Fruit Trees – The Walnut – Juglans regia, J nigra

Trees & ShrubsFruit Trees – The Walnut – Juglans / Juglans regia – J. nigra

Walnut trees are any species of tree in the plant genus Juglans, the type genus of the family Juglandaceae, the seeds of which are referred to as walnuts. All species are deciduous trees, 10–40 metres (33–131 ft) tall, with pinnate leaves 200–900 millimetres (7.9–35.4 in), with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts (Pterocarya), but not the hickories (Carya) in the same family.

The common name walnut derives from Old English wealhhnutu, literally ‘foreign nut’ (from wealh ‘foreign’ + hnutu ‘nut’), because it was introduced from Gaul and Italy.

The two most commercially important species are J. regia for timber and nuts, and J. nigra for timber. Both species have similar cultivation requirements and are widely grown in temperate zones.

Walnuts are light-demanding species that benefit from protection from wind. Walnuts are also very hardy against drought.

When grown for nuts, care must be taken to select cultivars that are compatible for pollination purposes; although some cultivars are marketed as “self fertile”, they will generally fruit better with a different pollination partner. Many different cultivars are available for growers, and offer different growth habits, flowering and leafing, kernel flavours and shell thicknesses. A key trait for more northerly latitudes of North America and Europe is phenology, with ‘late flushing’ being particularly important to avoid frost damage in spring. Some cultivars have been developed for novel ‘hedge’ production systems developed in Europe and would not suit more traditional orchard systems.

Walnuts are very attractive trees in parks and large gardens. Walnut trees are easily propagated from the nuts. Seedlings grow rapidly on good soils. The Japanese walnut in particular is known for its huge leaves, which have a tropical appearance.

As garden trees, they have some drawbacks, in particular the falling nuts, and the releasing of the allelopathic compound juglone, though a number of gardeners do grow them. However, different walnut species vary in the amount of juglone they release from the roots and fallen leaves – J. nigra, in particular, is known for its toxicity, both to plants and horses. Juglone is toxic to plants such as tomato, apple, and birch, and may cause stunting and death of nearby vegetation. Juglone appears to be one of the walnut’s primary defence mechanisms against potential competitors for resources (water, nutrients and sunlight), and its effects are felt most strongly inside the tree’s “drip line” (the circle around the tree marked by the horizontal distance of its outermost branches). However, even plants at a seemingly great distance outside the drip line can be affected, and juglone can linger in the soil for several years even after a walnut is removed as its roots slowly decompose and release juglone into the soil.

Edward Step the horticulturalist had this to say about the The Walnut (Juglans regia).

The Walnut (Juglans regia).

Walnut-Juglans-regia-fruit Fruit Trees - The Walnut - Juglans regia, J nigra
Walnut – Juglans regia fruit

In the Golden Age, when man lived happily on a handful of acorns, the gods fed upon walnuts, and so their name was Jovis glans—the nuts of Jupiter—since contracted into Juglans. Those who delight in obvious interpretations by appealing to the modern meanings of words similar in construction may be pardoned for supposing that Walnut-trees were formerly trained against walls; but, like many other obvious interpretations, this is wide of the mark. Some have gone back to the Anglo-Saxons for help, and though the result arrived at is in all probability the correct one, it is almost certain that the Anglo-Saxons knew nothing of the matter, and would scarcely trouble to give a name to something they had never seen. The Walnut is a native of the Himalayas, the Hindu Kuh, Persia, Lebanon, and Asia Minor to Greece. The learned Roman, Varro, who was born B.C. 116, and died B.C. 28, mentions it as existing in Italy in his day; and Pliny tells us it was brought thence from Persia. The date of its introduction to Britain is usually set down as about the middle of the sixteenth century, but it was probably at least a century earlier, for Gerarde, writing at the close of the sixteenth century, describes it as a tree commonly to be seen in orchards, and in fields near the highways, where a very new importation was not likely to be found. But to return to the name: there can be little doubt that it is a contraction of Wälsh-nut (in modern spelling, Welsh-nut), meaning foreign. This is German, and while the modern sons of the Vaterland write it Wallnuss (occasionally Wälshenuss), the Dutch form is Wallnoot. That this is the true derivation is made pretty certain by Gerarde, who calls it “Walnut, and of some Walsh-nut.”

