Each year the National Garden Bureau declares a “year of” that features four plants: one vegetable, one perennial, one annual, and for the first time in 2016, one bulb. We looked at the Year of the Carrot earlier in the month. Now let’s look at this year’s annual, the begonia. In coming weeks, I’ll look into the other two winners.
With more than 1,700 species, Begonia is the fifth largest genus of flowering plants in the world, with almost an almost pantropical distribution: South and Central America, Africa, and Southeast Asia. The genus was named by the French botanist Charles Plumier for his friend, Michel Bégon, governor of the island of Saint Domingue (now Haiti) and a serious amateur botanist.
What is a Begonia?
The genus is composed of a wide range of mainy herbaceous plants (a few are semi-woody), including some with rhizomes and tubers, most adapted to moist tropical or subtropical climates. Nearly 15,000 hybrids of these popular plants exist. Although a very few species show some adaptation to temperate climates (B. grandis, for example, is hardy to zone 6b), most are grown as houseplants or as bedding plants, treated, in the latter case, as annuals in cold climates. They are also grown as perennials in hardiness zone 10 and above. Some begonias are grown mainly for their beautiful, often exotically colored foliage, others for their attractive, abundant and long-lasting flowers.
Most gardeners with a bit of experience can recognize a begonia on sight, but here are few pointers for beginners:
The leaves are alternate and usually asymmetrical (they are often ear-shaped or wing-shaped);
- There are usually distinct nodes (bumps) on the stem;
- The flowers are quite distinctive, with two opposite sepals much larger than the pair of much smaller petals, borne at right angles to the sepals. This is however really only obvious with single flowers.
Female flowers have a winged ovary behind their tepals. It usually has three wings.
Begonia flowers are monoecious (male and female flowers appear separately but on the same plant). Its winged ovary readily distinguishes the female flower from the male flower. If the female flower is fertilized, the ovary becomes a capsule filled with numerous very fine seeds that, in nature, are carried far and wide by the wind, ensuring the species’ survival. Many species are epiphytes and grow on tree branches or trunks.
Horticulturists like to put plants into categories, but begonias have always given both taxonomists and gardeners a hard time. After all, how can you bring order to chaos? Some botanists accept no less than 87 sections in the genus, while some horticultural classifications include dozens of groups. However, begonias, even from different continents and with different numbers of chromosomes, will often readily cross, so many plants have traits belonging to two different classes and sections and thus fall through the cracks.
Here is a simplified classification that might be useful for the ordinary gardener, although it is certainly too simple for serious begonia collectors.
A. Fibrous-rooted Begonias
This category is a bit of a misnomer: all begonias have fibrous roots. However, it is commonly used to describe all begonias that have only fibrous roots, therefore neither rhizomes nor tubers. Fibrous-rooted begonias can be short to tall and may be grown for their foliage or their flowers.
A1. Wax Begonias (B. x semperflorens-cultorum)
Traditionally, this group includes only one hybrid species: B. x semperflorens-cultorum, the popular wax or bedding begonia. This is a relatively compact plant with erect stems and glossy, somewhat spoon-shaped leaves, green or bronze in color. The flowers are small but numerous, in various shades of pink, red and white.
For convenience sake, I like to include two more recent introductions in this category: so-called B. x benariensis (I’m far from sure the name is botanically valid) such as the ‘Big’ series (plants twice as large as the usual B. x semperflorens-cultorum, but otherwise very similar) and Dragon Wing and Baby Wing series, with arching stems and wing-shaped leaves.
These begonias are usually produced by seeds and treated as annuals, but you can also multiply them by division or stem cuttings. You can also prolong their life by moving them indoors in the fall to serve as houseplants.
A2. Other Fibrous-rooted Begonias
Typically begonia authorities divide this group into many subcategories, such cane-like begonias, shrub-like begonias, thick-stemmed begonias and trailing or scandent begonias. However so few are available through in the average garden center that I find this creates confusion rather than simplifying things, so I prefer to lump them all together into a single category.
