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Selecting a favorable location for nut trees is very important. They should never be planted at the bottom of a gulch or valley because, in such places, frost pockets may occur which will interfere with both blossoming in the spring and ripening of nuts in the fall. Nut trees grow best near the summit of a hill. Although such soils are difficult to plant in, stony soil or soil overlaid with limestone results in good growth. Shallow surface soil, underlaid with heavy clay, will usually slow down the growth of a young tree so that it remains dwarfed for many years. It is more satisfactory to have at least three feet of soil before clay is reached. If the soil is light and sandy, it will be improved by adding black dirt immediately around the roots of each tree.
As most nut trees ultimately grow to be very large, they should be planted at least forty feet apart. The hole dug to receive each tree should be wide and deep enough to accommodate the roots without bending or twisting them. If the excavated soil is of poor quality, it should be discarded, and good, rich soil brought in for setting the tree. Trees should not be planted too deeply. The collar of a tree, which is a discoloration of its trunk resulting from contact with the ground, indicates how much of the tree was previously underground. Although it is a good idea to plant so that this collar is a little lower than the surface to allow access to extra moisture, the actual planting depth should be about as it was previously in the nursery. All broken or damaged parts on the roots should be trimmed smoothly with pruning shears. Such clean cuts will send out new rootlets to replace the lost ones. After a tree has been set into the hole made for it, the soil, which should be thoroughly mixed with a quart of bone meal to increase its fertility, is replaced a little at a time. It must be packed very solidly about the roots with a rounded tamping stick to avoid leaving air pockets. I find it advisable to retamp the earth about each tree two or three times during the first year's growing season, to insure intimate contact between soil and roots.
Planting should be delayed if the soil is very wet. Trees will stay in good condition for several days, if the burlap sacks are kept moistened. Wet, soggy soil is certain to shrink away from the roots and leave air pockets which will, in time, kill the trees. If trees are transplanted during a very dry season, they should be thoroughly watered. To do this, remove several shovelfuls of dirt from the ground about a foot from the tree, being careful not to cut any roots. Fill this hole with water and after the water has seeped away, fill it two more times. The tree should receive about five gallons of water. Sprinkling with a hose does not suffice. If dry weather continues, each tree should be watered in this way every week.
Nurserymen in the future will have to deal with this transplanting problem in a different way than the old time nurserymen who handles fruit trees. A suggested way to improve the root system and at the same time make it easy to lift the tree with a ball of dirt, similar to the way an evergreen is transplanted, is to prepare a pocket of special transplanting soil previous to the lining out (which is the term used by nurserymen in setting out seedlings preparatory to grafting them in nursery rows). A suggested balanced soil for making the method practical is to use 1/2 by volume of peat moss; the other half should be rich, black sandy loam with very little clay mixture in it. In other words, each nut tree should be allowed about a bushel of soil for its development, 1/2 bushel to be peat moss, the other half bushel to be represented by rich black loam. This mixture will encourage many fibrous roots to develop and when the tree is dug, approximately all of this bushel of soil will be retained around the roots. Having such a high proportion of peat moss makes it lighter than ordinary ground; such a ball and the tree will weigh approximately from 100 to 125 pounds which can be shipped by freight at a low rate and is well worth the extra price that nurserymen must ask for a specimen of this kind. Such trees have really never been unplanted and for this reason do not suffer the shock which is inevitable in the usual transplanting process. Although pre-planted trees are more expensive to buy and to transport, their improved chances of living make them worth the price. The above recommendation is especially applicable to young grafted hickory trees since they are among the most difficult trees to transplant satisfactorily. The English walnut (Persian), black walnut, butternut and especially the hickory are improved by the use of a handful of ground lime mixed with the soil in preparing these pockets which will later constitute the ball surrounding the roots of the tree to be transplanted.
There is a tendency in grafted trees to produce sprouts below the graft. Unless these are rubbed off, the grafted portion will become discouraged and the tree will revert to a seedling variety. Filberts should never be allowed more than two or three stems, or trunks, while one is more preferable. If they are allowed to have more, they will produce a rank growth of wood but only a few, if any, nuts. I stress, by repeating, that trees should not be planted too deeply and that great care must be taken to eliminate air pockets. Extra effort and nursing of transplanted trees during the first season will be repaid by their successful development and growth.
