The Rhododendron Collection – laurelwoodarboretum.org

Dorothy Knippenberg began hybridizing rhododendrons in 1955 at Laurelwood Gardens, and she continued to strive for plants with new interests and improvements, such as hardy large-leaf plants, more flower substance, and later-blooming periods. In anticipation of donating the 30-acre site to Wayne Township for a public rhododendron park, the Knippenbergs began assembling masses of the hardiest varieties of rhododendrons.

Today, the arboretum reflects their efforts and is a showcase of one of the largest public rhododendron collections in New Jersey, with more than 450 rhododendron hybrids and species, including more than 100 different named rhododendron hybrids. Many of the rhododendrons are more than fifty years old and include rhododendrons hybridized and propagated by the Knippenbergs over the years, imported from nurseries in England and the Netherlands, and purchased from local and West Coast nurseries.

The Rhododendron Tree

One of our oldest hybrid rhododendrons is probably ‘Babylon’, located near the top of Long Valley Road. With its large, openly funnel-shaped flowers – 4” to 5” across – and a deep red blotch in its throat, there is probably no better example of a “Rhododendron Tree” in Laurelwood. Hybridized in 1955 by G. Reuthe, Ltd. in Kent, England, it was imported by the Knippenbergs as part of their efforts to assemble masses of the hardiest varieties of rhododendrons. Standing more than 15 feet tall, it is one of the tallest rhododendrons in the arboretum. It blooms between mid-April and the first week of May, depending on weather conditions.

Ridge Road

Located on Ridge Road at the intersection with Long Valley Road, the Dexter Garden includes a grove of massive, large-leaf rhododendrons hybridized by Charles O. Dexter of Sandwich, Massachusetts. His hybrids are characterized by dense foliage, large stature, and flowers of superior size and color. The garden includes many of his mature hybrids, including ‘Dorothy Russell,’ ‘Dexter’s Pink Satin,’ ‘Parker’s Pink,’ ‘Westbury’, and ‘Dexter’s Harlequin.’ His hybrid, ‘Powder Puff,’ located on Long Valley Road, was named by Dorothy Knippenberg in 1978. Overall, there are more than 60 Dexter hybrids growing in the arboretum.

Other unique plants found along Ridge Road were hybridized by early pioneers Guy Nearing and David Gable, and others, including the rhododendron ‘Paul Vossberg’, which was grown at Laurelwood Gardens and named by Dorothy Knippenberg circa 1975.

Brook Road

Along Brook Road, visitors can observe many mature rhododendrons planted many years ago along the hillside and new additions propagated by our rhododendron propagation team as well as donations from private gardens. Visitors are encouraged to view the rhododendrons from Brook Road, including ‘Westbury,’ ‘Lavender Princess’ and ‘Wheatley’ or to walk along secluded Dorothy’s Way amid the stately specimens on the hillside, including Dorothy Knippenberg’s award-winning ‘Carolina Rose.’ The path takes you up close and very personal under and among the huge rhododendrons.

One of only a few yellow rhododendrons in the arboretum, ‘Sea Gold’ can be seen along Brook Road with its pink buds opening to a medium golden yellow. Hybridized by Allan and Shirley Anderson of Franklin Lakes, it was donated to the arboretum along with several of their other hybrids that can be seen nearby, including ‘Amanda Joan Young’ and ‘Kelsey Lynn Young’, which were registered and named for their grandchildren.

Our rhododendron collection is the legacy left behind by a person with vision. A mass of rhododendrons growing in a natural setting. They help to tell the story of Laurelwood and have become an important resource for gardening enthusiasts and the public at large.

Most of the rhododendrons are typically in bloom in mid-May, depending on weather conditions. New rhododendrons are added to the collection each year from commercial nurseries and the arboretum’s rhododendron propagation program

Registration of Rhododendron Names

Registration of names for cultivars in the genus Rhododendron is managed by the Royal Horticultural Society in its role as the International Cultivar Registration Authority for the genus. John and Dorothy Knippemberg had eight rhododendron cultivars registered with the American Rhododendron Society and the Royal Horticultural Society. Dorothy Knippenberg is credited with naming the rhododendrons ’Powder Puff,’ ‘Paul Vossberg,’ ‘Dexter’s Pink Satin,’ ‘Great Eastern,’ ‘Carolina Rose,’ and others.