Often these begonias have erect stems, although often arching at the tip, stems with very obvious knots and highly asymmetric, wing-shaped leaves (they are often simply called “angelwing begonias” for that reason), although there are many exceptions: plants with climbing or pendant stems or with leaves that are star-shaped or even compound. Their foliage is often the main attraction: it often shiny, hairy, purple, red, or dotted with silver. The flowers tend to be small and usually pink, red or white, rarely orange. Some species branch abundantly, others tend to produce few ramifications, even when you pinch them.
Usually these begonias are grown as houseplants in temperate climates, although they also do wonderfully planted outdoors for the summer. In the Tropics, they are treated as perennials or small shrubs.
Fibrous-rooted begonias are usually multiplied by stem cuttings or by division.
B. Rhizomatous Begonias
These begonias have a rhizome: a usually creeping stem (although some rhizomes are upright) that root in contact with the soil as they grow. The plants tend to get wider as they age, but to remain low growing. This category is traditionally divided into 2 parts: rhizamotous begonias per se (a sort of holdall category) and rex begonias.
B1. Rhizomatous Begonias
This is the largest category of begonias, with hundreds of species and thousands of cultivars. Most are fairly compact plants (but there are also varieties with very large leaves), often with round or star-shaped foliage. The flowers are usually pink or white and tend to bloom during the winter, since most require short days in order to bloom. Most are mainly grown for their attractive and often very colorful foliage.
Until recently these begonias were generally considered houseplants, but gardeners have begun to discover they also make excellent annuals for shady flowerbeds.
This group is usually multiplied by stem cuttings, leaf cuttings or division.
B2. Rex Begonias
This subcategory of rhizomatous begonia includes hybrids derived from the long-lost species B. rex crossed with other begonias. The resulting hybrid species is called B. x rex-cultorum. The foliage of rex begonias is particularly colorful, coming in all imaginable shades of green, red, silver, purple, brown and pink, often with metallic highlights. Originally rex begonias had leaves that were more or less ear-shaped, but there are now varieties with star-shaped and even spiral leaves. Although most have creeping rhizomes, some do have upright ones. These begonias are normally grown uniquely for their foliage and little attention is paid to their rather sparse white or pink flowers.
Rex begonias are propagated in the same ways as other rhizomatous begonias and require much the same care. They are however considered harder to grow well, especially over time. Many varieties go into a sort of semi-dormancy in the winter, losing many or most of their leaves. If so, temporarily reduce their watering, letting the soil dry out more than usual, while still maintaining good atmospheric humidity. Start watering more abundantly when the plant shows signs of new growth.
Long considered houseplants, rex begonias have begun to star in shadier parts of the summer garden in recent years.
C. Tuberous begonias
These begonias have a tuber, an underground organ much like a potato, and differ from most other begonias in that they go fully dormant for months, losing both leaves and stems.
C1. Hybrid Tuberous Begonias (B. x tuberhybrida)
This is the classic large-flowered tuberous begonia gardeners have salivated over for generations. Most have extremely double, extremely large flowers (up to dinner plate size!) and come in a variety of colors: pink, red, yellow, purple, white, orange, etc. Often the flowers are bi-colored or have fringed margins. The stems may be upright or drooping, the latter often used in hanging baskets. There are dozens of classifications for these begonias (Picotee, Fimbriata, Pendula, Crispa, etc.), but you don’t need to know how to classify them in order to grow them!
The very popular ‘NonStop’ series, used extensively in flowerbeds worldwide, belongs to the Multiflora division, famous for flowers that are somewhat smaller that most other tuberous begonias (although much larger than those of other types of begonia), but as the name suggest, are produced profusely through the entire summer.
This begonia goes fully dormant in the fall and starts to grow again in the spring. Traditionally the tuber is dug up after the leaves are killed by frost, then kept dry and fairly cool during the winter. They can be stored in vermiculite, peat, sawdust, or newspaper or, if you grow them in pots, just pile the pots one on top of the other in a dark corner. The tubers start to sprout all on their own towards the end of the winter. Repot and start watering them in March or April, about 1-2 months before its time to plant them out.
Multiplication: seed and stem cuttings. You can try dividing larger tubers, but the cut surface often fails to heal properly, which can lead to rot.
