Begonia x tuberhybrida
Bulbs and bulblike plants, Perennials, Shrubs
Grown for textured, multicolored foliage, saucer-size flowers, or lacy clusters of smaller blooms.
Grow as perennials in Zones 14-24, H1, and H2, except as noted. Can also be grown as annuals anywhere or dug and stored. Outdoors, most grow best in pots in the ground or in hanging baskets in filtered shade, with rich, porous, fast-draining soil, consistent but light feeding, and enough water to keep soil moist but not soggy. Most thrive as indoor plants, in greenhouse, or under lath. Some prefer terrarium conditions. Almost all require at least moderate humidity. In areas with hot, dry summers or indoors in winter, set pots in pebble-lined saucers or trays kept filled with water to below pot level.
Most are easily propagated from leaf, stem, or rhizome cuttings. They also grow from dust fine seed. Of the many hundreds of species and varieties, relatively few are sold widely.
Begonia x tuberhybrida
Best in Zones 4–6, 15–17, 21–24, and H1; possible in 7–9, 14, 18–28, 31, 32–with attention to humidity. Annuals in all but hot, dry climates. Among the best-known begonias are these magnificent large-flowered hybrids that grow from tubers. Members of this group range from plants with saucer-size flowers and a few upright stems to multistemmed hanging basket sorts covered in blossoms. With the exception of some rare kinds, they are summer and fall blooming.
Strains are sold as hanging or upright. The former bloom more profusely; the latter have larger flowers. Colors include almost everything but blue; shapes are frilly (carnation), formal double (camellia), and tight-centered (rose). Some have petal edges in contrasting colors (picotee). Popular strains include Double Trumpet (improved rose form), Prima Donna (improved camellia), and Hanging Sensation. Begonia boliviensis, cascading begonia, is a particularly lovely hanging type with profuse orange-red blooms.
Most gardeners grow tuberous begonias in containers. Buy dormant tubers (the bigger the better) in midwinter. Set them in pots filled with a rich, humusy soil mix, placing them indented side up and covering them with no more than 1/4 in. of mix. If you're planting a number of tubers, it's easiest to start them in a flat or shallow box, spacing them about 4 in. apart. Place pots or flats in a well-lit spot (but not in direct sun) where temperatures will remain above 65°F/ 18°C; keep soil moist but not saturated during the rooting period. When the tubers have produced two leaves, move them outside, weather permitting (night temperature must remain above 50°F/ 10°C); or pot up plants started in flats.
You can also plant begonias in the ground at this point; amend the existing soil, using 1 part soil to 2 parts potting mix. Choose a spot in filtered shade, such as under lath; or plant in an open area with eastern exposure. Water enough to keep soil moist but not soggy. For best bloom, mist with water several times a day unless you live in a cool or foggy area. Watch for fuzzy white spots on leaves; these signal powdery mildew. Begin feeding with liquid fertilizer a week or two after plants reach the two-leaf stage. For largest possible blooms, you can use a half-strength solution every other week, but monthly regular-strength feedings yield fine plants.
When leaves begin to yellow and wilt in fall, gradually reduce watering and stop fertilizing. When leaves fall off, lift tubers, shake off soil, and dry in a cool, dry spot for several days. Then store in a cool, dry place such as a shed or garage until spring; when small pink buds appear, plant the tubers once again. (You can also buy small seedling plants each year in early spring and plant them out in pots or in the ground.)
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