Begonia collection at OpdeHaar

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Begonia grandis hardiness

Begonia grandis ssp. Evansiana is fairly widespread throughout China and Japan and its common name of “Hardy begonia” sums up the major claim for its inclusion in the hardy exotic hall of fame. It came through the winter of 2008/9 in our gardens without any special protection but I think I would cover it in dried leaves if temperatures dipped below – 10oC or so although we have never lost plants in the 20 years we’ve had them. 

As the photos illustrate, it is instantly recognisable as a begonia. Many gardeners may just walk past it thinking that it is a pot plant which has been pushed in for the summer to fill in a space. Nothing could be more wrong – stop and look more closely! If the planting can be arranged, try and position it so that the spectacular red undersides of the leaves are visible. A side view of the plant or looking up at it on a slope are two ways of achieving this.

It thrives in quite deep shade and although moisture is preferred it can cope with dry conditions and, once established, a fair level of sun, thus making it an excellent woodland plant. When the first frosts arrive, it dies off above ground but the tuber rootstock lives on and new growth emerges the following spring. Reports on the Internet hint that this emergence is “late”. In my experience, I find that it is the extent of exposure to sun which is a major factor here. In heavy shade, it can be towards the end of April before growth is seen but, even after a normal winter, there are signs of life in a sunnier position in early April. It could possibly be related to the extent to which the soil has been warmed.

Seedlings and bulbils

As growth gets underway, a crop of little seedlings will appear. These can be potted up and will grow away very easily. These are the result of bulbils which form in the leaf axils of the plant before the leaves die in the autumn. These bulbils are nascent tubers. They germinate very easily and provide a straightforward means of vegetatively bulking up all the different B.grandis cultivars.

By this time, you are probably wondering where “the catch” is in this story. I can honestly say that I haven’t managed to find it yet! This is a wonderful shade plant and it isn’t at all difficult either to propagate or grow. Furthermore it isn’t irritatingly invasive although it provides offspring enough (from bulbils) for bulking up a group. It is a mystery to me why one doesn’t see it in all the garden centres. Normal flower colour is pink but there is also a white or “Alba” form. For readers interested in gaining more botanical insights into Begonia grandis, the Pacific Bulb Society is a good reference source.

Sports of Begonia grandis

Over the years, plant hunters and the occurrence of sports in nurseries have given rise to a variety of interesting cultivars and an article by Dan Heims of Terra Nova Nurseries provides a comprehensive summary of the situation of what is available to the gardener.

Heim’s article, based on a talk given to the US Begonia Society, complements a somewhat earlier blog by John Boggan which provides additional insights and completes an instructive review of hardy begonia which bring the gardener up to speed on what is going on in this sector of the plant world. 

The Flora of China recognises 3 subspecies in Begonia grandis. The plant with rather sturdy stems and a solid abaxial leaf pigmentation of broadly oval leaves invariably found under the name “Evansiana” is Begonia grandis ssp. grandis. The other two variants (Begonia grandis ssp holostyla and Begonia grandis ssp sinensis)  both have longer and weaker/thinner stems. Begonia grandis ssp holostyla has triangular-ovate leaves and from a gardener’s perspective seems to have been created especially for the “Nanjiang Silver” variant. In Begonia grandis ssp sinensis the red pigmentation is generally concentrated along leaf veins and sometimes stems. The majority of the Chinese B.grandis introductions fall into this subspecies. It goes without saying that this is only an extremely superficial look at the taxonomy. However it alerts one to the nomenclature which is appearing in nursery catalogues and plant labels.

Begonia Grandis at OpdeHaar

Begonia grandis in a raised bed
Begonia grandis in a raised bed

We have been growing several cultivars of B.grandis for several years and generally purchased new variants when we came across them out of curiosity. Left to their own devices they bulk up largely thanks to bulbils. This vegetative propagation preserves the integrity of the variant. In contrast to seed propagation where there is a risk of cross-pollination when different cultivars are in close proximity to each other. This isn’t a problem in the garden. However, it can in theory introduce a bit of confusion in the nursery trade. Cross-pollination is maybe the explanation why, when looking around nursery beds, occasionally one or two plants seem to have numerous subtle differences from the surrounding stock. That said, from a gardening perspective, if the difference is an improvement, then it is worthwhile. 

Leaf variegation: Terra Nova Silver Series

As you would expect from a renowned nursery, one line of Terra Nova’s thinking was how to incorporate the hardiness gene into the decorative begonia varieties associated with pot plants or annual bedding displays and Begonia “Silver Splendor” ( PP 21946 ) is an early example of this line of thought. I bought a plant a few years ago here in The Netherlands. I am writing these lines on 1 July 2021 and clumps of Silver Splendor are only just pushing through. This is a couple of weeks later than normally the case because of a late cold spring period, but late emergence is a characteristic associated with B.taliensis which is the pollen parent of the Terra Nova hybrid. This is about a month later than I expect to see B.grandis or B.sinensis varieties awakening from winter dormancy.