It is a wise precaution to place a protective screen around the trunk of each tree to prevent rodents from attacking it. Mice gnaw off the bark near the ground, sometimes girdling a tree and so killing it. Rabbits chew off branches and they, too, may girdle the upper part of a tree. Rabbits are very fond of pecan and hickory bark. In some places, it may be necessary to encircle each pecan and hickory tree with a three or four-foot rabbit fence until the tree is large enough to lose its appeal to these nuisances.
Compared with the number of insects which infest fruit trees, very few attack nut trees. One of those which does is the walnut-leaf caterpillar. These appear as a closely congregated group of small worms which feed on the leaves of black walnut and hickory trees during the latter half of the summer season. Very often they are all to be found on a single leaf, which should be picked from the tree and crushed underfoot. A simple spray of lead arsenate of the strength recommended by companies selling spray material, will effectively rid trees of these pests. Another insect often found in a nut orchard is the oak tree girdler, which also is active in the latter part of the summer. It often causes limbs as large as an inch in diameter to be cut through and to fall to the ground. By removing such freshly girdled branches and cutting into the hollow made by the larva, it is possible to find the live worm and destroy it. A good way to combat this pest is to keep each tree pruned of all dead branches and to burn all broken and dead wood each fall. While some nut trees are subject to other insects, the two described here are the most frequently found. Fortunately, they are easily controlled if a watch is kept for them.
Chapter 14
WINTER PROTECTION OF GRAFTS AND SEEDLINGS
It is not enough to make a successful graft and to watch it carefully during the growing season, picking all sprouts off the stock, spraying it so that insects will not chew the tender leaves and bark, bracing it against windstorms and perching birds. Each graft must also be protected from winter injury. For many years I have studied and experimented to find a successful way of achieving such protection. To enumerate my many experiments, from simple to far-fetched, would be to write another book quite as long as this one. My conclusion, now, is that there is little one can do to assist nature in the process of acclimatizing grafted plants and seedlings.
I have repeatedly noticed that the place where most damage is done by the cold is at the union between stock and graft. For example, I observed this on the European walnuts, imported from Poland, grafted to Minnesota black walnut stocks. Although both the buds and the wood of the top remained fresh and green, the unions suffered severe, and sometimes total winter injury. In grafts where the latter occurred, the dead cells soon caused the wood to ferment and sour. Occasionally, a small group of healthy cells succeeded in re-establishing circulation with the unharmed, grafted top and the graft, continuing its growth, would eventually overcome the injury it had suffered. I have seen this occur with grafts of English walnut, apricot and pecan.
A blackbird's nest in the crotch of a small tree suggested to me the most satisfactory guard I have yet found against this greatest of dangers to all exotic, grafted varieties of nut trees. The nest, which enclosed over half of the graft union, was partly composed of woolen fibers which its builder had gathered from barbed-wire fences that sheep had brushed against. On the exposed portion of the graft union, discoloration indicated injury and dead cells, but on that part covered by the nest, all the cells were alive and green. I have improved on the bird's nest by wrapping a large wad of wool loosely around each graft union. The value of wool is that it will not collect moisture and so start fermentation. It allows the cells to breathe, yet protects the union from the shock of temperature extremes. Birds will inevitably steal some of the strands of wool but this activity in and about the trees means a decrease in injuries from insects—a worthwhile exchange.
When an unusually large swelling at the graft union appears, it is certain that the plant needs protection such as I have described. Such swellings result from a too-rapid multiplication of cells, a condition which leaves the union weak and susceptible to injury. Although a union is never entirely safe, even after many seasons of growth, each year adds to the safety factor by the development of rough, cork-like bark. I suggest the use of a woolen guard for several winters, by which time this outer bark should be able to do its protective work alone.
A successful but rather expensive method of winter protection, both to the graft itself and its union with its host, is to enclose the entire tree with a box-like structure consisting of four corrugated aluminum roofing sheets set up on their ends and countersunk into the ground about six inches. The purpose of countersinking these below the ground surface is two-fold: it stiffens and braces the structure and prevents the intrusion of mice and other rodents, which may also appreciate both the shelter and possible food supply contained therein. By fastening these sheets together with a stout wire you can depend on the structure to stand up against wind and snow pressures. Fill the entire inside with forest leaves, oak leaves preferred, as their insulating quality is the best and they are slow to rot and ferment.
When working with semi-hardy plants in a cold climate, avoid fertilizing and cultivating the ground after the first of August. Doing so stimulates late growth and such growth is very likely to be badly injured during the winter months. If fertilizer is used, it should be early in the spring, as soon as the ground is free from frost. Trees which persist in growing late into the fall are more subject to winter injury. Protective measures to avoid their doing so by inducing an earlier dormancy, include keeping the soil around them dry and exposing, somewhat, the roots near the trunk of each tree.
