Rhododendrons for San Francisco Bay Area Gardens
From a Symposium presented at the Meeting of the California Chapter of the American Rhododendron Society, April 28, 1955.
Members of the panel were: Roy L. Hudson of Golden Gate Park, San Francisco, Harry Roberts of U.C. Botanic Garden, Berkeley, Howard Kerrigan of Kerrigan's Nursery, Oakland, Moderator: Dr. Albert C. Daniels, Ross.
Rhododendrons and azaleas offer the home gardener both interesting foliage and lovely flowers in his plantings. The San Francisco Bay Area has most of the essential climatic factors for success with rhododendrons. The temperature range is favorable for outdoor culture of the members of the Boothii, Edgeworthii, Grande, Irroratum, Maddenii and Stamineum Series. Recently many of the various species and hybrids of the Maddenii Series have gained considerable popularity. With some care as to soil, moisture, and shade requirements many interesting cultivated varieties may be introduced into our gardens. Since these come in different flower colors we should find out from the experienced growers in our area which cultivated varieties of these series do the best. in each color range.
Our panel of experts will briefly discuss the newer rhododendrons in local gardens in various colors.
Fig. 36. R. 'White Swan'
R. Henny photo
Of the whites all are agreed the old stand-by is Rhododendron 'Loder's White.' It blooms in early May with a well formed truss of large white flowers. R. 'Doctor Stocker' is also a dependable white. R. 'White Swan' (R. decorum x R. 'Pink Pearl') is a mid-season bloomer (May) that is easy to grow, blooms young and has large flowers which are slightly suffused with pink when they open but later become pure white. R. 'Angelo' and R. 'Snow Queen' are late bloomers (June and July) and for that reason in this area one may find the flowers hidden by new growth.
The Maddenii Series has a fine group of whites for our gardens. Many are new both to our gardens and to the trade. R. 'Forsterianum' (hybrid between R. edgeworthii and R. veitchianum, which is used in Golden Gate Park) has an upright habit, is easy to grow, and may be kept compact in the small garden. R. 'Princess Alice' is a low compact grower with slightly pink flowers. R. 'McNabianum' is a leafy, compact shrub, attractive all the year and has the lovely white flowers with the fragrance common to all the Maddenii Series. R. 'Countess of Sefton' has spectacular flowers, lovely white with some pink veining on the outside. R. 'Countess of Haddington', a hybrid between R. dalhousiae and R. ciliatum, is one of the hardiest in the Maddenii Series. It has tubular white flowers, four inches long and three inches wide. It is one of the most satisfactory rhododendrons for the Bay Area. R. nuttallii has large-flowered heavily laden trusses of rich cream-colored fragrant flowers fading to pure snowy-white. R. 'Fragrantissimum' (R. edgeworthii x R. ciliatum), hardy, with lovely fragrant flowers, tends to become leggy in the shade. It should be pinched back frequently the first two or three years in order to develop a strong compact framework and distribute the growth into more numerous growing tips.
A long list of pinks was discussed. R. 'Sir Frederick Moore,' although it has to reach a good size before it will bloom well, has fine trusses of salmon pink flowers in May. It is considered a late bloomer. R. 'Azor' (R. griersonianum x R. discolor) is also a late bloomer (June) with salmon-pink trumpet-shaped flowers; mature plants reach six to eight feet. Of the Dutch types, R. 'Jan Dekens' is a robust plant with ideal growth habits and beautiful foliage, and has huge heads of rich pink flowers with frilled edges. It is a seedling of R. 'Pink Pearl.' R. 'Antoon van Welie' is a typical Dutch hybrid with strong growth and handsome foliage. It has carmine-pink flowers which hold their color well; they are huge upright conventional trusses, with frilly edged flowers (mid-May). The plants bud young. R. 'Madame Fr. J. Chauvin' is a free blooming plant, a handsome early bloomer, with a well formed truss of rosy-pink, pale center flowers with a deep blotch.