A very decorative foliage plant which emerges late in Spring but persists until the autumn frosts. It can easily be combined with early spring flowering plants whose foliage is gone by the time the Begonia starts to appear.

Begonia “Sparkle and Shine”

Some leaf sports of B.grandis combine decorative upper leaf surfaces with an earlier appearance in late April. Begonia “Sparkle and Shine” is an example and this and was christened by Russell Gardens in the USA. They also carry other hardy begonia varieties –  see their website . Their description of “Sparkle and Shine” below says it all:

Begonia grandis ssp.evansiana `Sparkle and Shine’, white, 15″, September-October. House cross (happened on the farm without any help, just “bulbils mixing it up” if ya know what I mean?). The color of an Ox’s blood fills the backs of these wide HEART-shaped leaves and a PROMINENT SILVER-overlay adorns the fronts! They SPARKLE and SHINE in the dappled sunlight. Shade. They colonize by bulbils so FALL and SPRING clean-ups will not allow this to happen.”

In our experience, “Sparkle & Shine” spreads very effectively from bulbil distribution and at the end of 2020 I harvested and pricked out bulbils in seed trays. (It is noteworthy that a small percentage of the bulbils gave rise to plants lacking the leaf variegation of the others and this reversion raises the question as to the extent to which sports and natural hybrids occur within B.grandis.) The following photographs illustrate the patterns on the upper surfaces of the leaves; it is somewhat reminiscent of the popular house plant, Begonia maculata.

Begonia “Nanjiang Silver”

Another variant collected by Dave Demers in Sichuan and introduced by the botanist Riz Reyes in the USA as Begonia “Nanjiang Silver” displays a more extensive leaf variegation. There are reports that the variegation decreases as the season progresses. I am still bulking up my own stock from bulbils to comment on this. My tentative observation is that the contrast associated with the variegation possibly appears to fade somewhat.

Blister or Reflective pigmentation

Recent work in Taiwan has shown that the white/silver variegation comes about because of air entrapment in the upper surface of the leaves and is NOT a chemical pigment related phenomenon.  This is a device used by a variety of plants to prevent excessive exposure to sun from causing leaf burn by reflecting the sun like a mirror. Not surprisingly, it is referred to as Blister or Reflective pigmentation. If you take a leaf of “Nanjiang Silver” and look at it from different angles you will notice that the variegation seems to change; a similar phenomenon occurs when you walk around a plant. When you view a clump of “Sparkle & Shine” with their leaves blowing in the wind, the reflection of light really can induce the sparkle and shine – just like children playing with tiny mirrors to reflect the sun’s rays!

Begonia Nanjiang Silver showing old and new leaves
Begonia Nanjiang Silver showing old and new leaves

Inspection of Terra Nova’s “Silver Splendor” indicates that the silver colour here is also most likely a result of blister variegation. The fact that the extent of leaf colouration remains both constant and extends to well over 90% of the adaxial leaf surface is consistent with the Taiwan findings that the efficiency of photosynthesis is not impaired by air entrapment. This proposal then prompts one to ponder as to why the leaf patterns on the two variegated Begonia grandis cultivars do not seem to be constant and this could provide an interesting extension to the Taiwan findings. From my limited observations, the first leaves appearing on “Nanjiang Silver” almost rival those of “Silver Splendor” but the extent of this silver colouration diminishes – seemingly progressively – on new leaves . The photo illustrates this. By contrast, my early observations indicate that the level of leaf pattern retention (i.e. spots) is much higher on “Sparkle & Shine“.  Although I cannot claim the rigour of a scientific study, differences in light intensity do not appear to be key to these differences/changes.

Colour variation in Begonia’s

For completeness it is worth noting that there are two more mechanisms which give rise to colour variegation in Begonia leaves. The vivid colours so characteristic of Begonia rex houseplants and the deep red-purple on the underside or abaxial leaf surface of Begonia grandis are associated with anthocyanins. These are the same chemicals which are responsible for the vivid autumn colours in some deciduous forests. In the context of Begonia see brief details here.

Quite a few woodland plants found in shaded areas have a heavily anthocyanin pigmented abaxial leaf surface. It is often stated that this reflects light back through the leaf to give the chlorophyll a second chance to utilize it in photosynthesis. American botanists recently set out to test this hypothesis and found it not to be the case. Although their conclusion amounted to not knowing what the function of the pigmentation is, their paper provides a nice summary of the various proposals of what the role of anthocyanin might be.