C2. Bolivian Begonia (B. boliviensis and its hybrids)
Everything old is new again. My father used to grow this begonia when I was a young child, then it seemed to disappear from the market for decades. It suddenly came into prominence again around 2007 when the cultivar ‘Bonfire’, with orange-red flowers, very much like the old plants I remembered, was introduced. There are now many other varieties in shades of red, orange, yellow, pink and white. The leaves are long and narrow and the flowers have long pointed tepals, giving a tubular flower that hummingbirds love. This cliff-dwelling species has a naturally trailing habit, but there are now more upright cultivars and ones with more open, less tubular flowers.
This begonia goes fully dormant in the fall. Its tuber can be huge! Maintenance and multiplication is exactly like hybrid tuberous begonias and it fact, it is one of the parent species of this group.
C3. Hiemalis Begonia (B. x hiemalis)
This hybrid species often goes under the names Rieger begonia or Elatior begonia after two hybrid series that were once very popular. Hiemalis means “of winter” and these plants are naturally winter blooming. They come from a cross between summer-flowering tuberous begonias and the rarely grown winter-flowering species, B. socotrana. Despite their theoretical winter bloom, nurseries now offer hiemalis begonias all year long, even as bedding plants for the summer garden. This is done by offering the plants artificially short days. Indeed, once flowering is initiated under short days, the plant will continue to flower for 3 to 4 months even under long days, a technique that makes this plant a very good choice for the summer garden.
The flowers are smaller than those of most tuberous begonias, although larger than other begonia types. They are usually double and come in almost every color except blue. Modern hybrids bloom so profusely that you can scarcely see the foliage! After flowering, the stems start to die back. Ideally, you should cut the plant back at this point and let it rest for 5 or 6 weeks before starting another growing cycle… but hiemalis begonias are notoriously difficult to recuperate at the end of their season, so most gardeners simply buy new plants every year.
Propagation is by stem cuttings… but you may struggle trying to keep the cuttings alive.
C4. Lorraine or Christmas Begonia (B. x cheimantha)
This begonia results from a cross between the winter-flowering B. socotrana and the semi-tuberous B. dregei. The first cultivar was named ‘Gloire de Lorraine’, hence the common name Lorraine begonia. And it is also called Christmas begonia because of its early winter blooming period. Its abundant simple flowers are usually pink or white. Propagation is by stem cuttings… but as with the hiemalis begonia, it is not easy to maintain this plant from one year to the next. This begonia has largely been replaced in garden centers by the hiemalis begonia.
C5. Semi-tuberous Begonias
The most common species in this category is B. dregei, a species with a swollen stem base (caudex) and small white flowers, often used in bonsai. With its small leaves and decent branching habit (a bit of pinching will be needed), it looks like a small tree even if its stems are not truly woody. This begonia goes semi-dormant in winter: cut back on watering at that time. Propagation by stem cuttings and seeds.
General Begonia Culture
With such a wide range of different plants, you’d expect to need a lot of varied instructions on how to cultivate them all, but in fact, most begonias do best under pretty similar conditions… as long as you respect their growing season, because some, as mentioned, go dormant and don’t need light or watering for months on end.
In general, begonias prefer partial shade and many will tolerate full shade. Over time, however, many sun-tolerant tuberous and wax begonias have been developed and they do well in full sun, at least in northern regions. Give your begonias rich, loose, well-drained soil, moderate watering (only during the growing season, of course) and decent atmospheric humidity (indoors) and you should have no trouble growing them. They grow as easily in pots (indoors or out) as in the ground. Regular fertilization (during the growing season, of course) will stimulate better bloom, especially for plants grown in pots outdoors and therefore exposed to rain (rain, as wonderful as it may be for plants, has the annoying habit of leaching container soil of all its minerals). In the fall, except in hardiness zones 10-12, almost all begonias will need to move indoors if you want to save them from the cold.
The easiest and quickest method of multiplying begonias is by stem cuttings, a technique that works with almost all varieties. Simply slip a 3 or 4 inch (8-10 cm) section of stem into damp soil, keep the mix moist and the air humid for a few weeks and you’ll soon have a new plant.
