Japanese Walnut (Juglans ailanthifolia)

At a glance

Lifecycle: Perennial (hardy)
Exposure: Full sun
Frost limit: −34.4 °C

Cultivation

Requires a deep well-drained loam and a sunny position sheltered from strong winds. This is the hardiest member of the genus, capable of growing in all areas of Britain. The young growth in spring, however, can be damaged by late frosts. This species is cultivated for its edible seed in Japan, it has the potential for producing very superior nuts, especially if hybridized with J. cinerea. Plants produce a deep taproot and they are intolerant of root disturbance. Flower initiation depends upon suitable conditions in the previous summer. Any pruning should only be carried out in late summer to early autumn or when the plant is fully dormant otherwise wounds will bleed profusely and this will severely weaken the tree. Trees have a dense canopy which tends to reduce plant growth below them. We have no specific information for this species, but the roots of several members of this genus produce substances that are toxic to many plant species, especially apples (Malus species), members of the Ericaceae, Potentilla spp and the white pines (certain Pinus spp.). The leaves of many species also secrete substances that have an inhibitory affect on plants growing underneath them. All in all this is not a very good companion plant[K].

Propagation

The seed is best sown as soon as it is ripe in individual deep pots in a cold frame. You need to protect it from mice, birds, squirrels etc. The seed usually germinates in late winter or the spring. Plant out the seedlings into their permanent positions in early summer and give some protection from the cold for their first winter or two. The seed can also be stored in cool moist conditions (such s the salad compartment of a fridge) over the winter and sown in early spring but it may then require a period of cold stratification before it will germinate.

Edible uses

Seed - raw, cooked or used in confectionery. An edible oil is obtained from the seed, but it tends to go rancid quickly. Young buds (flower?) and fruit stalks - cooked.

Medicinal uses

The bark is anthelmintic, astringent, diuretic, lithontripic, pectoral, skin, tonic (kidneys).

Material uses

A brown dye is obtained from the seed husks and the bark. Rich in tannin, it does not require a mordant. The bark is rich in tannin. It is used as a dye and also medicinally. Plants produce chemicals which can inhibit the growth of other plants. These chemicals are dissolved out of the leaves when it rains and are washed down to the ground below, reducing the growth of plants under the tree. Wood - soft, light, not easily cracked, of good quality. Used for cabinet making etc.