Dr. J.A. Neilson, Michigan

The Japanese walnut, Juglans sieboldiana (ailantifolia*), and its varietal form cordiformis, were said to have 'been introduced into America from Japan about 1870 by a nurseryman at San Jose, California. From this and other subsequent introductions a considerable number have been grown and distributed in the United States and Canada.

A recent inquiry by the writer brought forth some interesting data relative to the occurrence and distribution of this species in North America. This inquiry shows that it has been widely distributed. and is reported in the following states: Arkansas, Arizona, Alabama, Connecticut, California, Delaware, Illinois, Iowa, Indiana, Kentucky, Massachusetts, Missouri, Minnesota, Maryland, Maine, Mississippi, Michigan, New Jersey, New York, New Hampshire, Ohio, Oregon, Pennsylvania, Rhode Island, Vermont, Virginia, West Virginia, Washington, and Wisconsin. No reports were received from Carolina, Louisiana, Montana, North Carolina, North and South Dakota, Idaho, Georgia, Colorado, Kansas, Texas, and Wyoming, and negative reports were received from Florida, New Mexico, Nevada, Oklahoma, and Tennessee.

In none of these states is the Japanese walnut abundant in the same degree as other kinds of nut trees, but in some states it was reported more frequently than in others. It occurs more abundantly in Pennsylvania, New York, Connecticut, New Jersey and Delaware than in other states.

In Canada it has been reported, from Prince Edward Island, Nova Scotia, New Brunswick, Quebec, Ontario, Manitoba, Alberta and British Columbia. In Ontario it is found occasionally from Windsor to the Quebec boundary and from Lake Erie to North Bay. There are several fine large trees in southern Ontario, some of which are worthy Of Propagation. Many of the trees in Ontario and other eastern provinces grew from nuts distributed by the writer several years ago. For five years in succession the writer bought the crop from a. large heartnut tree near Jordan Station, Ontario, and distributed the nuts all over Canada to those who were interested. More than twelve thousand nuts were thus distributed and I know from observation and reports that seedling trees are now growing from the Atlantic to the Pacific. I am going to tax your credulity to the utmost and tell you that one of my correspondents reports heartnut trees growing in the Peace River area of northern Alberta. 1 have no recent report from my friend but 1 know that the trees came through two winters in that far northland.

Possibly in the days to come a superior seedling or a hybrid may be found in these numerous seedlings which will be worth propagating. Some of these trees have already borne nuts and many have made very good growth.

The Japanese walnut has also been reported from New Zealand and several states in Australia, England, France, Germany and other European countries.

Climatic Adaptation

From the foregoing it can be seen that this species of walnut has been widely distributed and is now growing in countries with a wide temperature range. Reports are on hand which show that the trees have endured temperatures of 40 below zero F. to 110 above zero. From this it need not he assumed that all Japanese walnut trees will stand great extremes of heat and cold, for experience shows that they will not. It does show, however, that some individuals at least have marked hardiness to cold and bent and have endured temperatures much greater than the English walnut. The best results in growth and fruitfulness have been obtained in those regions of moderate rainfall where the apple and sweet cherry grow successfully.

Soil Requirements

The Japanese walnut seems to thrive on many soil types ranging from a heavy clay to a light sand, but does best on what is popularly known as a well drained fertile sandy loam with a friable clay subsoil. lt will not do well on strongly acid soils and those who have planted trees on such soils should apply lime in liberal quantities. Poorly drained soils or very light soils deficient in humus are also not suitable.

Tree and Nut Characteristics

The Japanese walnut has several characteristics which make it desirable as an ornamental and as a nut-bearing tree. It grows rapidly, has large numerous luxuriant leaves which give it a tropical effect, and usually has a symmetrical outline. It bears early, sometimes in the second year from the graft, yields heavily and is often reported to yield regularly.

A heartnut tree owned by Mr. Silvester Kratz of Jordan Station, Ontario, produced nearly seven bushels of husked nuts one season and Mr. J. W. Hershey reports a yield of ten bushels of heartnuts from a tree near Olney, Pennsylvania. He also reports a cash return of $50.00 from one tree grown by Mr. Killen of Felton, Delaware. These were heartnuts and sold for 50 to 75 cents a pound. Mr. J. U. Gellatly, Westbank, B. C., obtained a yield of ten bushels of unhusked nuts from a heartnut tree of medium size. The yields from the common type, J. sieboldiana, have also been heavy, but since no figures are available no definite statements can be made.

In the Japanese walnut as in other species of nuts there is marked variation in nut characteristics, such as size, thickness of shell, cracking quality, extraction quality and flavor of kernel. Heartnuts have been found ranging from ½" to 1 ¾" in length. The largest heartnut I have ever seen came from Gellatly Brothers of Westbank, B.C. This nut was 1 3/4 in. long by 1¼ in. wide and was fully 1 in. thick. 1 also located a fine Sieboldiana type which is said to be the largest. found up to date.

