QBARS - v26n2 Dexter Rhododendrons: Their Past, Present & Future

Heman A. Howard, Horticulturist
Heritage Plantation, Sandwich, Massachusetts

Dexter rhododendrons
FIG. 25.  Mass planting of original Dexter rhododendrons in
woods along bank of Shawme Lake. Many of these
plants are over 40 years old.

For nearly a half century the name of Charles O. Dexter has been synonymous with fine rhododendrons, the likes of which in most cases were not known to be hardy in this section of the country prior to Mr. Dexter's time. In 1921 Charles O. Dexter, a New Bedford textile manufacturer then 60 years old, purchased a tract of land consisting of 76 acres in the town of Sandwich, Massachusetts. We are told at that time this was a run-down farm consisting mostly of native woodland  - predominately pitch pine, black and white oaks, and black locusts intermingled with some old white pines.
Mr. Dexter's first horticultural interest at his new home was in the growing of cultivated blueberries. Very shortly Mr. Paul Frost, a Boston landscape architect, was hired. Soon many carloads of rhododendrons, mountain laurels, pieris, Carolina hemlocks and other native plants arrived from North Carolina. At this time the Farquhar Nursery located in Barnstable, about ten miles away had many unusual Asian rhododendrons for sale. These plants had been received from the Robert Veitch Nursery in Exeter, England. Several plants were purchased by Mr. Dexter and it is believed these were the plants first used in his breeding program. It is also believed by some people that a few of his original plants came from the estate of Charles S. Sargent, then director of the Arnold Arboretum of Harvard University.
It was not long before other botanists, including Dr. Leonard Ross and Ernest "Chinese" Wilson, a world renowned plant collector for the Arnold Arboretum, gave Mr. Dexter rhododendron plants and cuttings as well as pollen collected in Europe and Asia. According to Dr. Clement Bowers, Mr. Dexter was an excellent hybridizer and propagator, developing many new techniques in the growing of rhododendrons. In a very few years he was raising between five and ten thousand seedlings a year.
Mr. Dexter rarely kept records of his crosses in writing. Consequently, the percentage of his hybrids were never known for certain. To complicate matters more, the actual source of his parent plants or pollen was not known for sure, even by himself. Seedlings grown from foreign source seeds often varied considerably, proving they too were hybrids. Some of the exotic species used in his program included R. haematodes , R. griffithianum , R. fortunei , R. decorum and R. discolor , plus several known cultivars.
Mr. Dexter was very selective in his choice of parent plants. Among his favorites were a R. catawbiense clone called 'Farquhar's Pink', and his own Dexter #8 and #9 which seemed to be his favorites among the R. fortunei strains. These he had selected because of their fragrance, habit of growth, and size of corolla. To these he tried to add variations in color as well as improvement in form and other characteristics.
During the years from 1921 through 1943 Mr. Dexter both sold and gave away literally thousands of young plants as well as flats of unknown seedlings. These gestures of kindness eventually led to much confusion. As these plants grew and eventually flowered, many were really outstanding. Many more were good but not out of the ordinary. As to be expected in a program of this type, a large percentage of these seedlings proved to be inferior and should have been disposed of when young rather than allowed to grow and eventually be sold as Dexter hybrids.

Mr. Charles O. Dexter.
FIG. 26. Photograph of Mr. Charles
O. Dexter. No information available
as to when it was taken.

