JARS v40n2 - California Rhododendron Hybrids

California Rhododendron Hybrids
Parker Smith
Sebastopol, California

The past thirty to thirty-five years have seen the creation of approximately 130 named rhododendron hybrids by Californians. This is not a large number compared to the quantities produced in other parts of the country, but many are unique and most are ideally suited for California's rhododendron growing environments.
Their adaptability to other mild climates has not been widely tested, although a few have performed well in the Pacific Northwest and others are being tried in Australia and elsewhere. Cold hardiness has seldom been a consideration in their selection since most rhododendron growing areas in California are coastal and experience only a few degrees of frost. Heat tolerance, defined as being able to perform under high temperatures and dry air conditions, has been a factor in the development of only a few of these hybrids. Coastal climates have their temperatures moderated and their humidity increased by the presence of ocean fog that comes ashore during most of the warm weather months. Although they may not be hardy, many of the smaller growing plants, derived from the Maddenia , Boothia , Moupinensia and Tephropepla subsections, plus the Vireyas , make excellent container specimens for the greenhouse, sun-room, or other well lighted indoor space during the cold season and for the patio, terrace or deck during the rest of the year.
Large flowered elepidote hybrids have not been the major direction of hybridizing in California but several significant hybrids have been created. Two of the best known of these are 'Ruby Bowman' (deep pink) and 'Stacia' (lavender blue), which both have fortunei as one of their parents. 'Burgundy' ('Britannia' x 'Purple Splendour') is appropriately named and blooms well in the shade. The influence of elliottii is present in two outstanding hybrids of this type, 'Jim Drewry' (brilliant red) and 'Helen Druecker' (dark pink). Less known, but worthy of greater distribution, are 'Fort Bragg Glow' ( elliottii or griersonianum hybrid), a glowing pink, and 'Lucy's Good Pink' ('Ruby Bowman' x griersonianum ), a medium pink shading darker in the center. John Druecker, and the late Dr. Paul and Ruby Bowman were responsible for the creation of these hybrids in the Fort Bragg area of California.
Although members of the Arborea subsection generally perform well in our climate, only a few hybrids have been developed to take advantage of their adaptability. 'Noyo Chief'( arboreum ssp. nilagiricum hybrid introduced by the Bowmans) is an outstanding plant both for its crimson red flower trusses and the highly glossy, textured, deep green foliage. Allan and Ethel Korth of Santa Cruz have named two early blooming hybrids with brilliant red flowers. The result of a cross of 'Cornubia' x 'Red Olympia', 'Blazing Glory' and 'Prairie Fire' appear to be very promising hybrids. 'Kerrigan's Early Red' is another Cornubia hybrid by Howard Kerrigan of Oakland. It is a cross with 'Vulcan' and has not yet been distributed widely. Not in the Arborea subsection, but blooming at the same early date, is a hybrid of unknown parentage called Lukiangense hybrid. It was grown at the University of California Botanical Garden in Berkeley and forms a six foot shrub covered with rich pink trusses in January or February.

Lukiangense hybrid
Lukiangense hybrid grown by UC Botanical Garden,
Berkeley of unknown parentage, one parent likely to be
R. lukiangense
(not registered).
Photo by Parker Smith