Rhizome cuttings are just as easy, the only difference being that you press the rhizome horizontally into the growing mix rather than placing it upright.
You can multiply many begonias (especially rhizomatous begonias, including rex begonias) by leaf cuttings as well.
Take a healthy leaf and insert its petiole into a pot of moist growing mix. No rooting hormone is necessary, but high humidity helps. Thus, it is wise to cover the pot with a transparent plastic bag. Place the cutting in a moderately lit spot and at fairly warm temperatures (21˚C or more)… and wait. A small plant will sprout from the soil after a month or two.
If you need many plants, you can even use leaf sections as cuttings. To do so, cut a leaf into pieces, each with a small bit of midrib or primary vein, and press the sections into moist growing mix. Alternatively, press an entire leaf flat against the soil and cut its veins with a knife: a baby plant will soon poke out of each cut vein.
Begonias are notoriously difficult to grow from seed. The extremely fine seed gives seedlings that are tiny and very fragile at first, and their growth can be slow. It’s often more logical to buy trays of plants in the spring instead of trying to start them yourself. However, if you want to try growing begonias from seeds, here’s how:
You’ll need to so the seeds of begonias you want to plant out very early in the season, in January or February. At that season, however, days are still short, yet begonias need good light to germinate. As a result, germination can be poor or irregular and initial growth almost nil. That’s why it’s best to start begonias under lights, as that gives you full control of day length. Use a timer to set your lamp to 14 hour days: that will ensure good germination and equal growth. Especially don’t expose tuberous begonia seedlings to short days, as they are long day plants and therefore need days longer than 12 hours in order to bloom. In fact, if tuberous begonia seedlings are exposed to short days, that will stimulate tuber formation and put an end to their growth for the season, long before they have time to bloom..
Most begonia seeds sold today are pelleted seeds, making them easier to handle. On the other hand, pelleted seeds are also much more expensive.
To sow the seeds, fill a pot or seed tray with moist potting mix, level, and apply the seeds to the surface. Press them lightly into the mix without covering them with soil, because begonia seeds need light to germinate. Spray the container with warm water and put the seed container in a clear plastic bag or inside a mini-greenhouse.
Place the container in about 6 to 12 inches (15 to 30 cm) below a fluorescent lamp. Its gentle heat will help germination, as it should remain above 72˚F (21˚C) day and night. In 7-14 days, sometimes longer, you should see very tiny green leaves appear. At that point, remove the bag or dome to increase air circulation.
Transplant the seedlings in small individual pots when they have two or three leaves. Keep the soil slightly moist (you have to water very gently, preferably from below, as water pouring from the watering can’s spout can easily knock over or bury fragile young seedlings). Also, fertilize occasionally with a soluble fertilizer.
When outdoor temperatures remain above 50˚F (10˚C), acclimate the seedlings to garden conditions and transplant them, preferably into partial shade. Or continue to grow them indoors if you want to use them as houseplants.
Fun Facts About Begonias
- The tuberous begonia ‘Kimjongilia’ is one of North Korea’s floral emblems. It blooms annually on the birthday of the country’s late president, Kim Jong-il.
- Only male flowers of tuberous begonias have double flowers. Begonia experts remove the female flowers to give male flowers more energy to bloom.
- Begonia flowers are edible and in fact very rich in vitamin C. Their pleasant sweet/tart taste comes from the oxalic acid they contain, the same product that gives spinach and rhubarb their flavor. Since oxalic acid can be toxic if consumed in large quantities, it is best to consume begonia flowers in moderation.
- In the language of flowers, begonia means “beware”.
- Begonia seeds are among the smallest in the vegetable kingdom. One gram of begonia seeds can produce up to 100,000 seedlings!
- Every two years, in August, the Grand Place in Brussels is covered with a huge carpet of tuberous begonia flowers. It takes 120 volunteers about 4 hours and about 600,000 begonia flowers to compose the carpet. The show is spectacular, but don’t miss your flight, as it lasts only three and a half days!