My last word of advice in raising what might be termed semi-hardy trees, is to grow them in sod, the ordinary quack grass, June grass, bluegrass or other natural grass sods which can be found on your planting site. Although this will probably hold back your tree development for a few years, until the roots are thoroughly established in the deeper soil beneath the sod roots, it is surprising how many species of trees will thrive in sod and perish on open cultivated ground. I can give no better example of this than relating a circumstance which bears this out in a most convincing way. In 1941 I purchased about 250 filbert seedlings from Samuel Graham of Ithaca, New York. These were planted out on a field site and practically all of the plants made good growth the first year. They were thoroughly cultivated. The next year a second batch of plants of a like amount were purchased from the same man and of the same kind of seedlings. Mr. Graham told me that these were seedling trees from Jones hybrid seeds which he had growing in his orchard. These plants were put on heavy sod ground; all plants were protected by screens, but the plants on the sod ground were subject to a very wet season and it was necessary to build up the soil around some of the plants in order to save them from being drowned out. Today about 45 plants are living on the sod culture and two or three barely alive exist in the open field culture. Although the plants remaining alive on the sod culture plot are almost pure filbert strain they are therefore very subject to the common hazel blight. Some have grown into bushes 10 feet high which later were hit by blight and have been reduced to small bushes. Others are producing good filbert-type nuts and are somewhat blight resistant, but the main fact to remember is that about 1/4 of the plants on sod culture lived, whereas not over 2% are alive of the open field culture plants. The distance between these plantings is approximately 1/8 of a mile. In addition to being placed in sod these filberts which have survived are sheltered by rows of evergreen trees both on the south and on the north side which may be construed as of some assistance but is not altogether the reason for the tremendous difference between the winter protection value of sod and open field culture. This is not the only example that I could cite but is one of the most outstanding ones which has come to my attention. Sod culture is now being recommended to fruit orchardists in this part of the country and in my own experience, I can highly recommend it for apples, plums, pears, mulberries and nut trees.
Chapter 15
TREE STORAGE
If it is necessary to store trees through the winter months, one of several procedures may be followed. If the trees are quite small, their tops may be dipped in melted paraffin or beeswax, not hot enough to injure the buds. If the trees are too large for this to be practical, wax may be painted on with a brush. Roots should be protected by heeling them in dirt.
An unheated cellar with a dirt floor is a very satisfactory place for storing trees. Select a corner of the cellar far from any source of heat or temperature change. Place the trees so that the roots are pointing toward the basement wall. Cover the roots to a depth of six inches with either sand or sandy loam, packing the soil firmly to eliminate air pockets. Lastly, cover the trees completely with burlap sacks. Once every two weeks, the earth around the roots should be watered. Trees maintained in this way are conveniently ready to plant when the ground thaws out in the spring.
Another and better method of storing trees is to plant them outside in a trench, preferably on the north side of a building, having first waxed them as described above. One side of the trench should slope so that the trees will lie in an oblique position with their branches touching the ground. The roots of these trees should be covered with dirt, then more trees set alongside them, until all have been planted and the earth made firm about their roots. Trees will usually suffer no damage during such winter storage if their roots have been properly packed in sand or sandy loam. Six or more cans, each containing a little poisoned grain, should be set among the branches. If these cans are laid on their sides, rodents will have easier access to the poison. The branches of the trees should then be well covered with straw or hay, with heavy boards laid on top to keep it from blowing away. If trees are received for planting after the ground has frozen, all that is necessary is to build a log fire on the side where they are to be heeled in. This will thaw out the soil enough so that a trench can be made to accommodate them.
Chapter 16
SUGGESTIONS ON GRAFTING METHODS
Grafting, including budding, may be defined as inserting a piece of wood which carries buds of a desired variety, on a root stock sufficiently compatible to accept it, for the purpose of propagation. Methods vary, each nurseryman having one or more which he prefers, but the principle is always the same.
