Juglans hopeiensis Seeds | Hopei Walnut

Matched pair of deeply ridged Hopei walnut shells resting on dark wood — Hopei Walnut (*Juglans hopeiensis*): Juglandaceae, hills of northern China.

LATIN NAME: Juglans hopeiensis

COMMON NAME: Hopei Walnut

Plant Profile

Hopei walnut is grown less for its kernels than for its shell. The nut is large, thick-walled and carved into deep, irregular ridges, and a perfectly matched pair is worth more than a sack of ordinary walnuts, because these are the shells that are rotated in the hand as wenwan. The tree itself is a broad, open grower to twenty metres, with long pinnate leaves, a stout trunk and grey, furrowed bark. It does best on deep, well-drained, sunny ground in the hills north of the Yellow River, where the winters are hard and the summers dry. The leaves are large and drooping, and the nuts sit in thick green husks that split late in the season.

Science & Biotechnology

The taxonomic position of Juglans hopeiensis has been argued for a century. It was described from Hebei in 1934 and is now widely read as a stabilised hybrid between the common walnut and the Manchurian walnut, J. regia and J. mandshurica, which would explain both its intermediate leaves and its partial sterility. Populations are small and scattered, and the trees are largely maintained by grafting rather than by seed. That matters commercially, because seedlings do not come true and the character of a shell is a clone character. Wild trees are protected in China, and the best shell types are propagated vegetatively. Because the species is probably of hybrid origin, its seed is genetically variable, and growers who want a particular nut shape should buy grafted plants rather than seedlings.

Uses & Benefits

Its use is cultural as much as culinary. Pairs of shells are matched by size, symmetry and ridge pattern, then worked in the hand for years until the surface darkens and polishes, and the best pairs change hands for serious money. The kernels are edible but small and fiddly. As a tree, it is a tough, drought-tolerant walnut for a large garden or an orchard edge, and it is grafted onto common walnut rootstock in nursery practice. The timber is dense and takes a good finish, though the tree is too valuable standing to cut for it. Shells are also carved, and the offcuts of the trade go to small ornaments and buttons.

Growing from Seed

Seed is a gamble, because the parent is probably a hybrid and the seedlings will vary in shell and vigour. Stratify the nuts for three months at two to five degrees, sow two to three centimetres deep in spring, and expect germination over four to six weeks. If a particular shell is wanted, graft onto common walnut in late winter instead, since that is the only way to fix the pattern. Give the young tree full sun, deep soil and a stake for the first two years, and keep the ground clear of grass around the trunk. Water young trees in dry summers for the first three years, then leave them alone.

Our Take

A walnut you grow for its shell, not its kernel, and one that has to be grafted if the shell is to be worth having. The tree is ordinary; the nut is the point.

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