Many new seedlings of R. 'Loderi' (R. griffithianum x R. fortunei) make healthy twelve to fifteen-foot shrubs. They include many of the most outstanding hybrids in cultivation. These bloom at a fairly early age. Such cultivars as R. 'Loderi' var. 'Venus,' var. 'King George,' and var. 'Sir Joseph Hooker' have quite good foliage and are recommended for the large garden areas. They have huge shell-pink fragrant flowers which bloom in May. R. 'Cornish Cross' has loose trusses of varying shades of pink on the same plant. It takes shade, does well in the cool weather, and holds its blooms for ten weeks. Some of the seedlings of R. x 'Loderi' in the University of California Botanic Gardens at Berkeley, are early bloomers and are heavily laden with flowers. R. 'Sarita Loder' is an early pink with loose trusses. It tends to become somewhat leggy. (It is a R. griersonianum cross).
Fig. 27. R. 'Naomi' var. 'Exbury'
R. Henny photo
R. 'Naomi' var. 'Hope' and R. Naomi' var. 'Exbury' have compact growth and have flowers from white to deep pink. They take the place of the Loderis in the smaller gardens.
The R. williamsianum hybrids are useful in our gardens. R. 'Bow Bells' (R. 'Corona' x R. williamsianum) is a low growing compact shrub reaching two to four feet in height. It has an attractive small rounded leaf (the young growth has a striking bronzy color) and its flowers are small nodding pink bells (May). Although it has a short blooming period of but two weeks, because of its slow growing habit, and since it is a lovely shrub all the year long it deserves a place in even the smaller gardens.
Fig. 28. R. 'Moonstone'
R. Henny photo
Other R. williamsianum hybrids of interest are the mid-season bloomer R. 'Olympic Lady,' a small plant, strong grower, with blush pink flowers. (It gives the appearance of a small Loderi). R. 'Moonstone'. (R. williamsianum x R. campylocarpum) has lovely pink tubular flowers (mid-April). It is an attractive small plant of two and a half feet in height. R. 'Temple Bells' should be mentioned. A seedling known as "Sumner #f 1," a cross by our own members, Mr. and Mrs. M. H. Sumner of San Francisco, is a lovely pink. R. 'Royal Flush' (R. cinnabarinum x R. maddenii) has attractive pink forms blooming in May. It is one of the parents of R. 'Lady Chamberlain' and R. 'Lady Roseberry'.
R. 'David' (R. neriiflorum x R. 'Hugh Koster') is easy to grow, has fine habit with rich blood-red flowers (mid May). (It bears resemblance to R. 'Earl of Athlone' but is superior in habit). R. 'Jean Marie de Montague' is a mid-season (May) bloomer with compact growth to six feet and good green foliage. Exceptionally good in Golden Gate Park. R. 'Daphne' is an early bloomer, branches well and is heavily covered with flowers. R. 'Earl of Athlone' is as fine a red as they come. It is found to be somewhat leggy at times but the foliage is excellent and the rounded trusses are of good substance and appear in late April. R. 'Ivery's Scarlet' has the longest blooming period of the reds (November to June), possesses beautiful foliage and compact trusses. R. 'Edith Mackworth Pread' is recommended as a background plant. It looks fine in the bud. R. 'Langley Park' does well in partial shade, never fails to bloom, has a glowing quality flower (the flowers fade rapidly in the sun).
The R. griersonianum hybrids have compact habit of growth and good foliage when in bloom. The flowers, a striking brick-red, are borne in loose drooping trusses. Since all the trusses are never open at any one time these plants are fine for mass plantings, but because of their ragged chlorotic foliage, in spite of treatment, they are not recommended for the home garden. R. 'Elizabeth' (R. griersonianum x R. repens) is considered a "number one". It has large brick-red flowers in late April, possesses a spreading habit, attains a height of three feet, and is easy to cultivate. R. 'Radium' (R. griersonianum x R. 'Earl of Athlone') is a less leggy plant to six feet and has fine flowers (late May). R. 'Damozel', a recent introduction from Exbury, appears to be hardy and has a compact truss. R. 'Vulcan' (R. 'Mars' x R. griersonianum) has the most compact truss and its foliage does not burn. (Flowers in mid-May). R. 'May Day' (R. haematodes x R. griersonianum) does well in the shade as do the other griersonianum hybrids. It is the reddest of these hybrids, flowers appearing in May, and forms a spreading shrub four feet in height.