Scionwood may be cut the fall before grafting is to be done, after the growing season has ended, but some prefer to cut the scions in early spring. This means that the scions must be stored until time to graft, and correct storage is so important that nurserymen make elaborate provision for it. I have found that keeping scions underground in a Harrington graft storage box is the safest method. An illustration of this box is given, with directions for its construction and location. A small quantity of scions may be kept in an icebox (not a mechanical refrigerator), by cutting them into convenient lengths of one or two feet, dipping them in melted beeswax, wrapping them in tar or asphalt paper and placing them close to the ice. They will remain in good condition for several months if there is always a good supply of ice. Care must be taken in dipping the scions in melted wax, for if the wax is too hot it will injure the buds. It should never become so hot that it smokes. I find it advisable to keep an unmelted piece of wax in the liquid wax to hold the temperature down.
Another method of storing scions, after they have been dipped in beeswax, is to place them on the earth of a cellar floor and cover them with a few burlap sacks. They should never be allowed to become wet or they will start to mold. If they are to be stored in this way, a watch must be kept for mice which will molest them and destroy them if they have an opportunity.
Although bud wood may be stored in any of the three ways mentioned, it should not be waxed. Because of this, it is more likely to deteriorate. It must be examined frequently and if mold is found, the wood should be dipped in a Bordeaux solution. After drying, it may be placed in storage again. It is a good plan to wrap bud wood in tar or asphalt paper when storing it. However, I have found that the best storage conditions for all scionwood that I have yet discovered is in the use of peat moss. Peat moss must be on the distinctly acid side in order to perform the function of storing scionwood. Most peat moss is generally acid; however the simple litmus paper test with which every high school pupil is familiar, can be made. Having acquired good acid peat moss, dampen a sufficient quantity to pack the scions in to give them liberal protection. Do not make the bundles of scionwood too large, from 10 to 20 scions in a bundle is better than a large number and much easier to handle. The moss should be prepared exactly the same as advised in storing chestnuts (see chapter for storing seeds). In this case it is not necessary to wax the scions at all. The moss should be applied by sifting it into the open spaces between the scions and a larger wad at the base of the cuttings, not at the terminal or bud ends as these would be better left unpacked. The package is now rolled into a cylinder, using tar paper or asphalt treated paper, and both ends left open. Do not use ordinary paper or wax paper as it will turn moldy. Cylinders of tar paper containing the packed scions should be placed in a damp room like a cellar with a dirt floor which is cold enough to keep potatoes and other roots in good condition throughout the winter. If the cellar is not a good storage cellar for roots and herbs it will not be good enough for the scionwood as it will be too warm generally. Neither should they be frozen solid, therefore if a good root cellar is not obtainable then these should be put in the Harrington graft box already described or placed under the sawdust in an icehouse and close to the ice. An old-fashioned ice refrigerator will also make a good storage bin, placing them close to the ice at all times.
Selection of good scionwood and bud wood, a very important matter, is made according to definite standards. Some plants graft better if wood is used that has two seasons' growth, but, in general, wood of the current season's growth is used. It must have reached its maximum possible maturity before it is cut. Also, some attention should be paid to the vigor of the growth which it has made during the season. For instance, in choosing between wood which has made only two or three inches' growth and that which has made a foot or more of growth, both being equally sound and mature, the more vigorous should be chosen. Attention should be paid to the development of the buds, which should be plump and never immature.
It is advisable to label scions before they are stored to avoid the confusion that will result if they are mixed. I find that the best method of doing this is to get a sheet of zinc, from 20 to 30 gauge thick, and cut it into strips one inch wide by one and three-quarters inches long. I bore a small hole in one corner of each tag, through which I thread 18-gauge copper wire, doubled and with the bottom loop folded over (see page 40). In preparing these tags, it is important to remember that both wires must pass through the hole in the metal tag, otherwise, the slight movement due to winds will cause the metal to wear through. Two wires prevent this action indefinitely. Since a small wire cuts through a zinc tag in one or two years, heavy wire must be used. Wire such as I have indicated is satisfactory. I print the necessary information on each tag with a small, steel awl, and such labels are still legible after twenty-five years. Copper, brass or aluminum would also make good tags, but these metals are more expensive. Of course, these tags may be used for small trees as well as grafts and scionwood and it is always well to do a good job of labeling all work, since many errors may result from disregard to this important detail.
In the north, the time to graft nut trees is when the cambium layer of the host, or stock, is active, which is usually during the entire month of May. This cambium layer consists of those cells lying just inside of the outer bark, between it and the woody part of the tree. When these cells are active, the inner side of the bark feels slippery and a jelly-like substance can be scraped from it. Although this is the state in which the stock should be for grafting, the condition of the scions should be almost the opposite, rather dry and showing no signs of cambium activity. The bark should cling firmly to the woody part of the scions, whereas the bark of the stock should slip off readily. Another good and fairly satisfactory rule is never to graft the stocks of nut trees until after the young leaves appear.
