Morton Arboretum Bulletin of Popular Information

Vol. 23, No. 5 May, 1948 MORTON ARBORETUM - JOY MORTON · FOUNDER e. BULLETIN OF LISLE, ILLINOIS POPULAR INFORMATION HARDY AZALEAS The lavish Azalea displays possible in milder sections of the country are of course out of the question in this area, but if one wants Azaleas, several species are available which are quite as hardy hereabouts as any of the other shrubs we grow and surprisingly tolerant of our alkaline soils. Rhododendron dauricum, the Dahurian Azalea, or more correctly Rho dodendron, for botanists now classify all Azaleas as such, is one of these, a plant whose performance at the Arboretum contradicts the prevailing idea that, "Azaleas simply cannot be grown here." After watching this specie~ for twenty-one years, during which time we have seen it develop into an upright twiggy bush over six and a half feet tall, we wonder what better proof of its remarkable adaptability is needed? Growing in thin oak woodland, in a location that is well drained and yet never dry, it has had little special care other than a constant mulch of oak leaves and protection from rabbits in winter. Year after year it opens its fragile mauve blossoms, usually simultaneously with the Forsythias, and while oc casionally nipped by late frosts, the buds never show any ill effects from sub-zero temperattJ,re. During the winter just past the mercury dropped below zero at least eleven times, on one occasion reaching -13 °, and yet at the time of writing (April 20) this Azalea is in full bloom, every branch bearing its full quota of fragile, two inch bell shaped flowers. Long pro truding stamens add to their interest. After flowering season is over, good foliage, narrow oval in shape and of bright green, clothes the branches until late fall. In milder areas it is sometimes evergreen. When we learn that the native habitat of this shrub embraces some of the colder regions of Korea, Mandshurica and Northern Japan, it is perhaps not so strange after all that it .should withstand so successfully our climatic vagaries. 17 In usmg this Azalea in landscape plantings any of the pale yellow Forsythias suc.h as "oyata", "japonica saxatilis," or " intermedia pri mulina", if it blooms early enough, will be found to be ideal companion shrubs. Add a grouping of soft yellow Narcissus beneath them, edge the planting with the pygmy purple Iris, Iris pumila atroyiolacea and a stunning picture results. A closely related and equally hardy species which some authorities consider merely a variety of "dauricum" is the Korean Rhododendron, Rhododendron mucronulatum. The basic difference between this and the Dahurian form seems to be in the foliage, "dauricum" often being ever green or semi-evergreen, while "mucronulatum" is deciduous. We have not found it to be earlier flowering here nor noticed any appreciable difference in the size and coloring of its flowers. From a landscape point of view both species are about on a par, but the fact that "mucronulatum" is more easily obtained perhaps gives it a slight advantage. About the middle of May, if the season is normal, we can expect the fragrant blossoms of the Korean Yodogawa Azalea, Rhododendron yedo· ense poukhanense. This is the common 'wild. Azalea of the grassy slopes and thin pine woodlands of southern Korea .and has proved itself a most adaptable and free flowering plant. Lower growing than: the other two, it forms compact rounded bushes_which with us have not exceeded a height of three and one half feet since being planted in 1927. The new foliage unfolds a pleasing bronzy color furnishing interest until the large, single, fragrant flowers of lilac purple make their appearance. Arranged with plenty of green foliage they are not in the least discordant and may be successfully combined with most other late May flowers. In this area the foliage is usually semi-evergreen, changing to purplish bronze in late autumn. The best red Azalea for this area is Rhododendron obtusum Kaempf eri, called Torch Azalea because of the brilliance of its carmine or scarlet pink (usually with a salmon tinge) flowers. Japanese in origin, an inhabitant of thickets and woodland margins of the central and northern sections of that country, it was first introduced into the United States in 1892 by Professor C. S. Sargent, who considered it one of the most valuable foreign plants ever brought to New England. Notwithstanding the hardiness of the plant itself, the flower buds of the Torch Azalea are often injured by sub-zero temperatures. This accounts for the scattered 18 Specimens of the Dahurian Azalea, Hhod od endron dauricum planted in the Arboretum in 1927. bloom this year. Inasmuch as the flowers fade easily in full sunlight, a planting site protected by light woodland is recommended. In just such a location our collection boasts two erect branched specimens six feet tall. This species is deciduous in the north, its ·foliage coloring bright red orange in fall. Another bud tender species, which incidentally is one of the finest of all Azaleas, is the lovely p:nk blossomed Royal Azalea, Rhododendron S chlippenbachii, named for one Baron von Schlippenbach, naval officer and traveler. Native of Korea, northeastern Manchuria and limited sections of central Japan, the plant seems to be hardy enough, provided a well drained location is chosen for it. It is the possible injury to the buds by low winter temperatures which limits its use in colder sections of the country. When it does bloom well it is a joy to see, the large slightly fragrant funnel shaped Hower of clear pink, without the slightest trace of magenta, appearing freely about the same time the foliage is expanding. The leaves are very attractive in their own right, being soft yellow green 19 in color. In autumn they change to orange and yellow tones. The habit of this species is commendable, too, being rounded and compact; Apt to be even more eccentric in behavior is the variable Chinese Azalea, Rhododendron mo/le, known for its tolerance of summer heat and drouth and ability to thrive in soils of only slightly acid reaction. It definitely lacks the hardiness of the others, however, and although variations of it have been successfully grown elsewhere in this area, * we have never been able to keep it longer than a few years. The type species has showy yellow flowers but the many hybrids of it offered by the trade as varieties bear blossoms ranging in color from salmon rose to apricot, terra cotta and yellow. In addition to the Azaleas already mentioned, we are growing plants of several of the Gable Hybrids, a promising strain produced by Joseph B. Gable of Stewartstown, Pennsylvania. These hybrids represent their introducer's efforts to produce a hardier strain of the Japanese type of Azalea in better form and color than has heretofore been available. Two varieties, "Elizabeth Gable" and "Herbert", which have been on trial since the spring of 1942, have reacted very favorably to local conditions. Both are late May bloomers, "Elizabeth Gable" with profuse rose pink flowers and "Herbert" with more purplish blooms brown dotted at the throat. In this area all Azaleas demand a well drained planting site, preferably one which does not dry out in summer, protection from strong winds, both summer and winter, a specially prepared soil mixture of neutral or acid reaction and a constant mulch of oak leaves. In our April, 1947 bulletin entitled, "Hints on Establishing Finicky Plants", detailed in structions were given for preparing soil for acid loving plants. E. L. Kammerer * There is a mature specimen of Rhododendron molle six feet tall and over 25 years old in near-by Warrenville, Illinois, which blooms regularly year after year. BOARD OF TRUSTEES MRS. JOSEPH M. CUDAHY, Chairman MARK MORTON STERLING MORTON WIRT MORTON JOSEPH M. CUDAHY EDWARD H. STEARNS MRS. ERNEST A. HAMILL II JOHN A. HOLABIRD DANIEL PETERKIN, JR. * * CLARENCE E. GODSHALK E. LOWELL KAMMERER* JOHN VAN GEMERT Director Arboriculturist Prop4g4tor PUBLISHED MONTHLY BY THE MORTON ARBORETUM, LISLE, ILLINOIS SUBSCRIPTION FEE $1.00 A YEAR SINGLE COPIES 10c 20 .

Load more