Calycanthus chinensis & hybrids at OpdeHaar garden

Sinocalycanthus chinensis
Calycanthus chinensis

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Chinese calycanthus is still considerably less well known than it’s North American counterparts and is reportedly not very widespread in China where it was discovered in 1963 by W.C. Cheng and S.Y.Chang who caused the confusion in the nomenclature by introducing it first as Calycanthus and then re-assigning it to a new genus, Sinocalycanthus. Both the above names occur in the garden trade and even permutations such as Sinocalycanthus chinensis. Its early horticultural history has been summarised by Gerald Straley. To complete this rather scientific introduction, the shrub is also described in The Flora of China

Natural habitat and cultivation

In the wild it occurs on wooded hillsides in Zhejiang Province in China. It is a deciduous shrub which grows fairly rapidly to between 2 and 3m high and somewhat less across. It has a loose, open habit and its cultivation requirements have been described as similar to those for Acers. I have always grown it successfully in full sun since I first came across a small shrub in Esveld’s Nursery (Boskoop, Netherlands) around 1998. I say this simply to illustrate its flexibility because when I purchased it, nobody could tell me much about it beyond a short report in Hillier’s Manual of Trees and Shrubs. It is completely winter-hard here in The Netherlands and is fairly robust in the sense that I moved it to our Fire and Ice garden in 2005 when it was quite full grown and it settled down without any sign of disturbance.

Flowers of Calycanthus

Its decorative value really lies in it’s large (8-9 cm diameter) porcelain-white flowers shown in the photographs – comparisons have been made with camellia blooms and it is indeed tempting to add that it shares cultivation requirements with these shrubs as well.

 

Sinocalycanthus chinensisSinocalycanthus chinensis
Calycanthis chinensis

The flowers appear in late spring to early summer (these photos were taken in June 2005 and June 2006) with a more sporadic flowering in the late summer (August-September) on new wood. A drawback of the flowers is that they can develop quite a severe black stain at the bud stage – this, I think, occurs when the bud is damaged in some way by insects or a cultivation “accident” rather than anything more inherent in the plant itself but I would appreciate any comments from people who have given closer attention to this phenomenon. I notice that Dan Hinkley expresses a similar opinion in his latest bible (“The Explorer’s Garden – Shrubs & Vines”, Timber Press, 2009, ISBN 978-0-88192-918-8). The flowers are unscented. I know this, but visitors and I just can’t resist the urge to check this out when flowers are there.

Propagation

Propagation is certainly very easy from seed and I see that this is obtainable over the internet – just search using the terms  “calycanthus chinensis” seed  and take your pick from the suppliers along with all sorts of undoubted practical advice on germination. I have taken seed pods off the tree in early winter and sown them in moist compost in a tray which I put under the greenhouse staging for the winter. Almost 100% germination occurred and in view of the fact that no other calycanthus shrubs are in the area, I am fairly confident I won’t have hybrids – more on this possibility later!  In this light, some purists may indeed choose to take cuttings. There are numerous references to “rooted cuttings” in the literature and nothing to imply that these present a problem but I haven’t personally explored.

Where to put Calycanthus in the garden

On the subject of placing the Chinese calycanthus in the garden, it isn’t a shrub, in my opinion, to grow as a specimen but more something in the background of a bed or, as in its natural habitat, as part of a woodland garden. I’ll be doing this with my seedlings – any potentially shade-tolerant shrub gets a trial here! It’s rather open habit renders it a candidate support for a large-flowered clematis to extend the period in which it carries flowers – something like Clematis florida “Sieboldii” would fit the bill nicely. Large, white flowers with a vivid purple centre from about July onwards would take over from the calycanthus blooms with a comparable effect. You could get a total contrast if you are skilful enough to persuade Tropaeolum speciosum to get going through the shrub but these effects are dictated by your personal taste.

Hybrids

The North American calycanthus varieties can form inter-species hybrids and it was the late J.C. Raulston who was the instigator of a trial to see if this extended to the Chinese species in the early ’90’s. A report from the Arboretum newsletter gives a beautiful sense of how things developed.  Read the report here.

Before we get bogged down in the nomenclature again, the accepted name of this new hybrid is Calycanthus x raulstonii “Hartlage Wine” and cuttings were released to horticulturists in 2000. I first learned about it when I was searching on the Internet a year or two after this and similarly subsequently read that small plants were available from Bulk’s Nursery in Boskoop (Netherlands) and promptly bought one (2008) and planted it out in the spring of 2009 at about 70cm tall. My plant is making a lot of sidegrowth as opposed to vertical growth to date and I have heard comments which indicate that this is a characteristic but that it adopts a vertical habit subsequently. We will see! However, another characteristic, which I can vouch for, is that it commences flowering at a very early age – mine was already flowering by the summer of 2009 as the photo shows. I have to confess that I didn’t check the blooms for the light scent which the American parent is said to confer on its offspring. I was, however, just a touch disappointed by the form of the flower which I felt lacked just too much of that of the Chinese side of the hybrid. Maybe the flowers on a more adult plant will put this latter feeling to rest. The JC Raulston Arboretum group have some really good comparative flower pictures that are worthy of study:  Click here for the link   

Calycanthus x Raulstonii “Hartlage Wine” Foto’s mei 2008

Inter-species hybridization

Hartlage Wine”  introduced the idea of inter-species hybridization and, as in so many endeavours, it is this rather than the actual execution of the idea that is the stroke of genius and it isn’t too surprising to learn that new hybridizations are being looked at. Probably the first of these with horticultural potential is Calycanthus “Venus”  from the team which took over J.C. Raulston’s baton at Raleigh.
This is now fairly readily available from good nurseries and illustrations and comments in the literature indicate that the flowers are highly reminiscent of a white magnolia and are scented. It would not be surprising to learn that other hybrids are being evaluated. Venus is available in The Netherlands and has recently been planted in our garden.   Three other new hybrids are Calycanthus floridus Athens, Calycanthus floridus Ferox and Calycanthus Michael Lindsay.

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