Rhododendron Experiences After the Conference
J. Harold Clarke, Ph.D.
In the last issue of the Bulletin, an account was given of the Rhododendron Conference and the tours organized by the Royal Horticultural Society. At the end of these tours the American group visited other points of interest, and the Editor of the Bulletin has asked that I describe scone of the things seen at that time.
A large plant of R. 'Loderi Helen' layered at Knap Hill Nursery
Jim Russell of Sunningdale Nurseries showing bell jar method
of rooting small leafed rhododendrons.
On returning to London, Brigadier Lycett, Secretary of the Royal Horticultural Society, and Dr. A. S. Thomas discussed with me the horticultural aspects of the coming Festival of Britain. Dr. Thomas, who was organizing the agricultural part of the Festival, was interested in our reaction to the rhododendron tour and was wondering whether many Americans would attend such a tour in 1951, at the time of the Festival. There is a possibility that there might be a rhododendron tour, a rose tour, an iris tour, and possibly others at various times during the Summer. My answer was that if the tours were as fine as the one we had just attended, there should certainly be a large group of Americans who would be interested.
Several of us made a brief visit to Kew Gardens where Mr. C. P. Rafill, Vice-Curator, showed us the rhododendron collections. In the large glass house, 600 x 140 ft. and 70 ft. high, there was a fine collection of the Maddeni series including a very fine specimen of R. calophytum. There was also a blooming plant of R. 'Grierdahl'. Mr. Rafill made the cross two years after Admiral Heneage-Vivian had first made this cross between a lepidote and an elepidote species. It was a disappointment, of course, to be able to spend only a short time at Kew Gardens as it is one of the outstanding botanical collections of the world.
We next visited some of the nurseries near Woking. In mentioning these firm names, it should be understood that there are other rhododendron nurseries in England probably just as important and interesting but it happened to be convenient for us to visit these. At the Goldsworth Nursery of Walter Slocock, Ltd., Mr. Oliver Slocock showed us the various collections and the propagating areas. This is one of the larger nurseries with some 500 acres of nursery stock and a nice display garden of rhododendron varieties including several which originated here. The breeding of rhododendrons has long been an important feature at Slococks. The soil was heavy loam to reddish clay and would not impress one as being ideal for rhododendrons. A very interesting feature was the method of handling azaleas for grafting. A number of azaleas are grafted for Slocock in Belgium and being flown over and back by plane, the time required only two hours each way.
Slocock's, as well as certain other nurseries in England, are now giving considerable attention to the so-called Knap Hill azaleas. These were started by the late Anthony Waterer at the Knap Hill Nurseries. They are essentially Ghent type crossed with R. occidentale deciduous with large funnel shaped flowers. At the time of Anthony Waterer's death, the plant material was divided, Slocock obtaining certain lots, the Knap Hill Nurseries others, and other nurseries obtaining stock at that time or later. Mr. Slocock stated that he was inter-crossing the Knap Hill azaleas and obtaining a very uniform lot of seedlings so that very few had to be discarded. He was propagating this type by first grafting on azalea luteum and then getting plants on their own roots and eventually by layering. Three varieties he recommended rather highly are 'Gog', orange, 'Persil', white with yellow spot, and 'Satan', red.
In this nursery, as in the others we visited, layering was the principal method of propagating rhododendrons. This was admittedly slower but seemed to be satisfactory. The layers are down for two years, then taken up and grown in the nursery for two years, after which they may be spaced out and grown another year or two in order to get budded plants for sale.
A flat bladed trowel was used in layering and a large number of plants could be gotten from one mother plant, depending of course on the variety and its tendency to branch. Figure 5 shows an azalea stool bed at Slocock's. Figure 1 shows a large plant of Loderi Helen layered at the Knap Hill nursery.
Slococks were rooting cuttings in frames outside, using heating cable. These frames were covered with old camouflage material for shade. A liberal use was made of mulch in this and other nurseries. This was of particular value this year because of the record breaking drought. Bracken ferns and spent hops were two favor mulching materials.
Mr. Slocock stated that most of the interest in azaleas in England had been in the Mollis types but now the Kurumes are catching on. There is an increasing interest in Macrantha and Kaempferi varieties.
At Sunningdale Nurseries, one of the most interesting features was the method of propagation under bell jars. Mr. James Russell, the proprietor, told us that they often got as many as 500 cuttings of small leafed rhododendrons under one jar. He had 64 of the bell jars in use, a part of which are shown in Figure 2. The jars were coated with some kind of paint inside to provide shade, but there was a small rectangle of clear glass on the north side for inspection purposes. This nursery, like many others, had been permitted to go backward during the war. It is now being cleared out and gotten into nice shape again. The stool beds and nursery blocks here were rather small, hand spaded and interspersed in light woods to provided shade.
Mr. Russell was building a new greenhouse of pre-cast concrete construction. Even the ventilator sash was of concrete. The rafters and other units had been made as slender as possible so that the house appeared to be rather practical although it might cast slightly more shade than wood construction.
At the Knap Hill nurseries we were particularly interested in some of the very old plants. Among others there was a plant of R. catawbiense over 100 years old which was the original importation of this species into England. The nursery is about 200 years old and there were fine specimen trees, one weeping beech covering one-third of an acre. At this nursery we were also informed that the deciduous azaleas had been more popular in England than the evergreen type, but that the latter were receiving more attention now.
