Some Notes on the Maddenii Series
C. P. Raffill, Curator Royal Botanic Garden, Kew
R. ciliicalyx is one of the finest and easiest grown of all the Maddenii series, as it grows in a soil with a good percentage of loam. The bulk of the Maddenii series are fastidious on their own roots, but they all thrive amazingly on stocks of the old R. ponticum and anyone unable to persuade this rhododendron to grow should try the effect of grafting it on this old European species.
That amazingly fine inflorescence of R. taggianum shown by Mr. Del James (illustration American Rhododendron Society Bulletin vol. 3, no. 3, July 20, 1949) was the result of grafting R. taggianum on to R. ponticum, and by doing so increased its capacity, in other words gave it a pig's stomach. R. ponticum has a wonderful constitution and has a large and wide root system. For about 30 years I had a very large plant of the species R. nuttallii (which has the largest flowers in the genus) and this plant was grafted by me on a young seedling plant of R. ponticum. When it was about four or five years old from being grafted it used to have regular batches of large and many flowered bunches of massive and fragrant bloom. Frequently it produced nine huge flowers on a single head. Likewise I think the flower head of R. taggianum shown by Mr. James, the finest I have ever heard of, is responding to the same treatment.
A near ally to R. taggianum is R. dalhousiae, and this does very well on R. ponticum. I have a 35 year old plant planted out in a cool house which is 10 feet in diameter and about the same in height. It also is a lovely sight every year. It regularly sets seed pods and I usually remove all of them except about two or three pods and these I distribute to persons interested in them. These long tubular rhododendrons have a charm and beauty all of their own. That they are faddy and of weak constitution cannot be denied, for most of them are inclined to be epiphytes. However it is easy to get them all to graft on R. ponticum and so save the trouble of coddling them.
The rather extraordinary hybrid of R. 'Grierdal' I find will also graft easily on R. ponticum. It is a most distinct and remarkable hybrid. The first time I made the cross I got good pods and plenty of seeds. I have tried again to get a cross for another batch of seedlings for the last four or five years, and have failed to secure any seeds. The original R. griersonianum plant that I used for the cross is dead and I am inclined to think it was a clone and possibly a tetraploid.
I must again mention R. ciliicalyx. The true R. ciliicalyx is an easy grower and free flowering plant with large flat or saucer shaped bloom of a blush or pinkish white, sweetly scented. It ought to thrive on the Pacific Coast in sheltered locations, for it is a plant from Western China. I have plants of it over fifty years old, which were raised from seeds collected in Yunnan by Roman Catholic Fathers about 1887. The seedlings vary slightly and some have wavy petals. I have selected a very fine large form out of the seedlings, and this plant is most prolific in flower.