Rhododendron Dell is a contemplative landscape showcasing the Arboretum’s core collection of hybrid and evergreen rhododendrons. An overstory of hemlock, birch, oak, maple, and pine provide ideal rhododendron habitat. In the early 1900s, Ernest Henry Wilson evaluated many of the rhododendrons in the collection and in 1917 published a list of “ironclads”—a group of hybrid rhododendrons that had proved hardy and floriferous at the Arnold Arboretum. Bred in the United Kingdom, these ironclads became the focus of regional plant introduction and breeding endeavors in New England. Many of the original ironclads, acquired in 1886 from the Woking Nursery in England, are the largest plants in the collection.
Today, rhododendron collections in Rhododendron Dell include 175 plants representing 88 taxa (kinds). Of these, 66 are cultivars which have been selected for horticultural merits including flower color and fragrance, truss (domed flower mass) size, leaf morphology, and hardiness.
Extensive renovations in Rhododendron Dell were accomplished in 1990 with funds received from the Linda J. Davison Memorial Trust. Notable features include: a path through the collection, a bridge spanning Bussey Brook, engraved stone destination signs, and a hen’s tooth puddingstone wall designed by landscape designer Julie Moir Messervy. Bank erosion along Bussey Brook was also temporarily mitigated by adding stone and logs to the channel. Over subsequent years, and to the present day, new rhododendrons have been added to the collection for research and ornamental display. The most recent additions to the collection include wild sourced Rhododendron maximum (rosebay rhododendron) and R. catawbiense (Catawba rosebay), both native to North America.
- Native to China, Rhododendron fortunei was introduced to the west by British plant explorer Robert Fortune. This species and its multitude of crosses have large, heady-fragranced flowers in a range of colors. While most rhododendrons have five petals, this species typically has seven.
- R. ‘Duke of York’ (a cross of R. fortunei) is one of the tallest rhododendrons in the collection and typically flowers in profusion over several weeks beginning in mid May. This triple leadered specimen is 20 feet tall with an equal spread.
- Native to North America, Catawba rosebay (R. catawbiense) have purple to lavender-pink colored flowers with yellow-brown blotch. The epithet catawbiense is derived from the Catawba River of North Carolina and South Carolina. Following the description of the species by French botanist André Michaux, plant breeders began crossing R. catawbiense with other rhododendrons. Today, hundreds of sun-loving, cold hardy cultivars available in nurseries have R. catawbiense in their parentage. The Arboretum’s ironclad rhododendron are examples.
- R. ‘Blue Peter’ (a cross of R. ponticum) flowers are held in a tight dome (truss) and are lavender-blue with a dark purple blotch. At the Arboretum, its habit is shrubby with flowers borne on erect stems.
The Arboretum’s core collection of hybrid and broadleaf evergreen rhododendron are located just inside the South Street Gate along Valley Road. The collection lies about a forty minute walk from the Arborway Gate, and about ten minutes from the Bussey Street Gate and the Centre Street Gate. If driving, park at the South Street Gate.
The Linda J. Davison Rhododendron Path is bark mulched. In a few places, large stepping stones aid circulation. A bridge across Bussey Brook provides access to additional uneven paths leading to Rhododendron collections on the northeastern slopes of Hemlock Hill.
An information kiosk at the Bussey Street Gate provides seasonal updates. Map tables at the South Street Gate and the southern end of Beech Path provide Arboretum wayfinding information.
New! Link to a tour of this collection on Arboretum Explorer. Our new web application allows you to take self-guided tours of featured plants in our landscape. Follow this link and you will see colored leaf icons. Click/tap on an icon to get a plant name and image; click/tap the circled “i” on the right to get more detailed information. For more information on how to use the mobile application click/tap on “Help” in the menu.
How long should I explore?
Plan to spend about fifteen minutes exploring the Rhododendron collection in Rhododendron Dell, and longer when the plants are in bloom between May and early June.
Plan your visit to the Arboretum.
- Port, K. 2013. Rediscovering Rhododendron Dell, Part 2. Arnoldia 71(1): 15-25. [pdf]
- Port, K. 2013. Rediscovering Rhododendron Dell, Part 1. Arnoldia 70(4): 15-18. [pdf]
- Madsen, K. 2000. In pursuit of ironclads. Arnoldia 60(1): 30-32. [pdf]
- Wyman, D. 1969. Seventy-five years of growing rhododendrons in the Arnold Arboretum. Arnoldia 29(6): 33-40. [pdf]
- Sargent, C. S. 1914. [Rhododendrons.] Bulletin of Popular Information no. 57, June 5, 1914. [pdf]
- Nilsen, E. T. 1990. Why do rhododendron leaves curl? Arnoldia 50(1): 30-35. [pdf]
- Brooks, R. 2000. A Fresh Look at a Traditional Favorite: Rhododendrons. Arnoldia 60(1): 20-26. [pdf]
Culture and Care
- Fillmore, R.H. 1949. Growing Rhododendrons from Seeds. Bulletin of Popular Information no. 9, November 4, 1949. [pdf]
- Wyman, D. 1948. Pruning rhododendrons. Arnoldia 8(8): 37-44. [pdf]
Search for related articles in Arnoldia, the magazine of the Arnold Arboretum.
- Azalea Border, Arnold Arboretum
- Massachusetts Chapter of the American Rhododendron Society
- American Rhododendron Society
- Azalea Society of America
- Rhododendron Gallery, Rhododendron Species Botanical Garden