Juglans ailantifolia var. cordiformis Seeds | Heartnut
LATIN NAME: Juglans ailantifolia var. Cordiformis
COMMON NAME: Heartnut, Heart-shaped Walnut
Plant Profile
The heartnut is a Japanese form of walnut whose thin-shelled, heart-shaped nuts usually split cleanly into two unbroken halves. It grows into a tree of ten to twenty metres with a broad, open crown and very large compound leaves up to 90 cm long, each carrying eleven to seventeen leaflets that give the whole tree a tropical, almost tree-of-heaven look. It is native to Japan, Sakhalin and the Kuril Islands, where it grows in moist valley forest, and it reached European and North American nurseries in the 1860s. The nuts ripen in late September inside sticky green husks, and when they are dried the shell is thin enough that a hand-cracker opens it along a seam that runs right around the nut. Kernels come out whole more often than with any other walnut, and they are mild, sweet and free of the bitterness that puts people off black walnuts.
Science & Biotechnology
Juglans ailantifolia var. cordiformis is a variety of the Japanese walnut, and its distinguishing feature is a mutation in shell thickness that has been maintained by selection rather than by any difference in the rest of the plant. The tree is monoecious, with catkins and small female flowers on the same individual, but the two usually mature at different times, which discourages self-pollination. Like all walnuts it produces juglone, a naphthoquinone that is toxic to a range of other plants, and the concentration is highest in the roots, husks and leaves. The variety hybridises readily with butternut, and the offspring, known to growers as buartnuts, combine the heartnut’s thin shell with the butternut’s hardiness and show useful tolerance of butternut canker. That cross is now part of breeding work in North America, where the pure butternut has been devastated by the fungus. Heartnut itself is not immune to walnut blight, which blackens young shoots and nuts in wet springs.
Uses & Benefits
The nut is the point of the tree. Kernels come free of the shell in large pieces, which makes the crop worth gathering by hand, and they are good raw, in baking and pressed for oil. The timber is hard, dark and takes a fine finish, and though the tree is rarely grown for wood alone, an old specimen is worth milling. The husks stain everything they touch and were once used as a dye, and the leaves have a history in folk medicine as an astringent. In a garden the tree is planted for shade as much as for nuts, with the caveat that its juglone will suppress tomatoes, potatoes and many shrubs within reach of its roots. It is also used as a rootstock and in breeding for harder-shelled walnuts. The crop is heavy in alternate years, and a mature tree can bury a lawn in one autumn.
Growing from Seed
Stratify the nuts for three to four months at four degrees, in damp sand or in a sealed bag in the refrigerator, and expect germination in spring; squirrels will find unstratified nuts planted outdoors long before they sprout. Sow two nuts per deep pot, since the taproot must run straight, and cut back to one seedling. Grow them in a nursery row for two years before planting out, and choose the site with the roots in mind: a walnut’s roots extend well beyond its crown and leave a long shadow for other plants. Full sun, deep soil and shelter from late frost are the requirements, and a spacing of eight to ten metres allows the crown to develop. Water well for the first three summers, then leave the tree to find its own water. Prune only in late summer, since walnuts bleed heavily from cuts made in spring.
Our Take
The easiest walnut to crack and the best to eat out of hand, with a shell that opens along its seam. Give it room and no neighbours.
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