Juglans regia, the Persian walnut, English walnut, or especially in Great Britain, common walnut, is an Old World walnut tree species native to the region stretching from the Balkans eastward to the Himalayas and southwest China. The largest forests are in Kyrgyzstan, where trees occur in extensive, nearly pure walnut forests at 1,000–2,000 m altitude—notably at Arslanbob in Jalal-Abad Province. It is widely cultivated across Europe.
Juglans regia is a large, deciduous tree attaining heights of 25–35 m, and a trunk up to 2 m diameter, commonly with a short trunk and broad crown, though taller and narrower in dense forest competition. It is a light-demanding species, requiring full sun to grow well.
The bark is smooth, olive-brown when young and silvery-grey on older branches, and features scattered broad fissures with a rougher texture. Like all walnuts, the pith of the twigs contains air spaces; this chambered pith is brownish in color. The leaves are alternately arranged, 25–40 cm long, odd-pinnate with 5–9 leaflets, paired alternately with one terminal leaflet. The largest leaflets are the three at the apex, 10–18 cm long and 6–8 cm broad; the basal pair of leaflets are much smaller, 5–8 cm long, with the margins of the leaflets entire. The male flowers are in drooping catkins 5–10 cm long, and the female flowers are terminal, in clusters of two to five, ripening in the autumn into a fruit with a green, semifleshy husk and a brown, corrugated nut. The whole fruit, including the husk, falls in autumn; the seed is large, with a relatively thin shell, and edible, with a rich flavour.
Prefers moist, organically rich, well-drained soils in full sun. Intolerant of shade. Difficult to transplant because of deep taproot. Although young trees will sometimes begin producing nuts when only 4-6 years old, it usually takes 20 years before a tree will produce a large crop of nuts. Does not perform well in the hot and humid deep South where, as nut trees go, pecans (see Carya illinoinensis) generally do better.
Native to Asia and southeast Europe (Balkans), English walnut (or Persian walnut ) is a deciduous tree that typically grows 40-60’(less frequently to 100’) tall with and a spreading rounded crown. This is the tree that is grown commercially in the West Coast states for the walnuts that are sold in stores. It is also grown ornamentally in many parts of the U. S., and is valued for its fine-grained wood that is used to make cabinets, furniture and gunstocks. Bark is gray and smooth. Odd-pinnate compound leaves (to 16” long), each with 5-7 (infrequently to 13) oblong leaflets. Leaves are late to emerge in spring and early to drop in fall. Leaves are strongly aromatic when crushed. Fall color is an undistinguished yellow. Yellowish green monoecious flowers appear in late spring (May-June), the male flowers in drooping hairy catkins and the female flowers in short terminal spikes. Female flowers give way to edible nuts, each being encased in a smooth green husk. Nuts mature in autumn. Nuts are thin-shelled, making the kernels easy to extract. Juglans comes from the Latin words jovis and glans meaning nut of Jove. Regia means kingly, in reference to the superior quality of the nuts. Many cultivars of this species are available in commerce.
No serious insect or disease problems. Potential diseases include anthracnose, bacterial blight, root rot, canker, leaf spot and shoot dieback. Watch for fall webworm and a variety of foliage chewing caterpillars. English walnut roots produce chemicals called juglones which are very toxic to certain other plants such as azaleas, rhododendrons, blueberries, peonies and solanaceous crops (tomatoes, peppers, potatoes). Most of the toxicity is limited to within the drip line of the tree, but the area of toxicity typically increases outward as the tree matures. Nuts can be quite messy in fall.
Large deciduous tree for large landscapes. Nuts may be harvested. Inappropriate as a street tree.