Some Notes on the Hardiness of the English Walnut in Michigan and Ontario

By J. A. Neilson, Michigan

In a study of the desirable characters of nut trees for planting in the northern part of the United States and in southern Canada, one is forced to place hardiness first. Rapid growth, high yield and excellent quality of nuts are of little value if hardiness is lacking. Hardiness, of course, is a relative term and may be applied to disease and insect resistance, adaptability to diverse soils and capacity to withstand extremes of winter and summer temperatures. In the present paper emphasis will be placed on resistance to winter cold and to unusual weather conditions, such as occurred during the autumn of 1933 and the winter of 1933 and 1934.

In order to properly understand the effect of the past winter on the English walnut, it will be necessary to devote some attention to the weather conditions that prevailed in the southern half of Michigan in the autumn of 1933. A perusal of the meteorological records shows that the average maximum and minimum temperatures in September and October were unusually high and that there was a heavy rainfall in these two months. The following table shows the precipitation and temperatures recorded at the Kellogg Farm where most of our nut cultural experiments are conducted.

September—The average maximum temperature, 79.1; average minimum temperature, 55.7; precipitation, 4.55 inches. October—The average maximum temperature, 60.1; average minimum temperature, 38.4; precipitation, 6.81 inches.

The unusually high temperatures and heavy rainfall caused growth to continue much later than normally and thus prevented the wood from ripening properly before winter set in.

English walnuts are found at several places throughout the lower peninsula and more particularly in the southern half of the state. In no place, however, are the trees numerous with the exception of a small area around Lexington, where there are approximately 100 trees. Inasmuch as this paper deals with the effect of low temperatures on the English walnut, the minimum temperatures of the weather station nearest to the places mentioned in the following text are given hereunder.

Lowest

PlaceMo.-DateTemp.

AlleganFeb. 9-19

Bay CityFeb. 9-20

CaroFeb. 9-30

CroswellFeb. 9-26

FennvilleFeb. 9-20

FlintFeb. 9-15

Grand RapidsFeb. 9-16

Gull Lake—Kellogg FarmFeb. 9-18

HartFeb. 9-22

LansingFeb. 9-18

Mount PleasantFeb. 9-21

MuskegonFeb. 9-16

OwossoFeb. 9-20

SaranacFeb. 20-25

SpartaFeb. 9[A]-22

Leamington, Ont.Feb. 9-18

GuelphFeb. 9-30

SimcoeFeb. 9-30

The extreme cold of the past winter following a warm, wet autumn caused a great deal of injury to English walnut trees in this state and elsewhere. The data presented herein were obtained by a careful examination of several plantations or individual trees scattered over the southern half of the lower peninsula in Michigan and in southwestern Ontario. To properly present this information it seems desirable to group the varieties or strains according to their place of origin.

Group 1. Cultivated Varieties from the Pacific Coast.

In this group we have Mayette, Franquette and Seeando. The Mayette has been considered one of the hardiest of the cultivated varieties and was therefore included in the plantings at the Kellogg Farm. More than twenty trees were planted and every one died last winter or in the preceding winter. Seeando, a new and supposedly hardy variety from Washington state, was planted in limited numbers in the spring of 1933, but every tree perished last winter. Franquette was not planted as a nursery tree, but was top-grafted on several large black walnuts at the Kellogg Farm and at East Lansing, Michigan. The grafts made a vigorous growth but only two out of eleven lived through the winter. In Simcoe, Ontario, where the minimum temperature was -30F, a six-year-old tree was so badly injured that it will likely die this winter, but should it not perish, the degree of injury is so severe that it will be of very little value. In the Niagara district the Franquette top-grafted in 1926 on black walnut came through in moderately good condition, but in this part of Ontario the minimum temperature was only 10 below zero F.

Group 2. New Varieties of Canadian Origin.