Stool bed of Knap Hill azaleas in Slococks nurseries in England
Fig 6: R. hanceanum namum, a beautiful yellow dwarf
in the garden of A. T. Johnston in North Wales
At Windsor Great Park we saw extensive plantings of rhododendrons and azaleas. This estate of the Royal Family comprises about 5,000 acres. It is being developed in large part for public park purposes although the King, who is keenly interested in rhododendrons, gives it considerable personal attention. Mr. E. H. Savill, the agent, is planning to have a fine rhododendron collection for the public benefit which in years to come may approach the size and variety of some of the finest private gardens of the present. An interesting feature was a "stump" garden with oak stumps and large limbs used to retain the soil in narrow terraces, somewhat as stones are often used in rock gardens. The effect was quite pleasing. Incidentally, the oaks on this estate are fine specimens, many of them being "Pre-Conqueror" which means that they were growing before William The Conqueror came to England.
Dr. Bowers and Mr. Grace went with us to Edinburgh, our main objective being the Edinburgh Botanic Garden which probably contains the best collection of rhododendron species in the world. It was amazing to see many species which we would consider as being rather tender, growing so far North. It is hard to realize that we were further North than the Aleutian Islands. Edinburgh is in about the same latitude as North Central Labrador and Central Siberia.
One of the outstanding features at Edinburgh is the rock garden covering four acres, and containing a very fine collection of dwarf rhododendrons. These have been described briefly by Mr. David Wilkie in the last American Rhododendron Society Year Book. Dr. J. M. Cowan and Mr. Wilkie conducted us through the extensive collections. Many of the species, new to us, have great potential value as ornamentals and will undoubtedly appear in gardens in this country at some future time.
The Edinburgh Botanic Garden is not only maintaining a collection of rhododendron species but is carrying on research in various fields affecting the genus, including disease identification and control and propagation. A very extensive herbarium is maintained and the various species of rhododendrons are being re-examined in order that they may be classified more accurately. Sir Win. Wright Smith, the Regius-keeper, and Head of the Department of Botany of the University of Edinburgh, has been interested in rhododendrons for many years and is still actively engaged in supervising the work.
The Botanic Garden also gives courses designed to train men for work as gardeners or as horticulturalist. There are four nine month terms in this training series, one each in propagation; glass house management; outside plant materials, herbaceous; and outside plant materials, shrubs and trees. The boys taking these courses work at regular rates during the day and take their course work at night. Some of the plants in the collection, which 400 to 500 species are very old, dating back to about 1810. There is a large collection of tender varieties under glass.
Through the good offices of Dr. Cowan we were taken about Edinburgh to see some of the many historic spots including Holyrood Palace, Edinburgh Castle including the War Memorial, John Knox's home, the bridge over the Firth of Forth.
After returning from Edinburgh to London, we left immediately for Boskoop, the center of the nursery industry in Holland. It has a population of about 10,000 and boasts some 700 to 800 nurseries which constitute the only industry. The most popular plants in the nurseries are rhododendrons, azaleas, Japanese maples and various conifers. The soil consists of about 30 ft. of peat underlain by sand.
The water in the canals is only about 18 inches below the ground level. Nurseries are worked entirely by hand the soil being spaded rather than plowed. Much of the plant material is grown directly in the ground but extensive use is made of frames and green houses. Mr. Hank Deken, president of J. Blaauw & Company, who is also President of the export group of nurserymen, met us at the train and took us around the nursery section. We could not help noticing the contrast to the English nurseries where the soil was hard and dry, and clay and loam rather than peat. J. Blaauw & Company was formerly the C. B. Van Nes Nursery from which have come many varieties such as 'Britannia' and 'Earl of Athlone'. At the present time considerable emphasis is being given to azaleas. Large numbers of azalea plants are grown from seeds, the better ones being sold as seedlings and the best ones occasionally propagated as clones and named. All of the transportation work is done by boat. In spite of everything being hand-worked, the Dutch nurseries that we saw were extremely neat and well cared for.
After leaving Boskoop we went to Amsterdam by way of Allsmeer, where we stopped long enough to inspect the very modern flower market. There was a large set of buildings covering some acres with concrete floors and roofs supported by steel trusses so that there were large spaces for the moving of trucks. Apparently a large part of the cut flowers and potted plants used in Holland come through this market, arriving by barge and by truck. Sales are by auction. There are four auction rooms, three of which were in use when we were there, one for potted plants and two for cut flowers. The buyers sit on a steep bank of seats, each with a push-button directly in front of him.
The large dial, some 6-ft. in diameter on the front wall, is marked with prices. The auctioneer turns a large pointer by remote control and the buyers bid by pushing a button when the pointer reaches a price they want to pay. Their seat number is registered in the secretary's booth and the sale is completed without noise in great contrast to the produce auctions in this country. Rhododendrons and azaleas were included in the potted plants being sold.
In Holland, as in England, Scotland, and Wales we found that a mutual interest in flowering plants was sufficient to encourage friendship and a lively interchange of experiences.