Seemingly infinite variety characterizes the genus Begonia. Plants can be long-stemmed or low-growing, have fuzzy or shiny leaves, and produce large flowers or ones so insignificant as to be almost invisible. Probably the most prized, though not the most widely grown, are tuberous begonias, whose name belies their fulsome displays of mid- to late-summer bloom. The flowers often resemble roses or carnations, and they rarely disappoint growers.
"In my garden I always have begonias," says Steven Frowine, respected consultant to the horticulture industry. "They come in strong primary colors and great pastels, and they bloom constantly, from summer until frost. I don't know of anything else with the same combination of flower size and shape that blooms in the shade."
Over the years, breeders have developed strains of tuberous begonias (B. tuberhybrida) that feature ruffled double flowers and "rose form" blooms, and some types have flowers that look like carnations or double camellias. Colors range from white through yellow, orange, apricot, pink, and red. Some have bicolor petals, such as white with a pink edge or yellow with a red edge. Begonias with petals that are edged in lighter or darker colors are called picotee.
Buy dormant tubers in winter, either by mail from a specialty nursery or from a nursery or garden center. Another possibility is to buy blooming plants in summer. (By the way, tuber size does not predict plant or flower size.)
Most gardeners buy dormant tubers, which are easier to grow than seed and less expensive than blooming plants. Tubers are also usually easier to find than blooming plants. Although it's possible to find tubers in nurseries in regions where they grow successfully, the best selection is from specialty dealers. Most of their plants have been grown from seed strains carefully bred for high-quality flowers.
Certain dealers also sell named varieties grown from stem cuttings, such as 'Avalanche', 'Bonfire' and 'Falstaff'. These are considerably more expensive because the supply is limited and cutting-grown tubers take longer to reach an appropriate size for sale.
Many gardeners shy away from tuberous begonias because of their reputation for being difficult to grow. They really aren't. Although travelers discovered the ancestors of these beauties in the Andes Mountains in the mid-nineteenth century, more than half of the United States has microclimates or growing conditions that can sustain tuberous begonias.
"It doesn't matter whether you're on a mountain or in a desert. Just remember the three conditions: day temperature, night temperature, and humidity," notes Skip Antonelli, second-generation proprietor of the begonia grower Antonelli Brothers. (As with most frost-tender bulbs, you can also grow tuberous begonias indoors in containers, or dig up the tubers in the fall and store them inside over the winter.)
Growing from seed rather than tubers is another option. You can grow thousands of begonias from one small packet of seed. Begonia seed is powder-fine, however, and requires sterile soil and careful control of temperature to grow. And plant size, quality, flower color, and form are also unpredictable. The plants take six to eight months from seed to bloom.
"I've grown tuberous begonias in many areas of the country--Hawaii, California, St. Louis, Philadelphia, Pittsburgh, and Ohio," says Frowine. St. Louis was the biggest challenge because of summer heat. If you shade them in the heat of the day and provide a place for them away from buildings that reflect heat on them, you can grow them in containers or in the ground."
Experts agree that this plant can tolerate daytime temperatures up to 90 degrees F. and, though warm nights are a pleasure for people, these begonias prefer evenings to be cool, around 55 to 60 degrees F. The third requirement, at least 69 percent humidity, is probably the easiest to meet.
Even if all three conditions don't occur naturally, a few growers' tricks can accommodate these demands. Where the temperature exceeds 95 degrees F., for example, an experienced grower will grow them in full shade under large shrubs such as camellias or rhododendrons, and mist all nearby foliage to lower the temperature and increase humidity.
Ben Herman of Tucson, Arizona, grows his plants in a greenhouse equipped with an evaporative cooler. "When I first tried tuberous begonias, they lasted maybe a week in my climate," he recalls. "That intrigued me. I'm always looking for a challenge!" Herman, professor of environmental physics at the University of Arizona, also compensates for his desert climate by ordering his tubers for delivery in late fall; he then sprouts them in November and enjoys four months of bloom, from late February to early June. This is the direct opposite of what most growers do.
Typically, in nondesert, temperate sections of the country, growers start tubers indoors as early as February and transplant them into pots or beds about two months later to bloom from mid-June until frost.
Even in San Francisco, where the cool, foggy summers are ideal for tuberous begonias, problems can arise. Longtime San Franciscans Alice and Isadore Gold have raised blue-ribbon tuberous begonias for several decades. "We have to give them a little attention because an extreme change from day temperature to night temperature can bring on powdery mildew," Isadore Gold acknowledges. But the Golds suggest spraying an appropriate fungicide to combat this common malady that disfigures begonias.
Several degrees' latitude to the north, the world-famous Butchart Gardens, on Vancouver Island in British Columbia, shares the Golds' experience of cold summer nights after warm days. The staff grows 16,000 plants a year from seed. Throughout the gardens, these begonias show their versatility, growing just the way they do in less-renowned gardens: in beds, various-sized containers, and hanging baskets.
Butchart Gardens mostly grows 'Non-stop' begonias in the beds because they tolerate heat and sun better. It uses the other, showier kinds in containers and baskets. ('Non-stop' begonias, which grow closer to the ground and have smaller flowers than most tuberous begonias, are descended from B. hiemalis.)
Steve Frowine grows tuberous begonias in containers rather than in beds because "You can create a habitat for them more easily," avoiding heavy soils and hot exposures.
In any climate (except the desert), winter storage of dormant tubers is important to their success year after year. Jack Babiash of Green Bay, Wisconsin, has grown 50 to 60 tuberous begonias annually for a decade. His tubers spend the winter on a table in his basement until mid-March. Eschewing some growers' practice of using artificial lights to start early growth, Babiash still enjoys three summer months of cheerful color following the plants' natural calendar.
February/March: Time to Plant
Once pink growth buds appear atop stored tubers, plant tubers concave side up and rounded side down in nursery flats or pots filled with moistened, well-drained leaf mold or coarse compost, then lightly cover the tuber with about 1/2" of the same mix. Place flats in a warm (70 degrees F.) room out of direct sun. Water to keep the soil moist but not soggy. Keep the plants indoors until all danger of frost has passed.
After the last frost in your area and when plants reach 2 inches tall, transplant each to its own pot or basket with the tuber lightly covered with about 1/2-inch of potting soil or, in the ground, with soil amended with at least one-third compost. Place them where they'll receive filtered sunlight, light shade, or morning sun followed by afternoon shade. Eastern and northern exposures are best. Fertilize every two weeks with a half-strength solution of fertilizer (approximately a 3-1-2 formula).
May through June: Showtime!
Tie upright plants to stakes. Watch for fuzzy white spots on leaves, signaling powdery mildew. If you see the white spots, spray foliage with a fungicide labeled for powdery mildew on begonias. Continue to fertilize (at half-strength) every two weeks or so, and water to keep soil moist but not soggy. No pinching or pruning is necessary.
September or first frost: Plants fade.
Bring outdoor plants into a well-ventilated, dry, and shady place. Withhold water, but don't remove faded stems until they drop off. Once the plant is gone, dig out dormant tubers and rub them gently to remove clinging soil; dry in the sun. Label the plants, noting flower color and whether upright or hanging-basket plants. Store dry tubers in egg cartons (or in a box but not touching each other) with their labels. Store them in a cool (40 to 55 degrees F.), dark place, and check them monthly to remove any soft, moldy tubers.
Chuck Anderson--the Santa Cruz, California "Garden Guy" and past president of the American Begonia Society--grows tuberous begonias in Rio del Mar. Laurel Taylor is also a tuberous begonia enthusiast based in Santa Cruz.
Photography by Netherlands Flower Bulb Center
Article published on June 23, 2008.