide reliably. Most begonias can be grown from seed, although planting must start indoors as early as December for summer bloom. According to the University of Minnesota Extension, germination of tuberous begonia seeds takes between 10 and 21 days at a constant soil temperature above 70 degrees.
Begonias are versatile plants; varieties are adaptable for bedding, containers or indoor gardens. They grow very slowly and make reliable, attractive bedding plants in shady areas. Bronze-leaved varieties will tolerate full sun better than others, according to Clemson University Extension.
Begonias will rot if allowed to stand in water or if planted in clay-heavy soil that holds water. Begonias may be affected by xanthomonas leaf spot, botrytis blight, pythium root rot and southern blight. University of Florida recommends that plants displaying disease symptoms be removed and discarded so that other plants are not affected.