Saratoga Horticultural Research Foundation (SHRF) began offering new trees and new California native plant selections to the California landscape in the early 1950s. At the time, California natives were considered weeds and few were available in nurseries; the newest trees were typified by Modesto ash (Fraxinus velutina), a tree native throughout the South-west that has proven to have several important insect and disease problems, in addition to troublesome structural defects. The concept of selecting superior forms of natives and street trees, evaluating their potential for nursery production, and producing sufficient quantities to make them commonly available, was reasonably new to the California nursery industry.
For fifty-two years, SHRF served the home gardener, the landscape professional, and the nursery industry through research into the best new plants for California’s developing landscape. In that period, fifty cultivars of native and non-native plants were introduced to the nursery industry and the public. We were both intimately involved in the operation of the foundation and began to wonder how the cultivars had fared in the years since their introduction. Did they have some lasting impact on the evolution of the California landscape? Were they still in common use? How adaptable had they proven?
A few years back, we invited a group of landscape architects, retail nurserymen, wholesale nursery people, and landscape contractors who had specific experience with the plants introduced by SHRF, to gather to discuss these and other questions. Our hope was to learn more from them about the acceptance by the industry and the public of the fifty SHRF introductions. Accepting the invitation were Paul Doty, owner of Berkeley Horticultural Nursery; Hank Hellbush, landscape architect, Design Focus, Inc; Ron Lutsko, landscape architect, Lutsko & Associates; Bob Perry, landscape architect and author; Warren Roberts, superintendent (now retired), UC Davis Arboretum; Nevin Smith, author and horticulturist, Suncrest Nurseries; and Barrie Coate, horticultural consultant and former horticulturist, SHRF.
In addition to the rare opportunity to spend two days discussing the relative merits and idiosyncrasies of plants with some of the finest plants people in California, the committee members were able to come to agreement about positive and negative characteristics that are not commonly known or discussed about various plants.
Among the questions asked of the committee were: what was the relative success of a given cultivar in the retail nursery? How successful was it as a wholesale nursery crop? How often was it seen in landscapes? How well did it survive after being installed in the landscape? Committee members were also asked to comment on their experiences regarding each plant’s tolerance of heavy clay soil, alkaline soil, and water chemistry; its tolerance of common sprinkler irrigation systems; its tolerance of full sun and part shade; and any pest and disease problems associated with the plants.
Problems Appear with Time
One of the benefits of observing a cultivar over a period of twenty to fifty years since its introduction is that the excitement and novelty that accompanies the release of a new plant is modified by real garden experience in a broad range of settings (the real world!). In many cases, plant problems that appear in our current experience did not appear until long after introduction, or may have seemed unimportant compared to the benefits provided by that marvelous new plant.
As an example, before ‘Palo Alto’ sweetgum (Liquidambar styraciflua ‘Palo Alto’) was introduced in 1954, a view down into the Santa Clara or Diablo valleys in autumn would not have included any red fall color on deciduous trees. ‘Palo Alto’ and the subsequent cultivars, ‘Festival’ and ‘Burgundy’, provided that variety of fall color for California. They fulfilled a need that Californians had and resulted in the installation of thousands of sweetgums as street trees and garden trees within a brief period of time.
The excitement over this new dependable fall color far overshadowed anyone’s questions about the aggressive, destructive root systems and the quantities of hard, spiky seedpods that they would produce.
A similar story pertains to ‘Raywood’ ash (Fraxinus oxycarpa ‘Raywood’), which was brought to SHRF by board member George Martin from a trip to Australia where, though not native, the tree had become popular in public and private landscapes. The brilliant dark red fall color, the oval upright habit and fast growth, and the ease of grafting or budding in the nursery made ‘Raywood’ ash an instant success. They were planted by the thousands throughout the western United States.
The first problem to appear is one common to most ashes: shallow, aggressive roots. Next came the breakage of main limbs due the genetic characteristic of this tree to produce a crowded cluster of limbs, all emerging from one point on the trunk. Recently, a more deadly problem has appeared: the infection of main branches by an air-borne fungal disease (Botryosphaeria ribis). As a result, ‘Raywood’ ash should no longer be planted
Ginkgos and Maytens
With the introduction of Ginkgo biloba ‘Autumn Gold’, a dependable butter-yellow fall color was added to California’s autumn display. This male (fruitless) form of ginkgo, or maidenhair tree, is a valuable street tree, but most specimens lean at a fifteen-degree angle, and they are slow growing.
Maunsell Van Rensselaer, director of SHRF in the 1950s, had heard of a tall, relatively fast-growing, pyramidal ginkgo in Philadelphia’s Fairmount Park. On visiting it, he met the street tree superintendent to determine if budwood could be collected from this fine specimen, which was to be named ‘Fairmount’. A graduate student from a local college was given the task of collecting the budwood from this particular tree. Unknown to Van Rensselaer, the inexperienced student collected budwood from a number of different ginkgo trees, some of which eventually proved to have been female! The result, of course, was that the budded progeny differed in growth habit from the chosen ‘Fairmount’ parent; some, indeed, produced the smelly fruit for which female ginkgos are notorious. Later efforts to collect the appropriate budwood were successful.
