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Tuberous Begonias

Tuberous Begonias are probably the most commonly grown begonias worldwide.

The tuberhybrida types are always popular and are commercially grown in many countries. Unlike the other types of begonias, tuberous begonias grow from a bulb like structure and most go dormant part of the year. These die back completely, leaving only the tuber, which requires special storage.

Display at Christchurch Arboretum NZ, photo by Mike Flaherty.
Display at Christchurch Arboretum NZ, photo by Mike Flaherty.
There are a few begonias placed in the tuberous class, which don’t have tubers but form a caudex. There is some debate as to whether these should be in this class but currently they are commonly called semi-tuberous. More correctly they should be called caudex forming begonias.

Tuberous begonias were one of the first types of begonias to be hybridized. Combining aspects of the various species, hybridizers have developed types with large double flowers. This type is called tuberhybrida.

There are also a few dozen well known species with various unique qualities. There are just as many other species that have been newly discovered or are not in wide circulation.

There are also various hybrids between tuberous and other types such as Riegers, which don’t have tubers but have some tuberous qualities.

For purposes of this article, the tuberous types are divided into five main types, tuberhybrida, species, caudex forming, hiemalis and cheimantha.

Tuberhybrida Type Tuberous

This is by the far the most widely grown type of tuberous begonias. This is also probably the most popular type of begonia worldwide. Over many decades of hybridizing work, various species traits were combined to create what we know as the tuberhybrida type today. Much work continues today in Europe, Australia, New Zealand and North America to come up with even more improved varieties.

The most attractive characteristics of the tuberhybrida are their double flowers. The flowers come in every color but blues. There are also various styles of flowers from ruffled petals to rose forms. There are even picotee type tuberhybrida that have petals with edgings of different colors. Most are upright growing but there are also hanging types with trailing stems called pendula tuberhybrida. The flowers range in size from a couple inches as in the commercial Nonstop(TM) varieties to named varieties that can have dinner plate sized blooms with proper culture. There are also scented varieties available. Not all tuberhybrida have double flowers, there are many with single and semi-double flowers but these are less well known or new introductions. An example of this is the Mission Bells series which resulted from crossing tuberhybrida back to tuberous species to gain new traits.

All tuberhybrida go dormant for the winter. All upright varieties usually require staking to support the flowers. Unstaked plants can break off at the tuber easily. I learned this the hard way. I had a garden party and a friend was admiring a perfect specimen that was a foot tall with a beautiful six inch picotee flower. My friend said “You really should stake that, a breeze could break it off”. 15 minutes later a gentle breeze broke it right off at the soil line. I’ve staked mine ever since. There are probably more books available on this type of begonia than any other type. Since this is a specialized type of begonia, further reading is recommended. An especially great book on tuberous is Begonias by Mike Stevens, available from many sources, including ABS and Amazon.

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Species Tuberous (and first generation hybrids)

Begonia 'Rudy Tuttie' photo by and hybrid by Mike Flaherty.
Begonia ‘Rudy Tuttie’ photo and hybrid by Mike Flaherty.
There are a few dozen types of species tuberous begonias. There are also as many first generation hybrids between the various species.

Many require specialized care or are unique so may require more research into the care for specific species. All grow from a tuber or similar root structure.

They come in a wide range of sizes, flower colors and sizes, and leaves. Several species types form bulbils in the leaf axils that can be collected and grown into new plants the next year. At least one variety, B. grandis variety evansiana, is winter hardy even in cold climates.
 

Most require similar care to the tuberhybrida but may be more tender or difficult to grow. Examples of this type are B. sutherlandii and B. boliviensis.

For a list of tuberous begonia species follow click here to see Brad Thompson’s Tuberous Species List. Examples of first generation hybrids are B. ‘Airy Fairy’, B. ‘Bumble Bee’ and B. ‘Santa Barbara’.

Caudex Forming Tuberous

B. suffruiticosa
B. suffruiticosa
This type is commonly called semi-tuberous but caudex forming or caudiciform is more proper. Nearly all are variations or hybrids of B. dregei. There are a couple that aren’t but all need similar care.

The caudex is a unique root structure that looks like a large tuber (which is how they got lumped in this group). It is usually half out of the soil. From this caudex small stems arise.

During stressful times or bad weather this type can lose all their foliage down to the caudex. Unless the caudex is rotted by over watering, new stems will come back from the caudex when conditions improve. This type does best in clay pots to avoiding keeping them too wet.

The caudex forming are commonly grown as a natural bonsai and do well in the shallow bonsai pots. This type is very mildew prone, especially during cool wet times of the year, but also nearly any time of year. They may require routine spraying with a fungicide to be successful with them.

Examples of this type are B. dregei var partita and B. dregei var glasgow. All have small leaves and most have white flowers like B. suffruiticosa pictured to the left.

Cheimantha Type Tuberous

This type of tuberous is not commonly grown, at least in the US. They are hybrids between B. socotrana and B. dregei or other types. They are winter blooming.

Credits / references:
Brad Thompson | Brad’s Begonia World