The red/purple anthocyanin pigmentation occurs in random areas on the under surface of Begonia taliensis leaves where it generally escapes notice. However, it is this abaxial pigmentation which causes the dark leaf motteling when plants are viewed from above. As is the case with B.grandis variants, it is quite possible that the degree and extent of anthocyanin pigmentation will vary in different populations of B.taliensis and it would be interesting to see if selective propagation could maximise/enhance this decorative feature. 

Some Begonia, notably B.pavonina, develop a blue iridescence in low-light conditions and recent studies indicate that this arises thanks to the formation of highly uniform structures within the leaves which scatter light in a very regular manner. This finding at Bristol University has been further elaborated by Chinese botanists.

Chinese Begonias & hybrids 

It won’t come as a big surprise to learn that Chinese botanists have identified and are growing numerous Begonia species. Many of these will or are likely to display (a degree of) winter hardiness. A publication entitled “Diversity and conservation of Chinese wild begonias” provides interesting insights into the wide variety of Begonia species. Of particular interest, are the comments from these expert Chinese botanists on the “Morphological diversity”. (See section 1.3 of the paper on Chinese begonia). They highlight the diversity of leaf type, colour and variegation and the paper contains excellent illustrative colour photographs. However, their comments on natural hybrids provide food for thought bearing in mind the variations we have referred to in Begonia grandis and the sorts of deliberate crosses conducted by Terra Nova Nurseries.

In summary, they point out that different species in the same locality do form hybrids and site B.helmslyana, B.longifolia and B.palmata as doing this particularly frequently. However, most of these hybrids are F1 in character and so their continued existence depends on the proximity of the parent plants being preserved. In short, the hybrids are sterile and do not self-propagate; much like Begonia “Silver Splendor”.  Dan Heims reports that although numerous interesting hybrids with B.grandis had been produced, at the time of his report, they lacked the hardiness gene.

Begonia taliensis, Begonia petadifida 

The emphasis of this short review is on B.grandis and its cultivars but other candidates for use or for trialling in the garden are starting to appear in specialist nurseries. I am growing B.taliensis and B.petadifida quite happily in the Central Netherlands. In the UK, specialist nurseries such as Pan-Global plants and Crug Farm list numerous Begonia species with various degrees of cold hardiness.  

Begonia Torsa

The one BIG exception to B.grandis hybrids lacking cold-hardiness comes in the form of a cross with a species reportedly from Bhutan and unidentified but which contributes large leaves producing what to all intents and purposes is a B.grandis on steroids once tubers are mature. This rejoices in the name Begonia “Torsa”. A short article by Paul Tsamtsis of the Sacramento Branch of the American Begonia Society in 2001 describes it and also offers an insight into other B.grandis hybrids. He reports that New World begonia hybrids with B.grandis are weak and that crosses with B.rexes lack hardiness. Maybe this is an appropriate time to emphasize that the various cultivars of B.grandis are stable sports or mutations rather than hybrids in the sense of species cross-fertilizing.

Begonia “Torsa” is interesting because, like its B.grandis parent, it forms bulbils and is an undoubtedly vigorous hybrid. It is claimed to exhibit a degree of winter hardiness. Indeed it comes through Dutch winters when protected by a layer of mulch. However, in a personal communication, Dan Heims told me that it wasn’t hardy in his region (Ontario, Oregon) where B.grandis itself is hardy.

I have only just acquired my first “Torsa” plants and can confidently state that B. “Torsa” looks every bit like B.grandis on steroids but lacks the intense red pigmentation on the underside of the leaf; leaf veins are red. One cannot help but wonder if back-crossing “Torsa” with either of the variegated B.grandis variants “Sparkle & Shine” or “Nanjiang Silver” would yield interesting progeny in terms of leaf variegation (upper and/or lower) and even enhanced winter hardiness and, if it isn’t asking too much, a start into growth in Spring rather than June/July. Maybe this would make a nice project for a botany student?

Begonia hybridization

For readers who are interested into looking in more detail at begonia hybridization, a publication entitled “Occurrence and characteristics of natural hybridization in Begonia in China” by Daike Tian and coworkers is interesting in that it tabulates the hybrids they have identified and lists out the parent species of the hybrids and other useful data.

It is noteworthy that B.grandis does not occur at all frequently as a parent species in the hybrids. This and other work start to create a feeling that maybe Begonia somehow have a facility to genetically adapt to a location provided there is consistency in the environment. I’m maybe totally wrong on this but it is a point for discussion.  

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