At the present time, the black walnut is regarded as being of greater promise for planting in the northern states than is any other species either native or introduced.
The Japanese Walnut
To a considerable extent this species has been confused with the Persian walnut, although the two are quite unlike. This is a dwarfish species with dull green rough leaflets often as many as 15 or 17 per leaf, which often bears nuts in clusters of a dozen or more. While green the outer hulls of the nuts are rough, and somewhat sticky.
The Persian walnut is a standard-sized upright growing tree with bright green leaflets, usually 5 to 7 per leaf, and smooth, round nut hulls which split open and shed the nuts automatically.
The Japanese walnuts hybridize freely with other species of walnuts and produce nuts of all types; not infrequently crosses of this kind resemble butternuts so closely as to be practically indistinguishable from them.
True Japanese walnuts have a range in form of two distinct types. The better known is of guinea egg shape; the other, often known as the heartnut, is of distinct heart shape. Neither is large; the former is of about the size of a guinea egg or smaller; the latter is still smaller. Both are like the black walnut in being encased in a rough outer husk, which upon maturing shrivels and adheres to the surface of the nut. The shells are thinner than are those of the black walnut, but thicker than are those of the Persian walnut. When well matured, the shell of the heartnut tends to open slightly at the apex, after which it can be readily split in half with a knife blade. The flavor of the kernel is much like that of the American butternut.
The Japanese walnut is ordinarily hardy wherever the black succeeds. It is by no means uncommon in Michigan where it is especially appropriate for family planting. For the present, seedling trees will have to be relied upon almost wholly, as very few varieties have been propagated. So far as the writer is informed, the only named variety available from a northern nursery is the Lancaster introduced by J. F. Jones, a nurseryman at Lancaster, Pa.
Persian Walnut
Perhaps no species of nut tree has attracted as great attention in Michigan as has the Persian walnut. Under some conditions it does well for a time in the eastern or northeastern states, but on the whole its performance is distinctly erratic. Commercially speaking, it is of importance in this country only on the Pacific coast. Trees on the campus at Michigan Agricultural College and at many private places in the central part of the state, have come to little. Usually they grow well in summer only to freeze back nearly as much in winter. In Saranac County, eastern Michigan, close to Lake Huron there are a few young orchards that are in good condition, but a half mile back from the lake the results are discouraging. The same is true next to Lake Michigan from Grand Rapids south to the Indiana line.
The only recommendations that can be made relative to planting the Persian walnut in Michigan are, that it be planted very cautiously in any part of the state and except under very favored circumstances it be not at all in the middle of the state.