This group contains Broadview and McDermid. Broadview scions were secured from Mr. J. J. Gellatly of Westbank, B. C., who discovered the variety near Broadview, B. C. These scions were grafted on a medium-sized black walnut in 1931 and have since made a remarkable growth, but notwithstanding the vigorous growth there was no killing back during the past winter or in preceding winters. This variety was also grown as a top-graft by Mr. Carl Walker of Cleveland Heights, Ohio, where the minimum temperature last winter was -26 degrees F. Some killing back was reported on this tree, but the injury was not severe enough to be serious. The Broadview is reported to have endured without injury -25 degrees F. in British Columbia and in Russia, where the parent tree originated, equally low temperatures are said to prevail. The McDermid was obtained from Mr. Peter McDermid of St. Catherines, Ontario. This tree is a third generation tree in Ontario and is descended from a tree brought out from Germany more than 100 years ago. The nuts are large with a moderately thick shell and contain a kernel of excellent quality. McDermid has been grown as a top graft at Simcoe, Ontario, East Lansing, the Kellogg Farm and Estate near Augusta and at South Haven, Michigan. All of the trees of this Variety grown in Michigan came through without injury, but the tree at Simcoe, Ontario, suffered somewhat by killing back of the past season's growth. The larger branches and trunk, however, were uninjured and have since made a rank growth. The McDermid top-grafted on a black walnut on Mr. G. Tolles' farm at South Haven proved hardy and was one of the few English walnut trees in Michigan to bear nuts this year.

At the Michigan State College where the temperature went to -18 degrees F. vigorous McDermid grafts on a thrifty black walnut were uninjured whereas all the Franquette grafts on the same tree were killed outright. Similar results were noted on several trees at the Kellogg Farm near Augusta, Michigan.

Group 3. Carpathian Walnuts.

This strain of Juglans regia was introduced into Canada by Rev. P. C. Crath of 48 Peterboro Avenue, Toronto, Ontario, from the Carpathian mountains in southeastern Poland. In this part of Europe the winter temperatures are reported to go to -20 degrees F., and occasionally lower. In the winter of 1928-29 a vast amount of injury was done to fruit trees and the less hardy English walnut trees in Poland, but a number of English walnuts came through without serious injury. Scion wood of some hardy selections was sent in 1932 to the writer by Mr. Crath, who was then in Poland. This material was grafted on vigorous growing black walnuts in the spring of 1932 and good results were secured with two varieties. These varieties made a vigorous growth, but notwithstanding this they showed not the slightest injury in the spring of 1934. The growth made during the summer of 1934 has been remarkable and if this unusually vigorous growth survives the coming winter it would seem as though we have an exceptionally hardy strain. The nut characters and productiveness of these varieties have not yet been determined in Michigan, but if they are equal to some of the trees of the same origin, then we will have very valuable trees. These strains have been named Crath and are distinguished by Nos. 2 and 5.

About 100 small seedlings of Polish origin were purchased from Mr. Landega of Toronto, Ontario, an associate of Mr. Crath, and planted at the Kellogg Farm in 1932. These trees have been subjected to trying conditions through drouth, competition with alfalfa, late growth and severe winter temperatures. As a result some have died, but a number are growing nicely, and it is expected that some of these will eventually become established. Seedlings of this lot suffered only slight injury near Sparta, Michigan, but grafts from these same seedling trees set on a vigorous young black walnut were very severely injured. Another tree from this group endured the severe cold at Madison, Wisconsin, during the past winter and made a rapid growth this season.

Scions from another fine tree of Polish origin growing at Mr. Crath's place in Toronto were set on several trees in this state in the spring of 1933 and in every case endured the lowest temperature without much injury to the new growth. A very unusual condition was noted, though on three young black walnut trees top-grafted to scions of this tree. On these trees the vigorous grafts appeared to be uninjured in the wood, but the bark at the point of union on both stock and scion was so severely injured that the grafts died. An examination showed evidences of bark splitting and this was undoubtedly caused by a severe and sudden cold spell following a very late and extremely vigorous growth. Scions of this strain were grafted on a medium sized black walnut at Caro, Michigan, and these endured -30 degrees F. without serious injury. A small black walnut tree at the Kellogg Farm top-grafted to scions of another Crath seedling showed bark injury on the lower half of the stock, but fortunately the extent of the injury was not great and the graft was saved. It also made a vigorous growth this season notwithstanding the hot dry weather and injury to the bark on the stock. Scions of this strain were grafted on a vigorous black walnut on the farm of F. Wilde at Wayland in 1933. These scions made an extraordinary growth that season and were subjected to a temperature of -20 degrees F. last winter. Some killing back occurred but no permanent injury was done as the grafts have made a good growth this season.

