Report from the Morris Arboretum Test Garden
Henry T. Skinner, Curator, Morris Arboretum
A major interest in rhododendrons and azaleas has centered at- the Morris Arboretum of the University of Pennsylvania (in Chestnut Hill) for several years. For the East coast the climate of Philadelphia permits cultivation of a fairly wide range of species and varieties, from the "ironclads" to less hardy Fortunei hybrids and kurumes as are otherwise reasonably at home in Washington or ocean tempered Long Island and Cape Cod. The Morris Arboretum is also fortunate in having some seventy acres of acid clay to gravel loam soil underlain by mica schist in an area of varied topography and well suited to the cultivation of ericaceous plants.
Many azaleas and rhododendrons were planted in earlier days by Mr. John T. Morris, including several Japanese varieties of large present proportions and this collection has been greatly augmented by several hundreds of seedling-raised species from the European Botanic Gardens, the earlier Rock collections and s0 on, as well as by numerous horticultural varieties from, diverse sources. Reports upon the behavior of certain of these plants and plant groups have appeared in the Morris Arboretum Bulletin from time to time.
When the Morris Arboretum was established as a Test Garden of the American Rhododendron Society some two years ago the program of assembling lacking species and varieties received a renewed impetus, resulting in the acquisition during 1950-51 of some 44 new species for testing purposes, 48 hitherto unrepresented named evergreen hybrids and nearly 400 additional azalea varieties, largely in the Glenn-Dale-Kurume classes, though also including additional Ghent, Kaempferi, Chugai, mucronatum and Vuykiana hybrids. The species have been grown from seed but a majority of the hybrids other then those from the Bureau of Plant Introduction, represent most welcome donations from a few especially interested nurserymen. All such plants as these are handled by routine methods, according to size, before permanent placement in a selected area for each group where the individuals can be observed and rated for horticultural merit and performance. So far as the species are concerned such "routine methods" include one year in the cool greenhouse where the seedlings are transferred from seedling flats to three inch pots, and 1-2 years in prepared beds in the lath house before final planting in permanent quarters which may be a semi shaded bed, a rock garden or rock moraine according to type and likely requirements. No special winter protection is ever provided so that the weeding out process of tender types starts in early occasionally, perhaps, a little earlier than is altogether desirable. Recent winters, however, have been reasonably mild here in the East.
Newer azaleas in the obtusum-mucronatum-indicum complexes embracing principally the Kurume, Gable, Glenn Dale and Merritt hybrids - three plants to a variety and on a block planting system - are under special test for comparative hardiness and horticultural merit in a cooperative project with Mr. James S. Wells of the Koster Nursery Company of Bridgeton, N. J. This planting duplicates a similar one at Bridgeton for the purpose of providing a check of results and conclusions arrived at in each locality. The winter climate is a little more severe in Philadelphia and a bottomland site in fairly full sun provides a good test of performance. Approximately 550 clones are at present represented in. this test area and the first significant appraisals should be forthcoming during the current season.
A Trial Garden area has been set off to receive new hybrid rhododendrons officially entered for testing purposes under supervision of the American Rhododendron Society. Test plants will be welcomed for this area but no entries have been received to date.
Of no especial connection with test projects but of possible interest to members of the Rhododendron Society is a research project underway at the Morris Arboretum in the form of a comprehensive geographic and cytotaxonomic study of our native American azaleas, exclusive of R. canadense and vaseyi. It is a cooperative undertaking between the University of Pennsylvania and the Academy of Natural Sciences in Philadelphia in which the objective is to secure far more information than is at present available concerning the constitution, behavior, and evolutionary relationships of these azaleas, that this understanding may find eventual application in a reappraisal of their present taxonomy. Such a project involves detailed study of herbarium specimens on file in the major herbaria of the country. This study was partially completed last year. During the spring and summer of 1951, and using "mass collection" techniques, an additional 89000 specimens were secured by the writer on a continuous 25,000 mile journey from New England to Florida, Texas and Arkansas from March 18 to the 15th of August. Besides herbarium specimens, upwards of 500 plants of representative and unusual forms were returned to the Arboretum for cytological and genetic study and eventually for horticultural breeding purposes within the group.
This research project has been made possible with the help of a grant from the American Philosophical Society added to contributions from a few interested individuals. A further grant from the same source will enable the Arboretum to secure the additional assistance of Dr. Hui-Lin Li as Research Associate commencing May 1st this year. Dr. Li is a graduate of Yenching University, with an outstanding record in the field of taxonomic and geographic botany, gained both in China and at several institutions in this country He will concentrate initially upon a chromosome survey of these azaleas to throw light on relationships and evolution. This project can scarcely be completed in two or perhaps even in four years, but it is felt that a thorough undertaking of this sort may eventually prove of very real value in contributing to our understanding of at least one section of the highly confused genus Rhododendron.