The walnut tree is an aristocrat. It grows slowly, lives long, makes no fuss. Then it looks at you with those glossy green fruits hanging from its branches, and you realize you're standing before something truly special. Every single part of this tree — leaves, bark, shell, wood, roots — contains something precious. Or something dangerous. Sometimes both.

What is the walnut tree

The common walnut (Juglans regia) is not native to Italy: it comes from Central Asia and was brought to Europe probably by the Romans or even earlier by the Greeks. But in Italy it found ideal conditions: mild climates, deep and well-drained soils, sunny exposures. Today it is found throughout the country, from Piedmont to Calabria, both in specialized cultivation and as a solitary tree in fields and gardens. The black walnut (Juglans nigra) and butternut (Juglans cinerea) are North American species sometimes used in parks and tree-lined avenues, with similar characteristics but even more prized wood.

The dark secret: juglone allelopathy

The walnut tree has a secret that few know: it secretes from its roots, leaves, and bark a chemical substance called juglone (5-hydroxy-naphthoquinone). Juglone is toxic to many plants: it inhibits their cellular respiration, blocking seed germination and root growth. This is why almost nothing grows under a walnut tree — not due to lack of light (the walnut is a fairly open tree), but because of chemical allelopathy. The plants most sensitive to juglone include apple, pear, tomato, pepper, potato, cabbage, basil, blueberry, and rhododendron. Some plants, however, are resistant to juglone and can grow near the walnut: blackberry, violet, nasturtium, sunflower, and climbing beans. In the garden, this is important to know when planning companion planting correctly.

The fruit: extraordinary news

Walnuts are among the most nutrient-dense foods found in nature. They contain an extraordinary concentration of omega-3 fatty acids (particularly alpha-linolenic acid), antioxidants (including vitamin E and polyphenols like ellagic acid), high-quality proteins, minerals (magnesium, phosphorus, zinc, copper), and B vitamins. Dozens of clinical studies document that regular walnut consumption (even just a handful a day, 30 grams) is associated with reduced cardiovascular risk, improved cognitive function, reduced inflammation, and benefits for intestinal microbiota. The brown skin that wraps the kernel contains the highest concentration of antioxidants: don't remove it. The green hull (the fresh outer skin that indelibly stains hands black) is rich in juglone and vitamin C: it is used in herbal medicine as an astringent and natural dye.

Walnut wood: Europe's most prized timber

Walnut wood is considered one of the most prized in the world for high-quality woodworking. It is hard, stable, easy to work with, featuring beautiful uniform grain and a color ranging from light beige to dark brown. For centuries it has been the preferred material for fine furniture, flooring, paneling, firearms (the wooden stock of luxury rifles was required to be walnut), musical instruments, and craft objects. A mature walnut tree can be worth thousands of euros as timber. Paradoxically, this extremely high economic value of the wood is one of the main threats to the walnut in Italy: many historic specimens are illegally felled for timber, or sold for pittance by owners unaware of their value.

Leaves, bark, and traditional medicine

Dried walnut leaves have been used for centuries in herbal medicine for their astringent, antimicrobial, and antipruritic properties. Preparations made from walnut leaves (infusions, decoctions, mother tinctures) are used externally to treat eczema, fungal skin infections, and excessive sweating. The green bark is a powerful astringent. The walnut shell, finely ground, is a natural abrasive used in cosmetics and as an industrial filtering agent. Almost nothing from this tree is useless.

How to grow and respect the walnut tree near your home

• Don't plant it near the vegetable garden: keep the walnut more than 15 meters away from tomatoes, peppers, potatoes, and the most sensitive fruit-bearing plants. Juglone in clay soils disperses over a wide radius around the roots.
• Walnut harvesting: walnuts are mature when the green hull spontaneously cracks and falls. Collect them from the ground (don't shake the branches), remove the hull as soon as possible (it oxidizes and stains), and let the walnuts dry in a well-ventilated place for 2-3 weeks before storing.
• Storage: shelled walnuts keep in the refrigerator for 3-6 months. Those in the shell last up to a year in a cool place. You can also freeze them shelled: they keep perfectly for a year without losing nutritional properties.
• Eat walnuts as a snack: 30 grams (6-8 whole walnuts) a day is the optimal amount recommended by most nutritional studies. Pair them with fresh fruit for a complete and satisfying snack.
• Watch out for hull stains: the juice from the green hull stains skin and fabric a dark brown that is practically impossible to remove. Wear rubber gloves when collecting and shelling fresh walnuts.
• Observe who visits the walnut tree: squirrels and jays love walnuts and bury hundreds as winter stores. Many of these are forgotten and germinate the following spring — this is how the walnut naturally spreads through the landscape.

If you have a walnut tree in your garden or field, you have a treasure. Don't think only of the wood or the walnuts: think about how many decades it took to grow this large, and how many more will be needed. Treat it accordingly.