Maytenus boaria‘Green Showers’ is no doubt the most handsome Chilean mayten available, characterized by large (for the species), lush green leaves, and long, weeping branchlets that form a small, evergreen version of the most beautiful of weeping willows. Unfortunately, in some circumstances ‘Green Showers’, like other mayten trees, may produce ever-spreading stands of root suckers surrounding the tree.
In other words, the excitement inherent in the introduction of a new plant may be modified by garden experience. Is this a reason to avoid newly introduced plants? Certainly not! The broad range of plants available to gardeners is the heart of the fascinating field of horticulture that is so alive in the West. Using a plant that is new to the industry will always bear some level of potential for surprise—either positive or negative—but true plant lovers thrive on those surprises.
The committee’s review of each plant’s commercial acceptance produced many predictable results, including the fact that the most commercially successful plants were those whose names are known to most people in the industry, although they may not know that the plants were introduced by SHRF.
Many wholesale nurseries now introduce new drought-tolerant plant cultivars to the industry every year. That could be taken as a demonstration of the success of SHRF in showing the benefits to wholesale and retail nurseries of producing and offering droughttolerant plants.
One of the auxiliary benefits of SHRF’s introduction of California native plant cultivars has been a degree of change, from the gardening public’s lack of recognition of the usefulness of California native plants in the 1950s to today’s assimilation of them into the common gardening vocabulary.
Of the trees introduced by SHRF, many are still produced in large quantities. Although sweetgums of any kind are now being avoided by municipal arborists for street tree use, ‘Palo Alto’ remains the most popular of SHRF tree selections. ‘Burgundy’ has never been as popular as either ‘Palo Alto’ or ‘Festival’, apparently because its dark red color lends a dour note to the garden during already cloudy late fall days
Ginkgo biloba ‘Autumn Gold’ and ‘Saratoga’ are grown in a smaller, but consistent quantity. Since their propagation is more difficult than Liquidambar, most of them are grafted by only a few propagators, who distribute their results to a number of wholesale growers.
Most of the SHRF introductions of Magnolia grandiflora cultivars are still grown in reasonable quantity. ‘Samuel Sommer’ and ‘Russet’ are the most commonly seen, while ‘San Marino’ has virtually disappeared from the trade. Perhaps its small size and slower growth are the reason.
Australia’s water gums (Tristaniopsis laurina and T. laurina ‘Elegant’) have remained a consistent wholesale crop for many years, with nurseries producing larger quantities of them each year.
The most popular SHRF introductions, in order of use, according to the opinions of this committee, are: Arbutus ‘Marina’, Ceanothus griseus var. horizontalis ‘Yankee Point’, Agapanthus africanus ‘Storm Cloud’, Liquidambar styraciflua ‘Palo Alto’, Scaevola ‘Mauve Clusters’, Tristaniopsis laurina ‘Elegant’, Correa ‘Carmine Bells’, Ceanothus ‘Ray Hartman’, and Arctostaphylos densiflora ‘Howard McMinn’.
At the other end of the scale, the least popular SHRF introductions are: Pittosporum brevicalyx ‘Golden Pavilion’, Arctostaphylos ‘Sunset’, Artemisia californica ‘Canyon Grey’, Pistacia chinensis ‘Keith Davey’, Galvezia speciosa ‘Boca Rosa’, Ceanothus ‘Owlswood Blue’, and Rhamnus californica ‘Seaview’.
During compilation of the committee’s findings, it became apparent that some of the many of SHRF’s California native cultivars were more commonly sold by wholesale nurseries to landscape contractors than by retail nurseries to homeowners. Arctostaphylos hookeri ‘Wayside’ and Ceanothus ‘Owlswood Blue’ are examples.
Some interesting comments surfaced in the committee discussions, such as:
Carpenteria californica ‘Elizabeth’, a selection of bush anemone native to the foothills of the southern Sierra Nevada, is most successful when treated like a rhododendron, with highly organic, acidic soils, and regular irrigation.
Arctostaphylos densiflora ‘Howard McMinn’ is usually planted in a space for which it will become far too large. Some other manzanitas, including A. edmundsii, succeed in direct relationship to the rapidity of water movement through the soil and the infrequency of irrigation. Arctostaphylos hookeri seems more tolerant of garden conditions than most manzanitas. Arctostaphylos manzanita ‘Doctor Hurd’ is used primarily by commercial landscape contractors, and seldom by homeowners, in spite of the fact that it is a great plant for unwatered landscapes.
Shearing of most ceanothus is successful in the short term, but eventually results in dead wood and unattractive plants. Ceanothus griseus var. horizontalis ‘Yankee Point’ and C. ‘Joyce Coulter’ each have at least two different forms sold under those names. Ceanothus ‘Julia Phelps’ is spectacular for a few years, after which it suddenly declines, usually from a watermold disease (Phytophthora). Ceaonothus ‘Joyce Coulter’ and ‘Louis Edmunds’ are the least disease prone of the ceanothus.
The surprise “winners” in this evaluation process were, in our opinion, the committee members, who had the pleasure of spending two days together and shared countless emails comparing notes with other knowledgeable plants-people. They were able to find many points of agreement in their assessments of the plant introductions, and occasionally found entirely differing views. Both augment our collective knowledge of these introductions from Saratoga Horticultural Research Foundation.