Walnut tree: Why species may be world's most underappreciated

THE botanical name for the walnut tree genus is Juglans, which roughly translates to ‘Jupiter’s nut’. It belongs to the Juglandaceae family, a group that includes the hickories and pecans (Carya spp.).

The word Juglans is thought to derive from the Latin Jovis glans, meaning ‘Jupiter’s acorn’. The Romans associated certain species of trees with their gods and, in this case, the mighty walnut tree was linked to Jupiter, the king of the gods, as the fruit was said to be reminiscent of his external male reproductive anatomy.

Walnuts (of different species) are native to eastern Asia, southern Europe and North and South America. The 21 species in the genus range across the north temperate old world from southeast Europe towards the rising sun of Japan, and more widely in the new world from southeast Canada westwards to California and south to Argentina.

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Central Asia is the cradle of many classes of hard fruit we now take for granted across our blue planet. Of these, the nuts of J. regia have been unearthed in Iron Age archaeological sites in Europe. The ancient Greeks, Romans and Persians cultivated walnuts as food. Persian varietals were considered superior in taste, size and oil content. 

The Persian walnut made its way to China by 400 AD, and was imported to England in the 15th century, although cultivation of the nut never really took off in these islands. However, English merchants helped spread this nut across much of the rest of the world though, so the name ‘English’ walnut stuck.

IN THE UK

The walnuts are, of course, dual-purpose trees, famed for both their timber and their nuts. 

J. regians was one of the ancient arboreal introductions to Britain, probably as early as the 15th or 16th centuries, if not by the Romans. Yet there are probably fewer walnut trees still alive here nowadays than several centuries ago. That is likely due, in part, to mahogany timber from the then-thriving former colonies of the British Empire being imported and ousting home-grown walnut in more elegant furniture and in price. Beech, too, was planted as a cheaper alternative in places such as the Chilterns.

Fruit of a common walnut tree (Juglans regia) growing in a country cottage garden in Devon. (Image: Peter Turner)

A sprinkling of watering holes across the land still sport ‘walnut’ in their titles – mainly in the south, but with outliers as far north as Yorkshire and Lancashire. 
Most UK tree boffs and foresters are well aware that common or English walnut is site-demanding, often of poor form and is particularly prone to damage from late spring frosts.

The so-called English walnut is an attractive dual-purpose species to grow for landowners for nuts and timber.

When cultivated on the right site, it can produce a final nut crop on a 50-year rotation, and the timber can be more valuable than veneer oak. But growing it is finickity and it is a challenge to encourage it to grow straight if timber is one end goal. 

This tree does best on rich, fertile soils, most of which are already given over to faster growing and more lucrative cash-quick annual crops such as cereals in the UK. 

The last few years have seen a latent or incipient resurgence of interest in growing J. regia for nuts and timber in the UK, where climate change may aid growing conditions. Some provenance trials have been undertaken in recent years in Oxfordshire and the National Forest in the Midlands. 

Walnuts will grow and produce nuts in the UK in a good summer – provided grey squirrels don’t get there first.

One rare and picturesque experimental example of an early 20th-century walnut orchard was being helped to mature gracefully thanks to government funding at Orchard Farm, near Boxted on the Suffolk/Essex border. That first grew out of a 1927 project to rejuvenate English walnut growing; it is believed to be the only surviving sizeable site but has now been sold and faces an uncertain future. 

NUTS

Technically speaking, the walnut fruit is not a nut, but a drupe — a stone fruit in which an outer fleshy skin surrounds a hardened shell, protecting a seed inside.
The three species of walnuts most commonly cultivated for their edible seeds are the Persian (or English) walnut (J. regia), originating from Iran, the black walnut (J. nigra) – native to eastern North America – and the Japanese walnut or heartnut (J. ailantifolia).

When conditions are not ideal for walnuts to ripen fully, they can be harvested green or ‘wet’ in late summer and pickled. Food historians tell us how these were very popular in the 1700s and were usually consumed on Boxing Day alongside leftover cold meats, presumably because of their ability to enhance the flavour of meat dishes.

Such ‘green’ walnuts can still be found on sale here if you know where to look. 
Mature dried English walnuts are often marketed as a wonder food. Like most nuts, they are high in protein and fibre. They’re also loaded with nutrients, like vitamin B6, and trace elements. They are a great source of both omega-3 and -6 fatty acids, essentials for the body to build brain and nerve cells. They also may lower the risk of heart disease. 

Bark of the walnut tree. (Image: Getty Images/iStockphoto)

As a group, walnuts boast a wide variety of medicinal qualities. The leaf is used in the treatment of conditions, including swelling of the skin, acne, ulcers, diarrhoea and excess sweating. The nuts are said to help lower cholesterol, while the shell is used in the treatment of blood poisoning. The leaf is employed in tanning agents and hair dyes.

Across the Atlantic, black walnuts have been used since time immemorial as a traditional medicine by developing nations to treat ailments ranging from parasites to constipation.

Early New England settlers later introduced the Persian or English walnut to North America, where it gained prominence over the harder-to-hull or shuck and more bitter black cousin. 

Edible walnuts, which are consumed worldwide, are usually harvested from cultivated varieties of the species Juglans regia. China produces over half of the world total of roughly 4 million tonnes. Other major producers are the USA and Iran.

Some species of walnut show the phenomena alleopathy. Naturally produced chemicals wash off their leaves and inhibit the germination and growth of other plants under their drip lines. Such compounds may be scented and serve as insecticides or repellents. 

English walnuts may have been planted alongside ancient carting routes in these isles to ward off flies and provide shade in laybys for cart horses taking a break but only the odd veteran specimen tree persists.

IN CALIFORNIA

I have witnessed harvesting walnuts in California firsthand. It is a sight to behold and takes gathering this crop to a whole new level.

According to the California Walnut Board, Franciscan monks were the first to cultivate these nuts in the sunshine state in the 1700s, although the first commercial plantings of the nut there weren’t until 1867.

Depending on the variety, this high-tech activity begins in late August, when the first drying green hulls on the crop start to split (allowing the walnuts to be removed) and continues until late November. 

First, the orchard floor is swept clean by machines akin to road sweepers and leaf blowers. Then, mechanical shakers clasp the trunks and shake the trees to within an inch of their lives. Cruelty to trees if ever there was. Thousands of walnuts rain down to earth where they are hoovered up for drying, de-shucking and processing. 

A large common walnut tree with a few flowers left in Exeter. (Image: Getty Images/iStockphoto)

So spare a thought for the life of the walnut and how they reached your table this coming festive season whilst searching for the nutcrackers which were put away ‘somewhere safe’ this time last year to resurface.

In addition, burrs from old trees in orchards past their best as nut bearers can command eye-watering prices.

TIMBER 

There are six named classes of walnut timbers – English, black, Claro, white, Bastogne, and Peruvian walnut. Although walnut is popular with woodworkers, some types are not quite strong enough to fashion into furniture. Some examples of this are the Peruvian and white walnut.

The fine, straight-grained lumber from the black walnut from North America is highly valued for furniture, wall panelling, automobile interiors, and gunstocks.
Walnut wood is very stable and relatively easy to work. It is strong without being too heavy and can withstand considerable shock which may have made it popular as gunstock barrels – plus it has an elegant grain. It is a valuable wood when available.