Pomeroy Seedlings

This strain of walnuts originated on the farm of Mr. Norman Pomeroy of Lockport, New York. Trees from this plantation, or seedlings of these trees, are grown at various places throughout Michigan with the heaviest concentration near Lexington. There are also a number of Pomeroy seedlings on the farm of Mr. Grant Fox at Leamington, Ontario. All of the trees in the Lexington district were more or less severely injured by killing back of the branches and occasionally by bark splitting or bark killing. At St. Louis one very fine tree was nearly girdled by bark injury and will undoubtedly die. Near Ithaca another tree showed moderate killing back and in the city two trees were killed to the ground and one other so severely injured as to be useless. The trees at Leamington, Ontario, were also severely injured, especially those that bore thin-shelled nuts. Some of the larger trees in this plantation which bore nuts with moderate thick shells were not as severely injured, and this would seem to indicate that there may be a relationship between thickness of shell and resistance to winter cold.

In this plantation it was also found on another occasion that the trees which bore thin-shelled nuts produced long vigorous succulent shoots with a large pith and loose, spongy buds. On the other trees that bore thick-shelled nuts the shoot growth was shorter and firmer than on the trees with thin-shelled nuts. In contrast to these trees the buds on the Crath trees Nos. 2 and 5 were short, rather broad and very solid. The wood also was very hard and well matured with a small pith even on vigorous shoots. This seems to indicate that there may be a relationship between density and maturity of wood and buds and winter hardiness.

Other Seedlings

At various places in Michigan there are English walnut trees that originated in England or which are seedlings of trees that came from England. An exceptionally good tree of English origin grows near Ionia and is called Larson after the owner of the farm on which it grew. The Larson tree is at least 50 years old and bears nuts of large size and excellent quality in favorable seasons. This variety was propagated for the college by the Michigan Nut Nursery and some of these trees were planted at the Kellogg Farm in 1933. Unfortunately the past winter killed all the young trees and so severely injured the parent tree that its recovery is doubtful. Beck is another good variety of English origin that grows near Allegan on the Monterey road. The original tree of this variety was very severely injured and much greater injury was noted on seven-year-old grafts of this variety which had been set on a black walnut. At Vassar there is a tree of English origin that yields very fine nuts, but this one was also severely injured. Near Conklin there is an old tree of German origin and this was likewise severely injured, but not so much as the trees from England.

Chinese Walnuts

The Chinese walnut is a geographic form of the so-called English walnut. It occurs over a large area of central and northern China, and it is believed that trees from the northernmost range of this species in China are somewhat hardier than the average English walnut from western Europe. The number of trees of this species under observation is very limited, but those that have been seen appear to be promising. The largest and best tree observed grows on the property of Mr. Geo. Corsan at Islington, Ontario. This tree was subjected to -26 degrees F. last winter and was somewhat injured. The growth this spring was delayed longer than normally and some killing back was noted. Eventually the tree started to grow and made a normal amount of growth. Scions from this tree were grafted on two black walnut trees at the Kellogg Farm in 1933 and a vigorous growth was made in that season. These grafts were carefully examined in the spring of 1934 and were found uninjured. Subsequently a very large graft on one medium sized black walnut tree died, but this was due to injury at the point of union rather than to the graft above. The remaining scions made a good growth this season. Seedling trees of another strain of Chinese walnut showed some variation in their hardiness. Some came through in good condition and made a vigorous growth but others were more or less injured. The limited number of trees under observation scarcely justifies definite conclusion, but it would seem as though this form of Juglans regia is worthy of a wider trial in southern Michigan.

Types of Winter Injury

The following forms of winter injury which have been referred to in the preceding notes are given special attention hereunder.

(1) Killing back of branches.

