Walnuts are very easy to grow, and in time will make large, imposing trees. Although requiring less maintenance than other orchard trees, there are some things it is useful to know when deciding on the right tree for you.
The botanical name for the common walnut is Juglans regia. Originally native to Southern Europe, Iran, China and parts of the Himalayas, it has been planted widely across the globe. Alexander the Great introduced it to Macedonia in the 4th century BC, the Romans planted walnuts throughout Europe and Northern Africa, and English colonists took it to America in the 1700's.
The black walnut (Juglans nigra) is native to much of North America, where it has been grown as an important timber wood for centuries. Introduced into the UK in the first half of the 17th century, possibly by the botanist John Tradescant the Younger, it has been used as a forestry tree in the south of the country, but has mainly been planted as a fine parkland specimen. It does produce edible nuts which have a slightly stronger flavour than thos of the common walnut, but they have often been thought of secondary importance.
Walnuts work best as standalone trees - other species planted underneath or very close by will often struggle. There is evidence of allelopathy (walnuts produce a biochemical called juglone in their leaves and fruit which is reputed to inhibit the growth of competing plants), but this is contested. In any case, such a fabulous tree deserves plenty of space, taking the spotlight in centre stage.
Walnuts thrive in sunny, open situations. They can live to over 200 years old, and in time will grow to 20m or more, so allow plenty of space!
In theory, they are self-fertile, but the male and female flowers open at slightly different times so cross-pollination for a single tree is not always guaranteed.