The arboretum is started to create in 1960. It is the greatest part of the exposition area (45 ha) and includes 2 parts: the oldest one (20 ha), where trees and ashrubs are planted according to phylogenetic system and the new one (25 ha), where the plantings are made according to geographical principle. In the arboretum, including nurseries and fund plantations are about 4500 taxa of trees, shrubs and climbers. Scientifically the most nothewort part of this collection are plants, grown from the seeds collected in the wild in the botanist's expeditions.

In the conifer collection are

1138 taxa, including about 600 low ornamental cultivars and forms, that is one of the world's biggest collections of such kind.

Collections of deciduous trees and shrubs. Crataegus collection is of world's walue and contains about 200 taxa (from the world's known 400), there are mostly North American, but also a lot of Far East species. Many species have medicinal value, some have edible fruits. Some ornamental cultivars have beautyful double flowers. The thorns of Crataegus macracantha are to 14 cm long. C.arnoldiana and C.punctatus have delicious fruits.

Krustābeles šķirne (Crataegus laevigatus 'Punicea')

Bright and diverse are also collections of apple trees species and ornamental cultivars (Malus - 100), so as other collections, more of them are of national value: Cotoneaster - 80; Spiraea - 70, Betula - 100, Sorbus – 130, Berberis – 150, Salix – 250, Populus – 160, Rosa species – 100, Ericaceae - 300 (incl. 150 Erica, Calluna a.o. small shrub species ans cultivars).