Mr. Dexter died from a heart attack on March 10, 1943, at the age of 81 while assisting his plumbers to locate a well on the grounds. A few years after his death a special voluntary and strictly unofficial committee of the American Rhododendron Society members was formed by Dr. Clement G. Bowers and Henry Skinner. It was to locate and evaluate the many Dexter plants growing in gardens along the eastern seaboard. Other horticulturists and rhododendron enthusiasts invited to join in this search included Edmond Amateis, Paul Bosley, David G. Leach, Paul Vossberg, John C. Wister, and Donald Wyman.
For over 10 years this committee worked either as a group or individually  observing as many of these plants as possible, noting and tagging those worthy of future study. Later the owners of these selected plants allowed cuttings to be taken. These in turn were propagated by committee member Paul Vossberg at the Westbury Rose Co., Westbury, Long Island. The initial costs were borne by the Arthur Hoyt Scott Foundation of Swarthmore College, Swarthmore, Pa., where all rooted cuttings were to be first grown.
It was agreed that a complete set should be grown and retained at Swarthmore. As surplus plants became available they would be given to committee members for study and hardiness tests. The first of these surplus plants were sent to the Arnold Arboretum Planting Fields Arboretum, and the U.S. National Arboretum. These plants were to be observed and evaluated growing under the climatic conditions in Boston, Mass., Long Island, N.Y., and Washington, D.C. Eventually the best ones were to be named and distributed to cooperating nurserymen. Many plants were named by this committee, and these cultivars are now being sold by several nurseries along the east coast as well as the Pacific northwest.
There are still, after these many years, several unnamed Dexter Hybrids being grown under the original committee numbers. Some of these have ratings as high or higher than those in the original selection. Hopefully they will be named in the near future while members of this committee are still actively interested in this program started a quarter of a century ago. It was stated earlier in this article that there are still inferior Dexter Hybrids being sold in many garden centers along the highway. It is suggested here that the amateur rhododendron enthusiast be careful purchasing these plants if not in bloom at the time unless they bear a cultivar name.
Dexter Rhododendrons at Present In 1967 the former Dexter Estate was purchased by Mr. Josiah K. Lilly, III for the purpose of creating a museum of early Americana to be dedicated to the memory of his father, Josiah Kirby Lilly, Jr.  This beautiful 75-acre estate on the shores of Shawme Lake is now known as The Heritage Plantation of Sandwich, an educational, non-profit museum.  Heritage Plantation's buildings now house the many collections of early Americana gathered by the present owner as well as those collected by his father. These fine collections so beautifully exhibited in surroundings of much horticultural beauty provide the visitor hours of pleasure.  Great care was practiced during the two years of restoration and construction of Heritage Plantation to preserve the many old original Dexter plants and to return this former show­place to its rightful place among the best of our American gardens.  As this is a report on Dexter rhododendrons, our comments will be confined to that subject. We hope that Quarterly Bulletin readers will visit us if in the vicinity of Cape Cod between May 1st and October 15th. Heritage Plantation is open to the public for a slight admission fee every day during that period. The height of our rhododendron flowering season is usually during the last week of May lasting through the first three weeks of June.
During the fall of 1970 a study was made of the known Dexter cultivars, using the March 15, 1963 report of Dr. John C. Wister titled "Rhododendrons; The Dexter Strain Hybrids" as a guide. Dr. Wister at that time was acting as secretary for the previously mentioned committee. A list of eighty-four cultivars believed to be Dexters was compiled, of which only eighteen were represented in the collection here at Heritage Plantation, the garden of their origin.
In November 1970 we visited several gardens known to be growing some of the plants mentioned in Dr. Wister's report. Our hope was that cuttings might be obtained from a few of these missing plants. The following gardens were visited at the time: Longwood Gardens, Winterthur, U. S. National Arboretum, Swarthmore College, John J. Tyler Arboretum, Morris Arboretum, and the Planting Fields Arboretum. These organizations were most interested and cooperative in this project, and we were able to obtain cuttings from forty-five cultivars not represented in our collection. The interest and encouragement conveyed at these various gardens furnished the incentive to make an attempt to locate the remaining cultivars.
This program would have been considerably delayed without the help of Mr. Roger Coggeshall, President of the Cherry Hill Nurseries, West Newbury, Mass., who agreed to propagate the cuttings we had just received and who also promised to root those we would be seeking in 1971. Roger is much interested in this program even though his nursery is situated in an area where it is impractical to grow Dexters commercially. The rooting percentage of the 1970 cuttings was excellent and the young plants were returned to the Heritage Plantation and planted in our nursery frames late last summer.
With that encouragement our first "Dexter Appeal" (see p. 109, Vol. 25, No. 2, April 1971, A.R.S. Quarterly Bulletin, also p. 65, Vol. 5, No. 2, March 1971 A.A.B.G.A. Bulletin) was compiled and mailed to many rhododendron growers throughout the country. The response was most gratifying. From these replies we learned many things, including the fact that we had over­estimated the number of Dexter cultivars. The list was reduced to seventy-nine as some of those listed were not true Dexters. We were fortunate also in being able to locate sources for seventy-five of the seventy-nine listed. In the opinion of Dr. Wister, (a man that has been most helpful to us), the remaining four might never have been named.
Our search program continued during the spring and fall of 1971. From the information already gained we were able to contact growers of the missing cultivars. Several plants were donated, for which we are indeed grateful. Others were purchased, while still others have been ordered for Spring, 1972, delivery. These young plants are to be grown in our nursery and will be used as stock plants for future propagation. Eventually we aim to create mass plantings of "The Best of Dexters", conspicuously displayed in natural surroundings here where they rightfully belong.

R. 'Dexter's Cream' R. 'Dexter's Horizon'
FIG. 27. Rhododendron 'Dexter's Cream'
(DE #437) a low growing fra-
grant variety. Plant is over 40
years old and still is only 5 feet tall
with an 8 foot spread.
FIG. 28. Rhododendron 'Dexter's Horizon'
(DE #480) a hardy pink variety has
withstood temperatures as low as
15° below zero.
Photo by Heman A. Howard

What does the future hold for Dexter Rhododendrons?

We have no reason to believe that the future of the true Dexter rhododendrons is anything but bright and encouraging. Mr. Dexter's plants have been growing in gardens from southern New England to North Carolina as well as parts of the Pacific northwest. They have proven themselves to rank with the best in the above localities, and a few have also done reasonably well in Ohio and Illinois. Qualities not found in the so-called "Ironlads" make the Dexters a perfect supplement to that group of old-time favorites.
Here at the Heritage Plantation plans are well underway for a future test garden. A woodland area has been selected and during the winter all underbrush was cleared. The large oaks, hickories, and pines were thinned to allow for necessary high shade and filtered sunlight. In this area we hope to plant at least two specimens of each variety as well as some of the better numbered but as yet unnamed Dexters. Here an opportunity will be afforded those interested to see and compare the many cultivars on display, and to form their own opinions.
During this past winter a ten-page "Progress Report" was written, printed and mailed to all who participated in the original appeal. A copy was also sent to each local American Rhododendron Society Chapter. This report contains the names of all known Dexter cultivars, code numbers by whom they were named, and names of those who introduced them. An alphabetical list also indicates where the plants are being grown as well as where they can be purchased. Additional copies of this report are available free of charge as long as they last. Please address your request to the author at Heritage Plantation, Box 566, Sandwich, Mass. 02563.
This coming spring it is our intention to gather all possible flowering information, hardiness data, and any other facts pertaining to the various Dexter cultivars. Information and personal opinions are welcomed from readers and will be filed for future reference and a later progress report.
In conclusion we feel that the "Best of Dexters" will continue to be held in high esteem for years to come. Now that sources are known for the various cultivars, nurserymen might be encouraged to make a few of these available to their customers. It is also hoped that this article might stimulate more interest among rhododendron enthusiasts and that they too will request their favorites from their nurseryman.