‘A’ is for Arboreum

by Norman Todd - January 2000


One of the difficulties in writing about rhododendrons is that the facts that allow one to make useful encompassing generalizations need about a century of observation.  One can be a writer on Canadian federal elections or US presidential elections and make some interesting, even predictive, comments by knowing what happened in the last ten or fifteen of them.  Writing about contemporary art requires only the study of a static object or two and a stack of metaphors.  Commenting on women’s fashions involves no risk at all because the creations being analyzed will never be worn by anyone reading the article.  Pontificating about life forms with a longevity greater than our own may be risked only because at the end of the day those reading this will not be around to criticize for significantly longer than the writer will.


These thoughts are prompted by a predilection to claim that one of the best species for a large garden in these parts is R. arboreum.  Also, I think arboreum is currently underused in hybridizing.  This hunch or bias is based on observation of a very small number of plants over a mere thirty years.


I have read about and even have slides of arbutus-sized arboreums in Nepal – sentinel columns of blazing red.   I am aware of a grand one in Dunbartonshire, Scotland which measures over forty by forty-five feet.  I am also aware of avenues of fifty footers in Ireland and of many other Methuselahs in Southern England which reputedly came from seed collected by Dr. Wallich, Superintendent of the Calcutta Botanic Garden.  He was not the first to collect seed of arboreum, this distinction going to a Dr. Buchanan Hamilton.  (What would we do without medical people?)  It seems, however, that it was Wallich’s seed that arrived at the Liverpool Botanic Garden in 1815 and at the Royal Botanic Garden, Edinburgh in 1821.  Arboreum had been ‘discovered’ by a Captain Hardwicke in 1796 on the Sewalic Mountains of India.  This species and thosmsonii were the first large red rhododendrons to be seen by covetous, grasping Western horticulturists.  Readers are referred to Davidian, ‘Rhododendron Species’, Vol. 11 for a fuller account of arboreum’s introduction.


Arboreum, with its several sub-species, has a very extensive, patchy (disjunct is, I think, the proper  word) distribution throughout India, the Himalayas and neighbouring China.  There are remarkable isolated populations in southern India and in Sri Lanka.  Some of these forms, usually with red flowers are not hardy here and are only suitable for semi-tropical locales.  On the South Island of New Zealand we saw specimens that were centenarians.  It has also become naturalized in Jamaica.


Local gardens have some notable, but still relatively young, examples of the species; the arboreum ssp. cinnamomeum in Dora Kreiss’s garden comes prominently to mind.  There are some good plants of perhaps the most famous of all arboreum hybrids – ‘Sir Charles Lemon’ – at the Finnerty Gardens.  My premise that more use could be made of arboreum rests mainly on the few plants I know well – those in my own garden.  In the deepest, darkest days of winter when only the odd hellebore and camellia and viburnum are in flower, ‘Rosamundi’ and ‘Lee’s scarlet’ and ‘Nobleanum’ are glowing photon-emitters of warmth.  Half of their genes come from arboreum.  Many gardeners are disappointed when the ‘Christmas Cheer’ they have cherished and coddled for a few years, blooms in late March.  It was baptized as ‘Christmas Cheer’ in the 1820s when those who could afford to buy rhododendrons had large conservatories and this plant could be forced to bloom for Yuletide decoration.  My point is that we need more of these dark day dazzling denizens.  There is a strong demand for bloom in the winter months.


This early season blooming can be obtained from arboreum and this characteristic along with colour selections that are clean and clear; indumented foliage, that is crisp and precise and resistant to weevils and mildew; and good plant habit, make arboreum an attractive parent.  The Social Services Agency for Horticulture will approve.


The subspecies of aboreum – nilagiricum, I have never seen.  It may not be hardy here but its hybrid, ‘Noyo Chief’ , and that plant crossed with yakushimanum, to give ‘Noyo Brave’, are contemporary garden-sized plants with outstanding foliage and good flowers.  Even better is the New Zealand hybrid ‘Rubicon’ which is ‘Noyo Chief’ x ‘Kilimanjaro’.  This has only 25% arboreum in its lineage but (proving the importance of grandparents) this is evident in the foliage.  ‘Rubicon’ may well be the best compact red rhododendron yet developed for gardens in our area.  It is an April bloomer.  Arboreum ssp. nilagiricum has been reintroduced within the last ten years.   Keen growers and hybridizers should be on the lookout for this plant.  Some of the newer introductions could be hardier.