This type was found on every tree except the hardy varieties of Polish and Russian origin. In some cases the large branches were killed outright, but usually the injury was confined to small branches, and the degree of injury varied from slight to very severe killing. Branches so injured were attacked by fungus diseases and some were beginning to decay and fall off when examined in October. Killing back of the branches was also noted on one excellent heartnut at Scotland, Ontario. This tree was subjected to -30 degrees F. but was less severely injured than many of the English walnuts noted above, and when examined in September showed a vigorous new growth throughout most of the top. There were also several vigorous seedlings from this tree growing near by which were only slightly injured in the bark or which were uninjured. It was interesting to observe that the seedlings of the old heartnut tree that were apparently of hybrid origin were not injured in the least and bore good crops of nuts this year, but the seedlings that were pure heartnuts were injured slightly. This point suggests the desirability of crossing the finest heartnuts with the best butternuts to get a combination of the hardiness of the butternut with the good qualities of the heartnut.

Bark Killing

Bark injury is often found on fruit trees following a severe winter and is occasionally found on nut trees. It may be due to bark splitting or to desiccation or both. In severe cases of bark splitting the bark splits vertically and laterally from the ground up for several feet, but in milder cases the bark is only split away for a short distance. Where the bark is loosened for some distance around the tree or vertically it dies shortly thereafter, but where only a small amount of splitting occurs, the tree may recover if given attention. In such cases the bark should be cut back to the living tissue and all particles of dead or injured bark scraped off. The exposed area should then be coated with a good tree paint or asphaltic emulsion.

The severest case of bark splitting observed was on a vigorous young heartnut seedling at Guelph, Ontario. On this tree the bark was completely split away entirely around the trunk from the ground up for several feet and the injury was so great that the tree died early in the summer. Within a short distance of this tree was another tree of the same origin that was quite uninjured, but this tree, however, was a hybrid between the butternut and the heartnut. On this hardy tree there was a heavy crop of nuts that were intermediate in form between the heartnut and the butternut, this indicating its hybrid origin. Practically all of these hybrids escaped injury even though the temperature was -30 degrees F.

Bark injury was also noticed at the Kellogg Farm on several black walnut trees that had been grafted in the nursery and which were planted in 1932 and 1933. On these trees the scion variety was uninjured but the bark on the stock was more or less affected from the ground up to the point of union. All trees thus affected came out into leaf, but shortly afterward the leaves withered and the top died.

Bark injury from splitting or desiccation was more prevalent on young vigorous growing trees, and on older trees that had been stimulated into a strong growth by fertilizers or late cultivation.

Suggested Means of Control

Since it is impossible to control temperatures and precipitation, it is perhaps a vain hope to expect complete immunity from winter injury to the English walnut. It is possible, however, to lessen the degree of injury by certain measures of precaution. These are as follows:

(1) Plant only the hardiest varieties.

The past winter showed very clearly that the commercial varieties of English walnut or seedlings as grown in this state are not hardy enough to endure the severe cold that periodically occurs in Michigan. This limits the choice of varieties to those from central Europe or north China where rigorous climatic conditions prevail. As already pointed out, the varieties that endured the past winter were from the Carpathian region in Poland or western Russia and north China. These varieties have not been widely distributed in this state and it may be found that even these will have a limited range in Michigan. Their behavior, however, shows that they are somewhat hardier than varieties from western Europe or England. Unfortunately the supply of trees of these apparently hardy kinds is limited and it will take some time to work up a stock of the best strains. In the meantime, those who desire to plant the English walnut had better wait until a supply of the hardier kind is available or plant some other hardy species such as the black walnut.

(2) Thoroughly drain all soils intended for nut trees. Well drained soils favor good root development and seem to lessen late growth, thus reducing to a slight extent at least the severe killing back that is noticeable on such growth.

(3) Use nitrogenous fertilizers in moderation.

Fertilizers rich in nitrogen may stimulate the late growth and predispose the tree to killing back.

(4) Do not cultivate the soil around nut trees late in the summer.

Late cultivation stimulates late growth and prevents the trees from properly ripening their buds and wood. This late growth invariably suffers more severely from winter cold than growth that is well matured.