In grafting young nursery trees not more than an inch in diameter, the whole tree is cut off at any distance from the ground convenient to the nurseryman. Sometimes they are cut within a few inches of the ground, sometimes two or three feet. In my work, I like to keep the scions as high above the ground as I can. When the top of a stock is cut off, there is a great deal of sap pressure and the tree bleeds. It is a poor policy to attempt grafting while this is happening. Rather, one should cut the tops off, then wait for several days before inserting any grafts. Tools must be kept very sharp. A good grafting knife is sharpened on one side only, so that the blade is flat along the side which lies next to the cut made on the scion when it is trimmed. If unaccustomed to handling a knife, one can obtain more accurate results by using a small plane. I do this by holding the scion firmly in my right hand and pulling it toward me, against the cutting edge of the plane which is held in the left hand. Illustrations show how this is done.
The only disadvantage in using a plane is that one must exchange it for a knife to make the receiving cut in the stock before inserting the graft. This necessitates exposing the graft to the air for a longer time than does using a single instrument.
Spring budding is done during the same period as grafting. Bud wood is usually much larger in diameter than scionwood, for it is easier to remove buds from big branches than from wood only one-quarter inch in diameter. When budding is to be done, take along only enough wood for half a day's work, leaving the rest safely stored. A piece of wood having a bud is prepared as shown in the illustrations "A" and "B" (next page). A T-shaped slot is made in the stock to receive the bud, a process called "shield budding." This is tied in place with either string, raffia or gummed tape, as shown in "C" and "D" (next page). The bud must be free to grow, and although it may be covered completely with wax, no part of the binding material should be close to it. Since it is not necessary to cut off all the tree in budding, enough of it may remain above the bud to brace the shoot that develops. Later, it may be necessary to cut back the tree to the bud so that a callus will form and cause the wound to heal properly.
Best results are obtained when a graft union is coated with melted beeswax. Another and cheaper wax may be made by combining four parts of rosin, one part of beeswax and one-sixteenth part of raw linseed oil. To this is sometimes added a little lampblack to color the mixture so that it can be seen on the graft. Again, care must be taken to prevent injuring the cells with wax that is too hot.
I have used many kinds of tying materials, but the one which gives me best results is gummed tape, which preparation I describe in another chapter. By wrapping it in spirals around a graft union, I have a material which holds the graft in place and at the same time excludes air. The rubber also seems to encourage the formation of that tissue which unites the stock and scion. In addition to tape, melted wax should be brushed into those crevices and cracks which always occur in making a graft.
It is usually advisable, although not necessary, to shade new grafts. To do this, cover them with light-colored or white paper sacks. Never use glassine alone for it causes the grafts to overheat and so destroys them. Whatever tying material is used, either to fasten on these bags or to support the grafts, it should be inspected at intervals during the summer, as it may constrict the graft or stock and injure or cut off the cambium.
After a scion begins to grow, it must be firmly braced against the force of the wind, for a heavy gale can rip out grafts made years before. Laths make good braces for growing shoots. They may be attached to the main branch by stout waterproof twine such as binder twine, and the growing graft tied with soft muslin strips to the lath. As the graft grows more muslin strips should be used to keep the excessive growth anchored to the lath. Grafts will often make three or more feet in growth in one season.
It is important to remember that sprouts or buds which start from the stock must be rubbed off. If they are allowed to flourish, they may prevent the scion from growing. When working over a tree several inches in diameter, it becomes an art to keep the tree stock satisfied, yet to encourage the growth of the scions. In large trees, a few sprouts must grow to nourish the root system, but this is not necessary if the stock is one inch, or less, in diameter.
Chapter 17
GRAFTING TAPE VERSUS RAFFIA
It is necessary that a person who is grafting trees and developing hybrids experiment not only with the plants he is interested in, but also with the equipment and materials he uses. For more than twelve years, I used raffia to tie the grafts I made, becoming more annoyed and irritated with its limitations each year. Finally, I began trying other materials, until I found one which I think is very satisfactory. This is a rubberized grafting tape.
At my nursery, we make our own tape. We buy pure rubber gum, known as Lotol NC-356, from the Naugatuck Chemical Company, at a cost of $7.50 for five gallons, F.O.B. their factory. With this, we use unbleached muslin of an 80 x 80 mesh, or finer. As the muslin is usually a yard wide, we fold it and take it to a printing firm, where, for a small charge, it is cut into both one-half and three-quarter inch strips by being fed through a paper-cutting machine. We use the wider strips for heavy work on large trees which have three to five-inch stubs; the narrower strips we use in the nursery, grafting young seedlings.
