Series Azalea: Subseries Luteum
Leonard F. Frisbie
In writing about the deciduous rhododendron, which many consider to be a poor country cousin to the more spectacular evergreen sorts, I would like to have it understood that I am not trying to place them on a par with the other Series. With me they very definitely run third place behind the quality evergreen species and hybrids. But they do have a place of importance in our gardens. And we are so absorbed here in the Pacific Northwest with an effort to bring our evergreen collections up to a high standard that we are neglecting this less exciting group.
In the Series Azalea there are three groups of deciduous rhododendrons: the Subseries Canadense; the Subseries Luteum and the Subseries Schlippenbachii. Hybridizers have been busiest with members of the subseries Luteum and this discussion will deal with their work and. with the large number of species in the group. Naturally an article of this sort will merely skim the surface of a very big subject.
The early hybridizers In Holland and England were restricted almost entirely to two species, R. molle and R. japonicum, both from the Orient. Resulting hybrids came to be called Mollis azaleas and the term still persists as a blanket designation for all deciduous hybrids, but it is badly out of date at the present time because a number of other members of the luteum group are being used quite effectively.
The R. molle X R. japonicum crosses produced some very fine varieties. We grow many of the standard named ones in our gardens and they are beautiful plants. Until fairly recent times the color range was limited to shades of orange, red, and yellow. But all limitations seem to have been broken at the present time. Some very interesting plants, from the standpoint of color have turned up in the Puyallup Valley in Washington. These plants were grown from bee fertilized seeds of a selected list of very fine imported Dutch and British Mollis azalea hybrids.
Hundreds of plants were grown and a small percentage were of very high quality. In habit and texture of flowers these were the equal of the parent plants, but some had larger flowers and better trusses. Quite definitely there was a wider range of color among the seedlings than among the parent plants. Some of the intriguing color variations were: Neyron Rose HCC 623, a nice pink; Carrot Red HCC 612/1; Begonia HCC 619/1; a good shade of true Scarlet HCC 19/2, and Apricot HCC 609/1.
I bought three plants from this group that I consider outstanding. 'Signal Light' has the best red color of any deciduous azalea I have yet seen. It is Signal Red HCC 719/3 and there is a blotch on the upper lobe of the corolla that is Capsicum Red HCC 715/1. It is planted next to the Azalea 'C. B. Van Nes' which shows as a poor second to it for color. 'Irish Lass' has a nice truss of flowers that are two and seven-eighths inches across. The color is a beautiful blending of Marigold Orange HCC 11/3, Chinese Yellow HCC 606 and Nasturtium Red HCC 14/1. 'Annie Laurie' has flowers that are two and five-eighths across. The corolla is Begonia (Pink) HCC 619/1. The center is heavily colored with Aureolin Yellow HCC 3/3. There is a large blotch on the upper corolla of Chinese Yellow HCC 606. All three of these varieties are on trial at Wisley in England.
Quite a lot of fertilized seeds from these plants have been grown to blooming size and, as yet, no plant has appeared that is near the parent plants in quality. A lot of speculation can be indulged in right here, but it would not be profitable. But I do have one considered opinion; the quality of a hybrid will decrease in ratio to the number of generations the parent plants are removed from the original species. That is offered as an opinion based upon, limited experience and observation. But, it is my firm belief that we can and should do more work in the Pacific Coast country with hybridizing azaleas. If the parents are selected carefully and with intelligence. I believe that some very good and unusual results will be obtained. But the hybridizer will have to have the patience and facilities to grow a great number of seedlings.
The most exciting development in deciduous azaleas to date centers around the R. occidentale crosses and the Knap Hill hybrids. Unfortunately my first hand experience with flowering size plants has been limited to one variety, the Knap Hill 'Goldfinch'. I think that it is far and away the best I have grown in a yellow of this class. The color is rich and heavy. It does not thin out to white as the flower ages. The texture of the flower is heavy and durable. I have imported a respectable number of the best named varieties of these and hope to have a nice collection in flower before many years. The development of this strain goes back many years and stems from the incomparable work of Mr. Anthony Waterer. The plants are vigorous growers once they have survived the, hazard of importation, but I find that I lose a higher percentage of these than the evergreen Rhododendrons which I import.
The Knap Hill azaleas have a heavy strain of occidentale in them and it is well to know that Mr. Waterer used this native American species quite' freely. Others have been busy with occidentale. The results show huge flowers and a fine color range, but my own close observation and study of these is something I am looking forward to in the future. In Washington and Oregon we live next door to or with this important species in its native habitat. We have not made a systematic effort to collect its forms nor have we taken advantage of the opportunity to make a comprehensive study of it. That is something I would like very much to see encouraged by The American Rhododendron Society. I believe a thorough effort along the maximum potential of this fertile these lines can be helpful in realizing deciduous rhododendron.
My membership in The New Zealand Rhododendron Society has brought me some information about the work the late Mr. Edgar Stead of Christchurch did with crossing deciduous azaleas. I have quite a number of excellent color slides of his plants and they are of a very high quality indeed. Here, again we find an American species featured in another land than ours. This time it is R. calendulaceum. He succeeded in getting a very fine color range and a variety of flower forms. Many of his plants have large globular trusses. I am indebted to Dr. J. S. Yeates, Head Botanist, Massey Agriculture College for the photography and it is very good. He furnished fine pictures of individual flowers and close-ups of trusses that make valuable studies. Mr. Stead used the deciduous azalea quite effectively as landscape material.
There are a number of native American species of the Subseries Luteum that are entirely unfamiliar to us here on the Pacific Coast. We have plans, in the Tacoma area, for a public planting of rhododendrons and the first unit will be a complete collection of American species. I am looking forward to the day when we can have general distribution in this section of the following very fine members of Subseries Luteum: R. alabamense, R. atlanticum, R. austrinum, R. cumberlandense, R. prunifolium and R. roseum.