University of Vermont
Department of Plant and Soil Science

Spring News Article


Dr. Leonard Perry, Horticulture Professor
University of Vermont

Begonias are easy to grow, need only moderate care, and will reward you with a lovely display of blooms all summer long. Some are grown for just their colorful leaves, but most come in a range of flower colors.
Most begonias grow best in part shade (4 to 6 hours of direct morning sun a day), or filtered sun (as through trees).  Most will tolerate full shade (no direct or filtered sun), but won’t be as dense and usually have fewer flowers. A few grow in full sun.  They prefer moist, but not soggy, soils.  If powdery mildew disease plagues your garden, look for resistant varieties, don’t get water on leaves, and provide proper spacing for air circulation around plants. 
The begonia family is huge, with over 1,500 species and thousands of selections.  Such a large family may be divided into groups in several ways.  You may see them classified by root type—fibrous or tuberous (those with swollen yet flattened, brown tuber structures).  You may see them grouped by use—flowering or foliage.  Or you may see them grouped by habit-- shrub, spreading, thick-stemmed, or cane types.  While many are heirlooms that your grandmother may have grown, there are quite a few new and exciting introductions in recent years.
The tuberous are perhaps the most showy, with large single or double flowers in most colors.  Like other begonias, tuberous ones won’t tolerate much (if any) frost.  But, unlike others, once the tops die back in fall you can bring in the tubers and overwinter them indoors.  Store tubers either dry in their pots or, if dug from the garden, store them in dry peat moss.  Pot in early spring (March) or, if in pots already, begin watering lightly as growth resumes.
This tuberous group has some of the most exciting new introductions recently, mainly new cultivars (cultivated varieties) of the Bolivian begonia (B. boliviensis).  As its name indicates, the Bolivian begonias originally came from the eastern sides of the Andes mountains in Bolivia and Argentina.  Although the subject of new breeding and introductions, this species was first introduced to Europe in 1864 by Robert Pearce—a plant explorer for the famous Veitch firm of England.  This species was popular even then, such as when first exhibited in 1867 at the International Horticultural Show in Paris. There, it was said to have “attracted more of the attention, both of botanists and horticulturists, than any other plant then brought to that magnificent exhibition.”  This species is of horticultural significance, as it was one of the species used by John Seden in breeding the first hybrid tuberous begonia (B. x sedenii). 
The arching stems of the Bolivian begonia are clothed all summer in brilliant flowers, generally orange, pink or red.  Flowers are in pairs or threes, and have four pointed segments often flaring at the ends.  These fall off naturally when through bloom, so don’t need “deadheading”, and will be replaced continually with new flowers.
Leaves are pointed, of the angel-wing type.   They form clumps spreading to two feet wide, and about one foot high.  Although plants may overwinter in the warmest climates in the ground as tubers, in the north they’re best used as annuals in pots or hanging. 
Perhaps the most popular Bolivian begonia is ‘Bonfire’ with fiery orange flowers.  Similar are the Waterfall series, originally from Holland, with ‘Angel Soft Pink’, ‘Encanto’ in both orange and red, and three colors of ‘Victoria’.  The ‘Mistral’ series is available in red, dark red, and orange.  A popular cultivar released in 2014, ‘Upright Fire’ is part of the Unstoppable series.  ‘Lucky Strike’ is part of the Unbelieveable series, having lemon-yellow inner petals and peach-colored outer petals. Other popular Bolivian series you may find include Bon Bon, Beaucoup, Crackling Fire, Million Kisses, and Sparkler.  
Other crosses among tuberous species from the Andean mountains (B. x tuberhybrida) have lead to such series as the Go-Go begonias.  These come with various color flowers, on bushy plants.  Other upright ones include the Panorama series with smaller but more flowers, and the Ornament series with burgundy leaves and red or pink flowers. The Illumination series, in various colors, is a trailing or cascading group with double flowers.
“Nonstop begonias”, which were first developed in Germany, are perhaps the most popular upright series of tuberous hybrids, with double blooms in many colors. They are sensitive to daylength, the longer days of summer leading to faster and more flowers, and better plant quality.  Some of these tuberous hybrids, such as the Nonstop and Illumination begonias, can be started from seeds. This saves on cost, but plants take longer to reach flowering.
Of the flowering types, the most common may be the fibrous-rooted wax-leaf (often called semperflorens from the species name), and cane-type angel wing begonias.  The names are descriptive of their leaves, and their small flowers come in various colors of reds, pink, and white.  Wax-leaf are the ones you see used in masses in summer gardens, which can be potted before frost in fall and brought indoors. 
Fibrous or wax-leaf begonias, particularly those with bronze leaves, grow well in full sun in the north.  While there are many choices you’ll find in most garden outlets, the Whopper series (B. benariensis) has four times the size and impact of these traditional cultivars.
Angel wing begonias have winged-shaped leaves, often with white or silver markings.  These have been crossed with the wax-leaf types to create Dragon Wing begonias, available since the 1990’s.  They have the leaf shape of angel wing, but are green with no markings. 
A hybrid of the wax-leaf begonias and tuberous ones are the popular Reiger begonias.  Originally bred by Otto Rieger of Germany, and introduced to the U.S. in 1970, this group is more properly called Hiemalis begonias after its scientific name (B. x hiemalis), or Elatior as they’re known in Europe,  as there have been many developed since the original Riegers.
Elatior begonias have large single or double flowers resembling camellias, 2-inches wide, in various bright colors.   These begonias prefer soil on the dry side and don’t tolerate one that stays wet. They don’t grow well in hot, humid climates so are best outdoors in cooler northern climates.  They’re a common houseplant grown indoors in winter, so may be called “winter begonias”.
The Solenia series of Elatior begonias takes full sun, and leaves are mildew resistant.  They come in pinks, reds, and orange.  The Dragone series comes in colors of pastel pinks, orange, and white.
Of the foliage begonias, the most common are the Rex begonias (B. Rex-cultorum) with their large leaves,  in various shapes, and with striking colors and combinations including reds, silver, green, pink, purple, and gray.  All the variations you’ll find descend from one ancestor, the species (B. rex) native to the northeastern Indian state of Assam, which was crossed with other rhizomatous (those with underground stems) species to make our modern hybrids.
Rex begonias generally reach 12 to 18-inches tall, and leaves can get to 9-inches long and 5-inches, but generally are less. They make great houseplants, preferring warm conditions.  The Shadow King series is a recent one bred for shade outdoors.  ‘Gryphon’ is a popular new cultivar with deeply cut silvery leaves.
With most the traditional shade impatiens no longer grown, due to downy mildew disease, this provides a great opportunity to try some of these new and colorful begonias.

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