Some of these good kinds possess excellent cracking and extraction quality. Mr. John Hershey of Downingtown, Pa., reports several good easy-cracking strains not yet introduced and Mr. Gellatly has one called 0. K. that can easily be cracked with a hand nut cracker. I have also found one that 1 believe is a hybrid and which has excellent cracking and extraction quality. These specimens came from a seedling heartnut grown by Mr. Claude Mitchell, Scotland, Ontario. The nuts are longer than any heartnut found so far. The kernels in many cases fall out whole or in halves. This strain received the 0. K. of Prof. Reed and Dr. Deming and as you know when a nut gets by either of those gentlemen it has to possess some merit. The good result produced. by nature without any assistance from man suggests the possibility of getting even better results from parents of superior characters. I. believe the Japanese walnut offers interesting possibilities in breeding with the butternut and possibly the black and English walnut. Definite plant breeding work should be done with these species as well as with all other species of nuts.

The Japanese walnuts generally grow fast but usually do not attain a large size. In most cases the trees rarely grow more than 35 feet tall with a spread of 30 to 50 feet, but occasionally specimens attain much larger size. The writer saw a heartnut tree on Mr. Kratz's farm near Jordan Station, Ontario, which had a trunk diameter of 2 ft., a height of 35 ft., and a spread of 64 ft. Near St. Thomas, Ontario, there is a large sieboldiana tree which is 75 ft. across the top and is about 45 ft. tall. Mr. Ricks. reports a huge tree near Olney, Pennsylvania, that is 80 ft. across the top and 60 ft. tall and Dr. Deming reports a tree with a spread of 100 ft.


Through the efforts of the Northern Nut Growers Association members several good varieties have been found and propagated. These varieties have been widely distributed but have not been extensively planted. The results are variable is might be expected, but generally the reports are satisfactory. In the eastern states the following varieties seem to do reasonably well: Faust, Bates, Ritchie and Stranger. In British Columbia, Messrs. J. U. and David Gellatly have located several very good strains such as Gellatly, 0. K., Calendar, Walters and Rosefield. These newer varieties from the West have several good characters and are worthy of a wider trial in the East.

Diseases and Insect Pests

In common with most other forms of plant life the trees are susceptible to some insects and diseases. Reports of injury by the walnut weevil, Conotrachclus juglandis, and also, by codling moth larvae have been received. In some cases the foliage is attacked by rust fungi and some injury is also done by leaf spot. Prof. Reed reports witches broom attacking some trees in the south and one case of this disease was observed by the writer in Ontario on a Siebold-butternut hybrid. Notwithstanding these defects it is believed that the Japanese walnut is less attacked by disease and insects than most other species of nut trees.

Opinion of Observers

The opinion of a group of people on the merits or defects of a tree species or project is worthy of consideration. In order to get an expression of opinion as to the merits of the Japanese walnut the following question was asked: Do you consider the better strains of Japanese walnut worthy of more extended planting? The answers to this inquiry were numerous and varied. The great majority were in favor of increased plantings but a few were somewhat dubious. Nearly every one agreed that the species possessed marked beauty and was worthy of more extended planting as an ornamental. Some gave preference to the nuts over the black and English but the majority thought the quality was not quite up to the standard of these two species. Some observers reported favorably on the heartnut for culinary purposes and as an ingredient of ice cream and candy. With these latter comments I have had personal experience and can heartily agree.


From the evidence furnished by correspondents and from personal observation, the good qualities of the Japanese walnut may he summed up as follows: Rapid growth, marked beauty of form and foliage, early bearing, productiveness, and more than average hardiness to winter cold. The nuts from superior trees are easier to crack than the butternut, hickory and black walnut, but not so easy as the pecan and Persian walnut.

These superior varieties yield nuts with a mild f1avor which appeals to the taste of many people, but others think the flavor is not quite pronounced enough.

This species crosses readily with the butternut and offers interesting possibilities for the plant breeder.

The trees appear to be somewhat less susceptible to insects and diseases than other walnuts, but this may not always hold good.

The defects of the Japanese walnut most frequently mentioned are lack of flavor and pollination deficiencies. Some trees produce staminate flowers too early for proper pollination and thus do not yield a crop unless another good pollinator grows nearby.

Susceptibility to sun-scald and to San Jose scale are some other weaknesses. Many of the trees commonly grown are undesirable because of small size of nuts, poor cracking quality and too mild a flavor.

A careful consideration of the good and bad. characters of Japanese walnuts suggests the following program before the culture of this species can be placed on a sound basis.

  1. A systematic and thorough search of the United States and Canada for productive trees yielding nuts of large size, of good cracking and extraction quality and pleasing flavor.
  2. The propagation and wide dissemination of these superior strains to members of the Northern Nut Growers Association and particularly to experiment stations where there seems to be a striking lack of information on this and other species of nuts.
  3. Systematic improvement by means of hybridization with the butternut and other suitable species.

A program such as this would yield. information of great value and would probably establish the culture of this species on a sounder basis than it now is.. Until this has been done the logical course to follow is to plant the best varieties in limited numbers in areas where the black walnut thrives and even in areas too cold for the black walnut.

* current nomenclature

Reported in the 21st Annual Report (1930) p. 39-45.

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