Little has been attempted with the blue-purple flowered lepidotes but those few that have been named are very useful plants. Howard Kerrigan crossed 'Blue Diamond' x augustinii , Exbury form, and two of the offspring were named, 'California Blue' and 'Pacific Blue'. Both are heavy flowering (deep violet blue) plants with foliage and height midway between their parents. 'Little Imp' is the creation of Stewart and Audrey Barber of Sebastopol, and is a cross of impeditum and 'Blue Diamond'. It is a low growing, spreading plant that is easier to grow than the species itself and provides a dependable display of blue violet flowers against silvery grey foliage. 'Little Augi' (Barber) is another hybrid in this category and a cross of 'Little Imp' x augustinii . Midway between its parents in most respects, it is just becoming available.
The vast majority of rhododendron hybridizing in California has concentrated in the Maddenia and closely related subsections. These plants thrive in our coastal climates and provide color from January to July while putting forth a wide range of pleasing fragrances. 'Else Frye'(Bowman) was one of the earliest introductions and remains one of the most dependable and popular. It has very fragrant, medium sized flowers that combine pink and white with a yellow throat. Dark green, textured foliage that looks good all year typifies this hybrid and most others in this group. The Bowman's 'Reine Long' ( taronense x 'Else Frye') is very similar in flower but possesses a stronger growth habit and slightly superior foliage. Another early white is 'Winter Lights' ('Bric-a-brac' x scopulorum ) which is a midsize plant that covers itself with flowers. lt is a recently registered hybrid by Bill Moyles of Oakland. A fast, upright growing, mid-season white with a yellow throat is named 'Charles O. Phillips'. Several other hybrids with fragrant, white flowers have been developed in the Eureka area using 'Else Frye' crossed with johnstoneanum . They include 'Doctor Richard Anderson', 'Humboldt Sunrise', 'Super Jay', and 'Quala-A-Wa-Loo' (Anderson/ Braafladt).
Large flowered whites are available in 'Bill Massey' (syn. 'Nutberger' by Vaerlen/Druecker/Trillium Lane Nursery ) and 'Parlevous' (Parle). These are both from the cross of ciliatum var. x bergii x sinonuttallii and have moderately large, clean, textured foliage on medium height plants. 'Alpine Snow' (Richards/Spini) combines three species ( lindleyi , dalhousiae , taggianum ) to form a tall, upright plant with large, fragrant trusses of white flowers with yellow throats. Equally large and fragrant flowers, but with a ruffled edge, are present on 'Virginia Stewart' (Kerrigan/Stewart) which is also a more compact shrub than the previous hybrid. This outstanding cross of 'Countess of Haddington' x nuttallii is one of several hybrids in this group that has the added attraction of red, peeling bark from an early age. The best known of the large, white flowered hybrids of this type is 'Mi Amor', the lindleyi x nuttallii cross made by Fran and Maury Sumner of San Francisco. It has very large, nuttallii -type flowers in 6-7 flowered trusses that are highly fragrant. The foliage is large and nicely textured on a 6-8 foot upright growing shrub.
'My Lady' ('Foresterianum' selfed) and 'Martha Wright' ( burmanicum x 'Fragrantissimum') are two more Sumner hybrids that introduce additional color into the fragrant flowers. The former has elegantly shaped flowers that are white with pastel shades of yellow, orange and pink in the throat. It is also an outstanding foliage plant that forms a well branched shrub 4-5 feet tall, spreading wider. 'Martha Wright' has fragrant flowers of a soft, creamy color and texture, on a more open growing shrub. Howard Kerrigan made the reverse cross of this last hybrid and appropriately named the resulting selection 'Heaven Scent'. Another cream colored hybrid is 'Lake Lorraine', created by Bob Scott of Kensington, from a cross of burmanicum , Cox form and the rare species, cuffeanum . The color of the expanding flower buds is a special bonus of this medium height hybrid.

R. cuffeanum KW #21909
R. cuffeanum KW #21909, rare species
in the Maddenia subsection.
Photo by Parker Smith

Introducing additional color into this group of hybrids with all Maddenia parentage is another Bob Scott hybrid named 'Rose Scott'. Its parents ['Else Frye' x ( johnstoneanum x cubittii )] are known for their fragrances and this hybrid features a powerful, pleasing fragrance, easily detected twenty feet away in the garden. 'Starbright' ('Else Frye' x rhabdotum ) by Scott is a hybrid with large white flowers having pink stripes and a deep yellow throat. Yellow is the dominant color in a similar Scott hybrid named 'Butterhorn' ('Eldorado' x rhabdotum ) and in the Bowman's' 'California Gold' ('Else Frye' x 'Eldorado'). Both of these large yellows have some pink on the outer edges or back side of their flowers. They do not form the best shaped plants in this group but are worth growing for their outstanding yellow flowers. A more shapely plant with denser foliage but lighter yellow flowers is 'Owen Pearce' (Sumner). This 'Saffron Queen' x burmanicum cross forms an excellent, heavy flowering, 3-4 foot spreading shrub.

