The northernmost naturally growing black walnuts are to be found in the areas south of America’s Great Lakes. This species is the longest-lived and biggest-growing of all the walnuts. It can live for several hundred years and achieve heights of 50m (165 ft.) in suitable places. It has a long straight trunk which it maintains into old age.
Black walnut’s leaves are glossy, smaller and more numerous than those of most of its relatives. The fruit has a thick rough shell protecting the almost spherical edible nut. In its native habitat it produces both nuts and valuable, beautiful timber. Trees producing thinner-shelled nuts have been selected for commercial production.
Very few mature black walnut trees are to be found in Finland. Since 1993, Mustila has procured seeds from the northernmost plantings in its native area, and seedlings from these provenances have proved exceptionally winter hardy. The young trees have already achieved a degree of showiness, for example in the Arboretum yard and by the road along the bottom of Pohjoisrinne (Northern slope) near the nursery.