The University Gardens
The Collections


The arboretum takes special pride in its rhododendrons, including cultivar and species collections

Nydalen 2017
Bjørn Moe

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From the very beginning in 1971, the arboretum has taken a special pride in its Rhododendrons. We have built up two main collections: a cultivar collection and a species collection. The cultivar collection is located in Nydalen and includes 2,300 specimens of 600 different species, while the species collection, located north of Mørkevatnet, includes 1,700 specimens of almost 300 species.

The cultivar collections are arranged in themed groupings that describe the sequence of introductions of species and their hybrids into cultivation. We aim to show the diversity that is available and present the best cultivars from different eras and from different countries: everything from the latest novelties, to the oldest English and German varieties. The species collections are arranged systematically, following the Edinburgh classification.

Rhododendron belongs to the heather family. It is the largest woody plant genus on the planet, with over 1,000 different wild species, from creeping dwarf shrubs to huge trees 30 meters high. The flowers can range from small thimbles to heavy, lily-like beauties of 15-20 cm long, some of which are fragrant. The colours often vary between white, pink and violet, but some species are bright red, yellow, or orange.

The main flowering is in May, but in mild winters the first flowers come as early as January, and some rhododendrons can bloom as late as September or October. Most of them are evergreen, but there are also deciduous rhododendrons (azaleas), which provide autumnal colour.

Like most of their ericaceous relatives, rhododendrons like acid soil. They thrive best in humid climates where it is mild in winter, as in their natural habitats. Most come from humid areas of the Himalayas, but a few are found growing in Europe and North America. There is a large group found in the tropical islands of Southeast Asia, but these cannot be grown outside at our latitude.