It is often claimed that walnuts were one of the first food crops to be cultivated by human beings. Their history is certainly a long one, with its roots reaching back to ancient Persia. The Romans regarded the nuts as food of the Gods, while when first imported into the United Kingdom walnuts were reserved for royalty alone. In the U.S. walnut cultivation is thought to date back to the late 1700s.
And it’s not just history that walnuts are rich in. They are also nutritious, being one of the best plant-based sources of omega-3 acids, which help the brain function. They also contain good levels of fiber, protein and antioxidants.
Growing your own walnut tree can seem a little daunting, as they are long living – with some having the potential to last up to 200 years – and don’t produce a reliable harvest for about a decade. But planting a walnut tree brings other benefits to the site, with its tall, broad canopy attractive to wildlife and capable of significant windbreak and shade capacity. The walnut is also an attractive tree, setting small bright flowers in spring. Furthermore, planting a walnut tree is an investment in the future. It is a refutation of the ‘more, now, quicker’ society in which many people live, and a contribution to both the biodiversity and food production potential of the site for many years to come.
There are tow main types of walnut that are cultivated by both commercial farms and gardeners: the Black walnut and the English walnut. The Black varieties are more common in the U.S. while the English version is more often found in Europe, particularly around the Mediterranean. There are hundreds of cultivar varieties within each of these types. Research native varieties and visit local growers to see which are suited to your soil and climate conditions.
Depending on the species, walnut trees can grow up to 25 meters tall, and most have broad, spreading canopies. Ensure that you leave enough room for the mature tree to grow into. As a general rule, leave at least 12 meters between specimens. Walnuts like a protected site that does not experience strong winds or frosts, but which gets several hours of full sun. Walnut trees prefer temperate climates that do not have too high temperatures during the summer, but which experience a reasonably cold winter. The leaves that fall from a walnut tree have chemicals within them that can be toxic to other plants, including grass, so avoid planting where the canopy will overhang other species.
Walnuts are quite hardy and will tolerate most soils, but do best on soils that are rich in organic matter to a deep level – to help the long-lasting roots anchor the tree – and well drained. The ideal soil pH for a walnut tree is neutral.
Plant in the fall or winter. You can plant either seeds or a juvenile tree. Seeds must be sourced from an organic supplier – you can’t simply plant a nut from the supermarket. Seeds can be planted three inches below the surface, while a young tree should be planted in a hole three times as wide as the root ball, and backfilled so that no soil covers the trunk. It can be useful to stake a juvenile tree for the first year or two to promote good establishment.
Apply organic compost in early spring, and mulch with straw or bark chips to help preserve soil moisture. Avoid adding compost during the summer as this can encourage late growth that will then be susceptible to winter frosts. Water juvenile trees whenever they need it during the spring and summer (check the soil six inches below the surface, and if dry and crumbly, irrigate). If you want to encourage your walnut tree to bush rather than attain height, prune the leader branch in early fall to encourage secondary growth. Remove any dead or decaying branches whenever you spot them.
Most walnut trees will not provide any harvestable crop until somewhere between the eight and tenth year of growth. At this early stage in their development, the crop will not be especially plentiful; it is only really after the twentieth year that the walnut tree enters full production. The height of a mature tree effectively means that you will be harvesting walnuts that have fallen to the ground – this helps to protect the branches from damage, and the protective casing of the nuts mean they are not damaged by the fall. Walnuts grow surrounded by a leathery, fibrous casing that is green in the first instance but which turns black or brown when ripe, depending on the species. And you want to look for fallen nuts that have splits in the casing. Test a few – wearing gloves as ripe walnuts can stain skin and clothes – to check whether the nut inside is fully formed and comes away easily from the casing when broken open. If so, the majority of the nuts on the ground are likely to be ready for harvest.
Wearing rubber gloves to prevent staining of the skin, remove all trace of the fibrous coating – a wire brush can be useful for this task – then rinse the nuts well in water to remove the tart tannins. Dry the nuts, either in a very cool oven for 24 hours or so, or in a warm, well-ventilated place for a couple of weeks. Once dry, store the nuts in an airtight container.
It can be tempting to throw the walnut shells into the compost pile or use them as mulch on garden beds. However, caution is advised as walnuts contain a chemical called juglone, which can be toxic to some fruits and vegetables, such as tomatoes. While a few shells shouldn’t cause a problem, if you have a large harvest, you should seek another form of disposal. Walnut shells are often used in industrial cleaning products, so you may seek to contact an organic producer to sell your shells.