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100 Years of Rhododendrons

Within the gardens is an impressive collection of rhododendrons, which were hybridized by the internationally-known Charles Owen Dexter. Each spring when the rhododendrons bloom at Heritage, new Dexter cultivars are evaluated annually and some are named.

  • Heritage has approximately 160 named varieties of Dexter and Cowles rhododendrons and thousands of unnamed varieties
  • Dexter rhododendrons can be found in colors ranging from pure white, to pale yellow and pink to red and purple with combinations of each.
  • Typical bloom season: early May to mid-June

Read more about Dexter and the rhododendrons at Heritage Museums & Gardens below, or visit our About Rhododendrons page for more information on growing and caring for rhododendrons.

Rhododendron Pruning
More about Rhododendrons

Charles Owen Dexter and Rhododendrons

History of Dexter & Rhododendrons

With his uncle and cousin, established the Beacon Manufacturing Company, which became one of the largest manufacturers of cotton blankets in the United States.

Dexter bought the Heritage property, then known as Shawme Farm, in 1921 and began spending summers with his wife at Shawme Farm. Worked with Paul Frost, a well-known landscape architect from Cambridge, to turn the wooded Shawme Farm into a country estate and to assist in his hybridizing working. Started hybridizing rhododendrons in 1921 and worked for the next 22 years (1921-1943) on these plants in his garden. He started with vegetables and expanding his interest to rhododendrons. Dexter was friends with Charles S. Sargent, then Director of the Arnold Arboretum of Harvard University, as well as Ernest Wilson, the famous plant collector (also of Arnold Arboretum). Many of the trees and shrubs on the property are most likely plants from these two gentlemen and from the landscape architect Paul Frost.

To develop his rhododendrons, Dexter collected plants from around the world, attempting to take the best characteristics from each plant and combine them into new cultivars. Records indicated he used in his crosses:

  • Rhododendron decorum
  • fortunei (dominant species in his work)
  • griersonianum
  • haematodes

Dexter’s Breeding Goals

Dexter’s breeding goals were hardiness, clear bright colors, fragrance and big blossoms. His plants are typically hardy to -10 but flower buds are hardy to about 5 degrees above. At the height of his hybridizing, Dexter created over 10,000 rhododendron seedlings a year.

In the years 1945-1953, a rhododendron study group led by John Wister, then Director of the Scott Horticultural Foundation of Swarthmore College, Swarthmore, PA, began the search for plants that had left the former Dexter Estate. Over those years this group studied and collected plants from Longwood Gardens, the U.S. National Arboretum, Winterthur, John J. Tyler Arboretum, Morris Arboretum and Planting Fields Arboretum, as well as several other estates and gardens. The plants were propagated and eventually (1970-1972) brought to Heritage Museums & Gardens where they were evaluated and a selection of Dexter’s cultivars were named.

Heritage’s most notable rhododendrons include: 

  • ‘Scintillation’- with a subtle pink color with shades of yellow, ‘Scintillation’ is considered to be the best of the plants created by Dexter. It can grow up to 8’ tall and 8’ wide in 20 years, has a pleasant fragrance, and when closely examined, it’s flower clusters are 8-10” across and made up of 20+ funnel-shaped clear pink blossoms with freckling on the upper side.
  • ‘Yellow Gate’- hybridized by Dexter Estate Superintendent J.C. Cowles in the 1960s, the ‘Yellow Gate’ rhododendron begins its bloom with coral pink buds that open into vibrant yellow petals.
  • ‘Dexter’s Orange’ – an original Dexter hybrid that boasts wonderful pink flowers that appear orange from a distance. They have the added bonus of being wonderfully fragrant.
  • ‘Dexter’s Spice’ – boasts one of the largest white flower clusters of any rhododendron. This cultivar is known for its fragrant flowers that has a distinctive spicy fragrance.
  • ‘Eben Jordan’- hybridized by Dexter Estate Superintendent J.C. Cowles in the 1960s, Eben Jordan is known for its beautiful magenta color with a white blush and deep magenta spots.

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