R. 'Owen Pearce'
'Owen Pearce' ('Saffron Queen' x R. burmanicum ), hybridized
and registered by Fran & Maury Sumner, San Francisco.
Photo by Parker Smith

Colorful flowers on low, compact plants have been obtained by making crosses between Maddenia species or hybrids and members of the subsections Boothia , Tephropepla , and Moupinensia , particularly the species xanthostephanum , leucaspis , chrysodoron , and moupinense . Most of these species are very early blooming, have high quality foliage, and in a couple of instances, colorful new growth. 'Conchita' and 'Sabrina Adler' are two plants of the same parentage, ciliicalyx x moupinense , crossed by different hybridizers (Druecker and Scott, respectively) resulting in colorful, very early blooming pinks. 'Conchita' has very fragrant, flat-faced flowers while 'Sabrina Adler' is a more dense, better foliaged plant. Both have colorful new growth (chocolate on 'Conchita') and red, peeling bark. 'Pink Fairy' (Kerrigan) is also an early, low growing pink resulting from the cross of 'Cilpinense' x 'Praecox'. 'Millicent Scott' (Scott) has small, early blooming flowers that are pink and yellow resulting from the interesting cross, racemosum x 'Saffron Queen'.
'Meadowgold' ( burmanicum x 'Lemon Mist') and 'Prairie Gold' [('Eldorado' x leucaspis )x 'Lemon Mist')] are two of Bob Scott's low growing, yellow flowering hybrids. The former has deep yellow trusses on a glossy leaved 2-3 foot shrub. The latter is even lower growing and spreading with medium yellow somewhat pendulous flowers. Two other good yellows, with no Maddenia parentage, are 'Lemon Mist' ( xanthostephanum x leucaspis ) by Scott, a 2-3 foot tall by 4-6 foot wide shrub that covers itself with light yellow flowers in early April, and 'Goldilocks' (Karrigan), a xanthostephanum x chryseum cross, which has smaller but deeper yellow flowers and fine textured foliage on a low growing plant.
'Helen Scott Richey' (Scott) is a February blooming, 2-3 foot tall hybrid [( racemosum x moupinense ) x mucronulatum 'Cornell Pink')] with semi-deciduous foliage and pink flowers. 'Pink Snowflakes' ( racemosum x moupinense ) is another outstanding Scott hybrid with its red flower buds opening to cover the 18 inch tall plant with white flowers having pink tips and a red blotch. It blooms in February and its flowers are followed by glossy, dark green foliage. Another unusual hybrid of moderate stature is 'Robbie' ( cinnabarinum var. roylei x yunnanense var. chartohyllum ) by Dr. John and Fleurette Evans of Oakland. This has light lavender pink flowers that tend to darken with age. Also from this garden is 'Murial Giauque' ( maddenii x cinnabarinum var. roylei ), a large shrub with flowers that contain a blend of pink and salmon tones. Named for Mrs. Evans, 'Fleurette Evans' (Moyles), is a result of the hybrid 'Seta' being selfed. It forms a more open pink flower than 'Seta', and is very early blooming.

R. zoelleri x 'Taylorii'
R. zoelleri x 'Taylorii', hybridized by
Pete Sullivan, San Francisco (not registered).
Photo by Parker Smith

This is only a sampling of the hybridizing efforts by Californians. About 50 of the named rhododendron hybrids from California are Vireya hybrids and many more unnamed ones are being watched. Also, much has been accomplished with hybridizing evergreen azaleas by several individuals (Kerrigan, Nuccio, Barber, Brooks, etc.). There are even some interesting deciduous azaleas that have been created in California that are waiting to be named. This subject will be explored in much greater detail at the 1986 Western Regional Conference of the ARS which will be hosted by District Five(California) at the Holiday Inn, Monterey, California on September 26th, 27th and 28th. The illustrated talks, the photo exhibit, and the plant sale will all emphasize California rhododendron and azalea hybrids as well as the species and other hybrids that perform well in our varied climate. The speakers will include experienced hybridizers, gardeners and nursery owners. The program and pre-registration form will be in the next (summer) issue of the Journal or information can be obtained by writing the registrar, Mr. Tom Wynn, Sunnyvale, California.

Parker Smith, Alternate District Director for District 5, is a landscape architect by profession.