Of the blue rhododendrons R. 'Blue Peter' is a compact plant to five feet in height with rich green foliage and lavender-blue flowers in early May. It buds up while quite young. R. 'A. Bedford' is a strong grower, which has rounded trusses of large lavender-blue flowers with a large, clear cut blue-black eye in May. R. 'Susan' a campanulatum hybrid flowering in mid-May, is more blue; makes a fine compact plant with attractive foliage. It sports a deep violet blotch. R. 'Blue Diamond' is a medium sized plant that takes full sun, and is considered one of the finest blue-flowered dwarf rhododendrons. It has a long blooming period in mid-April. R. augustinii var. Exbury has early large, deep blue flowers in loose trusses and is the tallest of the blue flowered rhododendrons in general cultivation. R. impeditum, with tiny attractive deep violet flowers, is a dwarf species from the high mountains of southwestern China. It has a spreading habit, a height of less than two feet, and is excellent for rock gardens. R. 'Sapphire' is a low plant with small clear blue flowers and metallic blue-green, aromatic foliage. R. 'Electra' has outstanding blue flowers.
Fig. 29. R. 'Diane'
R. Henny photo
The long blooming period (which begins about the first of April) of the gold and cream flowers of R. burmanicum makes this member of the Maddenii Series of special interest for Bay Area gardens. The plants have neat compact habit and do well in full exposure or in partial shade. R. 'Canary' blooms early with small deep-yellow bell-shaped flowers. It has good compact habit although the new leaf growth sometimes grows over and hides the flowers. R. 'Diane' is a fine plant with lush green foliage and pale lemon-yellow flowers in large trusses which open in May. The plants need to reach considerable size before blooming and require partial shade to be seen at their best. R. 'Damaris' (R. 'Dr. Stocker' x R. campylocarpum) has a compact medium-low habit and large cream-colored flowers in loose rounded trusses. R. 'Mrs. Betty Robertson' has attractive green foliage on a medium compact shrub, and in mid-May has rounded trusses of huge open cup-shaped flowers of rich yellow with carmine markings in the interior. The yellow forms of R. 'Royal Flush' have loose trusses of pale yellow-cream flowers.
R. 'Eldorado' (R. valentinianum x R. johnstoneanum), from Exbury, is a charming low growing dwarf plant with deep creamy-yellow flowers which open in April. The flowers last quite a long while and are fragrant as are other members of the Maddenii Series. R. valentinianum is a low growing shrub with buttercup-yellow flowers which may be seen in the University of California Botanic Gardens. R. johnstoneanum has creamy-white flowers with yellow throats, and is available in the trade.
R. 'Saffron Queen,' although somewhat leggy, stands full wind. It has small deep-yellow flowers and has parentage from both the Boothii and Maddenii Series. Azaleodendron ' Broughtonii Aureum' stands full sun, can be shaped easily, has interesting flowers, and blooms every year. R. 'Butterfly' has well-shaped, yellow bicolored flowers. R. 'Elspeth' of the Campylocarpum Subseries of the Thomsonii Series is a compact plant eighteen inches in height with good foliage and a mass of pinkish yellow flowers early in the season. It makes a good garden subject.
These are but highlights of an animated open discussion and can do little more than indicate a list of good plants for further study. However, they are species and hybrids that have caught the eye of a panel who are familiar with fairly large collections. Many of the plants have already been tested in the Bay Area and are recommended for that reason.
Written from notes taken at the meeting by Donald R. Pratt, M. D. (Editor, Journal California Horticultural Society and Member, California Chapter A.R.S.)