There are more than 1,500 species of begonias (Begonia spp.) and more than 10,000 hybrids and cultivars. For practical purposes they are divided into three major groups; fibrous rooted, rhizomatous and tuberous. Most are tropical perennials and some will grow quite large in their native habitat. Begonias are reliably hardy only in U.S. Department of Agriculture plant hardiness zones 10 and 11. They are grown as houseplants or annuals in temperate climates. As houseplants their size may be limited by pot size, and in temperate gardens their size may be limited by the shorter growing season.
Fiberous Rooted Begonias
Fibrous rooted cane type begonias, including "Angel Wing," can grow 2 to 12 feet tall. They are generally heavy bloomers and some are ever-blooming. Shrub begonias, including wax begonias, are also fibrous rooted. Wax or semperflorens begonias are shrub begonias but are generally grown as annual bedding plants. In mild winter climates they can grow for years if they are left in place. Shrub begonias can range from miniatures that grow about 6 inches tall to shrubs more than 12 feet tall.
Rhizomatous begonias are generally grown for their leaves, not their flowers. They range from tiny miniatures to the variety "Freddie" with leaves that will grow more that 3 feet in diameter under ideal conditions. The plants grow from rhizomes that creep along the ground, so they can be very large plants but do not grow very tall. The best known rhizomatous begonia is the Rex begonia. They have large leaves in various shades of red, purple, white and green.
Tuberous begonias are also commonly grown as bedding plants. They can have flowers as small as 1/2 inch across or spectacular ruffled flowers the size of a dinner plate. "Picotee" is a popular variety because of its light petals with dark edges. The plants can grow to be 3 feet tall in pots, slightly taller in the ground in ideal climates. Tuberous begonias go dormant in the short days of fall and start growing again in the spring. They can be upright plants, spreading plants or hanging basket plants. Tuberous begonias grow best where humidity is high but must have well-drained soil. The tuber will rot if they are over-watered.
There are a few begonias that do not fit into any of the standard classifications. Two of these are trailing-scandent and thick-stemmed begonias, the largest types of begonias. The first of this type to be discovered was Begonia glabra. Trailing-scandent begonias grow along the ground or vine up tree trunks. They can grow from 6 inches to 8 feet or more. They form roots at the nodes and can spread over large areas. Thick-stemmed begonias develop treelike stems and in warm climates can grow 20 feet tall.
- American Begonia Society: Virtual Greenhouse
- American Begonia Society: Cane Begonias
- American Begonia Society: Shrub Begonias
- American Begonia Society: Rhizomatous Begonias
- The National Begonia Society: Rex Cultorum
- American Begonia Society: Tuberous Begonias
- Hortus Third: Staff of the L.H Bailey Hortorium
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