Begoniaceae – A Genus Worth Exploring

• By Pat Chadwick
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• January 2016-Vol.2 No.1
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• 4 Comments

I recall the day I became bewitched. It was a clear, sunny day some years ago at Longwood Gardens near Philadelphia. I was there at the invitation of a dear friend and fellow plant geek who lives nearby. As avid gardeners, we deeply appreciated our tour of Longwood and wandered through the gardens amiably discussing the merits of each plant we encountered. We were near the end of our tour when we came upon a strange plant that stood apart on a pedestal in the conservatory. Fascinated, we approached the plant tentatively, not sure what we were seeing. Its graceful, mounded shape draped demurely over the edge of the urn. The foliage shimmered ever so slightly in the light. Each leaf curled in on itself in sensual whorls of silvery green bands, alternating with deeper hues of forest green. Everything about this plant seemed exotic, yet oddly familiar. I was hooked.  I had to know more about this plant. We searched for the plant identification tag. It read Begoniaceae. I had been bewitched – by a begonia!

Begonias are generally regarded as common, ordinary, old-fashioned house plants. But that perception needs to change. There’s a vast world of begonias beyond the ones our grandmothers grew. My visit to Longwood Gardens that fateful day opened my eyes to the complex world of this large and diverse genus of plants. While many begonias bloom in glimmering shades of red, pink, white and more, in many cases the foliage is more interesting than the flowers. Any number of cultivars are available with leaves that are smooth, hairy, spotted, multi-hued, whorled, round, asymmetrical, and even star-shaped.  Of the more than 1,000 members of this genus (not counting the vast numbers of named and unnamed cultivars), the majority of them have one thing in common as shown in the photos below: asymmetrical leaf shapes.

Tiger Star Begonia

Iron Cross Begonia

Begonia – Unnamed Cultivar

DESCRIPTION

Begonias originally came from the tropical and subtropical moist climates of South and Central America, Africa, and southern Asia. The plants are monoecious. In other words, male and female flowers occur separately on the same plant. The male contains numerous stamens. The female has a large inferior ovary and two to four branched or twisted stigmas. These tropical perennials are generally treated as house plants. A few exceptions include wax-type begonias which are widely used as annual bedding plants in summer gardens, and a hardy variety, which can survive winters as cold as those experienced in Zone 6.

CLASSES OF BEGONIAS

Begonias are grouped within a complicated classification system that is based on flowers, method of propagation and foliage. Root structures are another important way to identify species and may be described as fibrous-rooted, rhizomatous, and tuberous.  The American Begonia Society divides the Begoniaceae genus into the following eight classes:

Cane-like: This is one of the more popular classes of begonia. Members of this class typically have fibrous root structures, an upright habit, and segmented stems that are similar in appearance to bamboo. The old-fashioned angel wing begonias fall into this class. Their name comes from the asymmetrical shape of their leaves, which are dark green with silver spots.   Dragon wing begonias are a modern-day hybridized version of the angel wing type. This more compact form has taken the gardening world by storm over the past few years. It has arching branches about 2 feet long, leaves that are shaped liked their angel wing relatives but without the silver spots, and masses of drop-dead gorgeous red, pink or white blossoms. This plant is suitable as a lone specimen or as a mass planting in a shady to partly shady spot.

Semperflorens: This second fibrous-rooted class includes annual or “wax” begonias, which are grown as bedding plants and sold by the millions in garden centers everywhere. Wax begonias get their name from the waxy appearance of their leaves. They grow quickly, look great when planted in masses or in container combinations, are deer resistant, and will thrive in either sun (except intense, hot afternoon sun) or shade. The cultivars with bronze-colored leaves work better in sunny locations whereas the cultivars with green leaves do better with afternoon shade.

Shrub-like: This third fibrous-rooted class grows upright on branching stems and can range in size from miniatures to giants up to 12 feet tall in more temperate climates. They get their name from their multi-stemmed habit. Rather than just a few stems, they produce a number of stems from the ground and branch freely, giving the appearance of a shrub. While this class of begonia has flowers, it is mainly grown for its foliage.

Rhizomatous: The rhizomatous family is the largest of the begonia classes and includes more than 700 species. They are distinguished by their thick stems or rhizomes which grow horizontally near the surface of the soil. New roots and leaves sprout from these stems. This class is valued for its interesting leaves, compact growth, and massive flower displays in spring.   B. erythrophylla, which is shown in the accompanying photograph, is an early hybrid called ‘Beef Steak’ because of its large round leaves. This plant’s striking foliage is dark, glossy green on top and burgundy on the bottom. When the light strikes the leaves, the combination of the two colors is sensational.

Rex cultorum: Just as its name suggests, this class is the “king” of the begonia world. Technically, Rex begonias are rhizomatous but they are classified separately because of their boldly colored foliage and more exacting growing requirements. In fact, they are often grown specifically because of their spectacular foliage. The brilliant colors, shapes, and forms are far more interesting than their blossoms, which tend to be pale and insignificant. Several hundred named Rex cultivars are available these days in addition to numerous unnamed hybrids, including some miniature versions with a mounding form.

Tuberous: This class is grown for its exquisite blossoms, which are huge and vaguely reminiscent of Camellia blossoms. In contrast to the other begonia classes, tuberous begonia foliage is fairly ordinary, but the blossoms are clearly some of the most beautiful of the entire species. The blossoms are frequently double or frilly looking and are available in a wide range of rich-looking saturated colors.  Some cultivars have picoted blossoms (edged in a color that contrasts with the primary color). Tuberous begonias go dormant in the winter. The fleshy, round tuberous root must be dug up in the fall and stored in a cool dry place over the winter. In spring, it may be replanted either in a pot or directly in the ground after all danger of frost has passed.

