Hazel’s natural range includes northwestern Asia and Europe, from the Mediterranean north to central Scandinavia and the coast of Finland. In Finland it grows in nutrient-rich deciduous and mixed forest. It prefers slopes and the foot of cliffs, and thrives in the protection of forest groves.
At Mustila, the hazel shrubs on the warm slopes opening to the southeast are of Finnish provenance, planted in or before 1910, probably with an eye to the edible nuts. The tall conifers towering above them provide a suitable degree of shade for the Hazelnut slope. The outward curving stems of the large shrubs offer luxuriant arches, bright green in spring, deep green in summer, and a beautiful yellow in autumn. The mature leaves provide deep shade for the forest floor, and when they fall they are gradually converted into rich soil, feeding the under-storey shrubs and perennials.
Early in spring the hazel shrubs carry decorative catkins. After pollination the female flowers gradually develop into nuts, enclosed in a protective husk. When the husk opens in autumn the nuts are ripe for picking. This picking season is an important job at the Arboretum in August-September. The local squirrels join in enthusiastically.