The red-flowered plant of arboreum that I have is now about 12 or 14 feet tall and 30 years old.  The leaves are not as large as the two-toned pink form (yet unbloomed for me) and have silvery indumentum.   The really outstanding feature is the reliability of blooming and the duration of the bloom.  Last year it was in flower for a full two months.  My second flowering plant is pink and it had a somewhat later but almost as prolonged bloom.  The plant had its first  flowers two years ago and these were miserable, small, recycled looking things.  After such a dramatic improvement with the second blooming, I have hopes that the show may be even better this coming March.  I had bloom on ssp. delayvayi for the first time last year and this was a clear primary red.  The habit of the plant is tidily symmetrical and the foliage a notable dark matte green.  This sub-species has had no winter damage during the last ten years, although it is recorded as being a tender plant.  I have also bloomed a white form of arboreum ssp. arboreum.


Already referred to was ‘Sir Charles Lemon’.  This, Cox opines, is arboreum with campanulatum.  It is famous for its cinnamon indumentum.  It is a plant to look up at.  Another hybrid of this parentage from the 1800s which I have recently acquired, also has good foliage and judging from photographs, probably better white flowers than ‘Sir Charles’, is ‘George Cunningham’.  This commemorates, I believe, the Cunningham who ran Comely Bank Nursery in Edinburgh.  He is more notorious for ‘Cunningham’s White’ which could well  hold the record for the most propagated rhododendron ever and likely to remain so, as it is still the best rootstock for grafted plants and used all over the world for that purpose.  Still yet another hoary old hybrid from the mid 1800s which is seldom seen and seems worth the place in a large garden, is ‘Boddaertianum’.  This one originated in Ghent, Belgium at Van Houtte Nursery and commemorates their foreman.  Other foremen have been commemorated such as Faggetter and Wiseman.  Tony James of U Vic is a curator and has a form of williamsianum named for him.  Would it be a good idea to have a Curators’ and Foremans’ bed at U Vic?  I will mention one more early blooming hybrid that I think is overlooked and that is ‘Bibiani’.  This is a Rothschild plant that has blood red flowers in late February.  There is a good specimen in the University Gardens.


I am not a hybridizer, so the following suggestions may have been tried without success or be otherwise unworkable, but in the attempt to get early blooming varieties with bigger pastel coloured flowers, how about using February blooming ‘Heatherside Beauty’, (the records show this as caucasicum crossed with an unknown but that unknown looks like arboreum to me), with the new hotshots like ‘Lem’s Cameo’, ‘Naselle’ and ‘Horizon Monarch’?  Or put pollen from an early blooming white arboreum on these mothers.  For bigger early reds, would a trial of the biggest flowered red arboreum with ‘Markeeta’s Prize’ or ‘Very Berry’ not be worth a shot?  Examination of the ARS Seed Exchange may show there are lots of growers who have had the same idea.  In which case I encourage someone on our Chapter to get the seed and get some plants going.


 The results may not get you to chair the Breeders’ Round Table which is held at every ARS Convention, or get you royalties to match those of the Sultan of Brunei but it will be good for the ego.  Even a rejection, if it gets enough publicity by a famous grower can boost the ego.  I think of the case of the February blooming ‘Praecox’ and that famous plants man A.K.Bulley, (George Forrest’s sponsor).  Bulley refused to have ‘Praecox’ in his garden because of its mauve colour.  ‘Praecox’ had received a commendation from the RHS in 1861 and went on to be crowned with the A.G.M. in 1926 and an F.C.C. in 1978.  Even the Cox family damn it with faint praise.  They write… ‘Rather a harsh unfashionable colour…but flowering too early in the season for the ponticum prejudice to be very influential.’


‘A’ stands for arboreum but it could also stand for Achievement.


STOP PRESS.  The first flower on ‘Nobleanum Coccineum’ was fully out on 28th October.  For the greater good of the cause, this was picked and John Hawkins is storing the pollen for application on worthy mothers later in the season.