Begonia grandis, or hardy begonia, is another member of the tuberous class and hails from China. This form of begonia is unique in that it is hardy in gardening zones 6 – 9. This tough plant is slow to emerge in spring, but it quickly forms a ground cover as the summer heat arrives. It produces clusters of pink blossoms from midsummer to early autumn. The characteristic asymmetrical leaves are medium green with burgundy on the undersides. Hardy begonia is a good choice to plant in part or full shade as a mass planting, or as a companion to other shade-loving plants such as ferns or hosta. It’s also a good choice for planting under walnut trees, where not much else will thrive.

Trailing-Scandent: Compared to the other classes of begonia, this one is fairly small. The name is taken from its growth habit. “Trailing” means that the stems can extend downward toward the ground. “Scandent” means that the branches can be trained to climb, similar to a vine. For the gardener who loves hanging baskets of flowers, this begonia is for you. The trailing habit, glossy leaves, and showy display of white or pink flowers in the spring can be quite beautiful. The only down side to this class is that the pendulous stems are fragile and can be easily broken if you need to re-pot the plant. To help solve the problem, the stems should be pinched back to encourage branching.

Thick Stemmed: This is a class of begonia not commonly found commercially but should you encounter it, you’ll know it by its very thick stems with no discernible joints or nodes. This class of begonia sends up new growth from the base of the plant. As the stems lengthen, the lower leaves drop off leaving leaves on the tips of each stem and leaving the stems bare. The plant itself can grow quite large, reaching five to six feet in height. This is an unusual class of begonia that is difficult to grow and may best be enjoyed by the gardener who likes a challenge.

CARE AND MAINTENANCE

Begonias are generally quite easy to grow provided their cultural requirements for light, water, and humidity are met.

Light: If you’re growing begonias as house plants, locate them near a window with bright filtered (indirect) light. As a general rule of thumb, blooming types of begonias prefer more sun than the foliage types. Move them outside during the summer months, but protect them from the hot afternoon sun. They like morning sun but need afternoon shade.   Wax begonias that are used as bedding plants are better able to tolerate bright sun than other classes of begonia. The cultivars that have bronze-colored foliage are more sun-tolerant than the ones with green foliage. Tuberous begonias are happier with more shade, preferring less heat than some of the other varieties.

Soil: The important thing to remember is that the soil must drain well.  For bedding plants, work in some compost to improve the drainage. Use a light texture potting soil for containerized begonias.

Water: Both containerized begonias and those used in summer beds like to be kept evenly moist, but begonias absolutely do not like wet feet. Allow the soil to become almost dry between waterings. Overwatering can cause the plant to drop its leaves or cause root rot.

Fertilizer: Begonias benefit from a light feeding about once a month during the growing season. Use a balanced organic fertilizer and apply at quarter strength every two weeks or apply a controlled-release fertilizer every three months. Taper off on the fertilizer in fall and withhold it altogether during the winter months.

Temperature: Other than the one hardy variety (Begonia grandis), begonias do not tolerate cool temperatures. Move your containerized begonias indoors once night-time temperatures drop into the 50s F. Begonias prefer temperatures between 65° and 73° F.

Humidity: Most begonias thrive in a humid environment.   If the air isn’t humid enough, the edges of the leaves may become crisp. To increase humidity levels, place the potted plant on top of gravel in a pebble tray. Rex cultorum begonias are particularly finicky about humidity levels, requiring more humidity than the other classes of begonia. They appreciate being planted in a  porous planting mix and misted often with room temperature water.

Deadheading: Most begonias benefit from deadheading to keep the plants looking neat. Otherwise, the spent blossoms have a tendency to fall off and make a mess. Wax begonias (members of the Begonia semperflorens class), in particular, benefit from being deadheaded to help keep the floral show going.

Pinching: Most begonias do not need to be pruned back or pinched to make them fuller. Cane-like begonias are the exception. If allowed to grow unchecked, they can become leggy and sparse looking. To keep them looking lush and full, pinch the growing tip of each stem at the point where the next leaf will come out.

Potting: Plant begonias in pots that are just a little larger than the root ball. Begonias generally prefer to be a little pot-bound. If you grow the large cane-type begonia, pot them in a heavy pot that will not tip over when the plant grows top heavy. Transfer it into a larger pot when the plant needs to be watered very frequently.

Pests and Diseases: Begonias generally tend to be pest and disease free. They may occasionally be bothered by mealy bugs or aphids, and mildew may result from damp overnight conditions and poor air circulation.

PROPAGATION

Begonias are very easy to propagate. Ones with rhizomatous root structures may be propagated from stem or leaf cuttings.   I’ve even rooted a few in a glass of water. Begonias with fibrous roots may be divided. For more detailed information on propagation methods, see the link below for Virginia Cooperative Extension (VCE) Publication 426-002, “Propagation by Cuttings, Layering and Division.”

SUMMARY

Whether you are new to gardening or are a serious plant collector, you will enjoy growing begonias. Just don’t limit yourself to the commonly-grown types. Seek out some of the more exotic varieties. Most garden centers carry a broader range of begonias these days. A small, inexpensive plant can rapidly grow into a large, dramatic specimen in no time at all. The foliage and flowers are colorful and the diversity within this large family of plants is fascinating.  Check them out and don’t be surprised if you, too, become bewitched by begonias.

SOURCES

A-Z Encyclopedia of Garden Plants (American Horticulture Society, 2008)

“Propagation by Cuttings, Layering, and Division,” VCE 426-002. (https://pubs.ext.vt.edu/426/426-002/426-002_pdf.pdf).

American Begonia Society website (http://www.begonias.org) (Not to be confused with the National Begonia Society, which is located in the U.K.)

Longwood Gardens website (https://plantexplorer.longwoodgardens.org/ecmweb/FindPlant.html)