A-female-flowers-B-male-flowers Fruit Trees - The Walnut - Juglans regia, J nigra
A, female flowers; B, male flowers

That the new importation was fully appreciated in Europe for its fruit may be judged by the extent to which its cultivation had spread in Evelyn’s day, for he tells us the trees abounded in Burgundy, where they stood in the midst of goodly wheat-lands. He says: “In several places betwixt Hanau and Frankfort in Germany no young farmer is permitted to marry a wife till he bring proof that he hath planted and is a father of such a stated number of [Walnut] trees, and the law is inviolably observed to this day, for the extraordinary benefit the tree affords the inhabitants.”

The Walnut is a handsome tree, growing to a height of forty to sixty feet, with a bole twenty feet or more in circumference, and a huge spreading head. The bark is of a cool grey colour, smooth when young, but as the tree matures deep longitudinal furrows form, and it becomes very rugged. The twisted branches take a direction more upward than horizontal, but in early summer they are almost completely hidden by the masses of large and handsome leaves of warm green colour and spicy aroma. I once rejoiced in the occupation of a garden that held two Walnut-trees, and though they had not attained to the fruiting age, their possession was a delight to me; but then I am one of those who enjoy their fragrance, which is unbearable to some persons. The large leaves are formed after the fashion of the Ash-leaf—broken up into a variable number of lance-shaped leaflets with scarcely perceptible teeth.

Walnut-Juglans-regia Fruit Trees - The Walnut - Juglans regia, J nigra
Walnut – Juglans regia – in winter

The flowering of the Walnut is much on the plan of the Oak and the Hazel, the sexes being in different flowers, but borne by one tree; the males forming a long drooping catkin of slender cylindrical form, the females being solitary, or a few grouped at the end of a shoot. Separated from the catkin, the males will each be seen to consist of a calyx of five greenish scales, enclosing a large number of stamens. The calyx of the female closely invests the ovary, which has two or three fleshy stigmas. The flowering takes place in early spring, before the leaf-buds have burst. The fruit is a plum-like drupe, only the enveloping green flesh becomes brown, and, splitting irregularly, discloses the “stone,” which in this species takes the form of a hard but thin-shelled nut—the well-known Walnut, with its wrinkled kernel of crisp white flesh, from which a fine oil is obtained. The ripening of these nuts—which is accomplished by the beginning of October—can only be relied upon in the southern half of Britain, and even there the crop is often spoiled by late frosts in spring. Its chief value in Europe is as a fruit-tree, though the light but tough wood is much esteemed for the manufacture of furniture. Owing to its rapid growth, the grain is coarse, but the dark-brown colour is esteemed, especially as it is relieved by streaks and veins of lighter tints and black. It is easily worked, and bears a high polish. The wood of young trees is white, gradually deepening to brown as maturity is approached. All the juices of the tree, whether from wood, bark, leaves, or green fruit, are rich in the brown pigment to which the hue of the timber is due. The combined lightness and toughness of the wood led to its adoption as the favourite material for making the stocks of guns and rifles. It is said that so great was the demand for this purpose during the Peninsular War, that a single Walnut-tree realized £600 for its timber, and this created a boom that led to the cutting down of all our finest Walnut-trees. Some of these were doubtless the very trees referred to by Evelyn, who tells us the Walnut was extensively planted at Leatherhead in Surrey, also at Cassaulton (Carshalton) and Godstone in the same county, where the rambler may come across fine Walnut-trees to this day, and occasionally to young ones growing wild in hedgerows and wastes.

walnut-summer Fruit Trees - The Walnut - Juglans regia, J nigra
Walnut – Juglans regia – in summer

The old doggerel adage,

“A dog and a wife and a walnut-tree, the more they are beaten the better they be,”

has reference to the manner of harvesting the ripe fruit. Evelyn says: “In Italy they arm the tops of long poles with nails and iron for the purpose [of loosening the fruit], and believe the beating improves the tree; which I no more believe than I do that discipline would reform a shrew.” He expresses no opinion on the question of beating dogs.