Juglans

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.

Manchurian walnut is a large, broad and often multi-stemmed tree, growing bestg in moist rich soils. The leaves are alternate, compound, a dull bluish-green, and on strongly growing root-collar shoots can be over a metre long. Because of their size they make an indelible impression on visitors to Mustila’s Etelärinne (Southern slope).

Manchurian walnut, the winter-hardiest of the genus due to its origins in cold continental climate areas, has been planted in Finland for a century, though still rare. At Mustila there are large trees which have been grown from Manchurian walnut seed purchased from the Russian seed merchant Ptitšin in the 1930s.

The nut is large, thick-shelled, and ripens in October. The nuts are edible, like the English (synonym Persian) walnut (Juglans regia), but much more difficult to crack open. Despite this, squirrels enjoy them and the grinding of their teeth on the shells can be heard in the trees in autumn.

Butternut grows naturally in the north-eastern United States and also – though rarely - in southern Canada. It is a large multi-stemmed tree with grey bark and a broad crown. The decorative oddpinnate leaves are 25-50 cms (10-20 inches) long, with 11-19 leaflets in opposite pairs. The flowers are unpretentious, but the fruit is a hard-shelled nut 6-8 cms long inside a sticky fleshy covering, ripening in September. The shell is sharp-ribbed into sections and needs to be handled carefully to avoid lacerations.

In America suitable plants have been selected to produce new forms and subspecies whose shells break more easily and contain bigger tasty nuts. The species is also used worldwide in landscaping.

At Mustila, the walnuts are among the most eye-catching of the broadleaf species because of their foliage. The butternut is among the first species to have been planted on Etelärinne (Southern slope). It takes on autumn colour, a beautiful yellow, later than the Manchurian walnut, which is the hardiest of the genus.