The Arboretum was founded in 1806, when the plot next to the Emajõgi river received its first woody plants from various phytogeographic zones of the world. Over two centuries and more, the Arboretum has gone through several changes – historical sections have been reorganised and new exciting species of shrubs and trees planted.
The Arboretum covers most of the Garden's grounds and falls into three geographical sections: East Asia, Europe, and North America, with corresponding herbaceous vegetation covering the grounds surrounding the trees.
A large part of the Arboretum is made up by the East Asia section, which is historically located in the triangular area behind the principal greenhouse. The section has gradually expanded to the slope facing the pond, where rhododendrons attract the visitor's eye.
The oldest part of the East Asia Garden is notable for several species of maple as well as for large walnut and cork trees. The Manchurian cherry (Prunus maackit) with its beautiful fissured bark has been named after Richard Maack, a researcher of East Asian flora who was born in Estonia.
The Garden also cultivates several lianas typical of East Asia – the Garden's pavilion is covered by Dutchman's pipe (Aristolochia macrophylla) while Manchurian pipevine (Aristolochia manshuriensis) climbs high on the trunk of the great larch. The slopes beneath the trees provide a favourable environment for hostas (Hosta) and barrenwort (Epimedium).
With the arrival of the first frosts, the East Asia garden turns a fiery reddish yellow – one of the most beautiful autumn sights in the Botanical Garden!
The section of woody plants of North American origin is located in the north-western part of the Botanical Garden and on the slope of Bastion Hill. When taking a walk along path that passes behind the hill, the visitor's eye is first drawn to white firs (Abies concolor), an eastern redbud (Cercis canadensis) and mountain witch alders (Fothergilla major).
The Garden also has three of North America's four species of tsuga and, in close proximity to these, the most widespread conifer of the zone, the white spruce. Higher up on the slope is one of the tallest grand firs (Abies grands) in Estonia and, on the lawn in front, several species of North American deciduous trees. The sheltered area under the trees provides a favourable environment for various species of trillium and ferns.
A children's playground and a picnic area are also situated in this part of the grounds.
Already during the Garden's initial years, the steep slopes of Bastion Hill were envisaged as a tree garden. The north slope has traditionally been used for cultivating trees and shrubs of European origin – in recent years, also for cryptogams.
Since very few modifications have been made on tree garden grounds during the second half of the 20th century, the older part of the garden has relatively few species. The upper level of the garden – local species of maple, oak, elm and lime – provide shade to mosses and a perch for singing birds. Next to the bust of Gottfried Albert Germann a typical representative of Central European broad-leaved forests – the common beech (Fagus sylvatica), which was also present in Estonian territory 6500-5000 years ago – stretches its branches wide.
Although coniferous trees can be found also in other sections of the Garden, it was only in the 1970s that preparations were made to create a conifer section. Small groups of conifers occupy the strip of ground along the wall on the north side of the Garden. Now there are close to 70 species and varieties of conifers. The selection is based on a preference for different varieties, including experiments with new frost-sensitive trees and shrubs. Time will show which of these can survive in our fickle climes. Conifers are remarkable plants in that they continue to grace a garden with shape and colour also when it is covered by a thick carpet of snow.
The pride of the Garden can be seen to the left of the main gate where a great larch (Larix sp) rises to 25 metres, boasting a trunk circumference of 3.65 metres and an age (according to a dendrochronological study that estimated it to be 270 years) that trumps that of the Garden.