First, pour about a gallon of the rubber compound into a twelve or sixteen-quart pail having a smooth, rolled edge. Next, separate a dozen or so of the strips of muslin. Then, set out a pair of rails on which to dry the tape after it has been dipped. I make these rails by using two 1" x 2" boards about twelve feet in length, nailed together at the ends with boards two feet long. This frame, resting on carpenter's horses or benches, makes a good drying rack.
Holding a piece of tape by one end, submerge it in the rubber solution, forcing it down with a spatula or knife. Swishing it around or moving it up and down several times helps to fill the pores with rubber. Drag it from the solution by pulling it sharply over the rolled edge of the pail, using the spatula on the upper side of the strip to scrape off superfluous rubber. A little practice soon enables one to judge the amount of rubber needed on the tape. There should not be so much that it drips off. Hang the tape on the rack so that the ends are attached to the rails, the tape sagging slightly in the center. Space the pieces of tape so that they do not touch, for, if they do, they will be very difficult to separate later. After they have dried for twenty-four hours, wind the tape on pieces of cardboard about one foot square, being careful not to overlap the tape. The tape is now ready for field-work.
I want to mention some of the advantages I have found in using this rubberized tape rather than raffia. The tape is uniform throughout and is stronger than raffia. It does not fly around and frequently get tangled as the latter does. There is no necessity for keeping it slightly damp to be usable. It may easily be torn off at any convenient length or it may be cut without injuring the edge of the grafting knife. A last advantage is that it is self-sealing since it overlaps on itself slightly when wound around a graft union. Because of this, there is no necessity for painting the finished graft with melted wax as is absolutely vital when using raffia. Personally, I use wax in addition to the tape for I feel that it is probably safer with that extra protection. Also it gives me an opportunity to wax over the tip end of the scion when it is devoid of a terminal bud.
The only disadvantage in using tape is its cost which, I must admit, is very much higher than that of raffia. But if, by using tape, twice as many grafts can be made each day, and if the resulting takes are 50% better, as they have been in my experience, then the cost is justified and raffia is actually the more expensive to use.
Chapter 18
EFFECTS OF GRAFTING ON UNLIKE STOCKS
It is unquestionably a great shock to a tree when 90% of its top is cut off. If it is healthy and vigorous, the root system will try to recover, using every means possible to do so. If a new top is grafted to it, the stock must either accept and nourish that foreign and sometimes incompatible new part, or give up its struggle for life. Nature and the tree stock usually accept the challenge and the graft begins to grow. In an attempt to continue with its own identity, the stock will bring into activity adventitious buds. These are tiny microscopic buds imbedded in the bark of a tree that are not apparent to the eye but are nature's protection against destruction of the individual plant. But these must be removed by the horticulturist to insure proper nourishment of the grafts.
Because the root system is striving hard to live, and because it is usually the stronger, it may force the top to accept certain of its characteristics. Occasionally, it may assume some qualities of the original top. Such cooperation is necessary if either is to survive. First of all, the grafted scions must accept the vital quality of climatic hardiness, a powerful factor developed through ages spent in a certain climate. To hasten the acclimatization of a tender variety, I cut scionwood from such unions early in the winter, storing it until spring. When these scions are grafted on new root systems, I find that they are much more readily accepted than the first grafts were. The following season, I allow the grafts of this later union to go through their first winter of exposure. Early each spring I continue to cut scions from the most recent unions and graft them to new root systems, so hastening and setting the factor of hardiness through frequent asexual propagation.
Because my observations of the effects of scion on root and vice versa, have not extended over a sufficient period of time, I think it is possible that the changes I have seen may be only transient. In any case, I do know that the phenomenon occurs, for I have seen many examples of it.
One instance in which the stock was apparently affecting the scions, occurred in the case of several varieties of black walnuts which had been grafted on wild butternut stock over a period of sixteen years. The walnut top flourished but tended to outgrow the butternut, so that the caliber of the walnut was greater than that of the stock a few inches below the graft union. I also noticed that, although the graft began to bear about as early as black walnuts do when they are grafted on their own species, the nuts did not mature at all during the first few years of bearing. In 1938, after a favorable season, I found mature nuts on one variety, the Thomas. These nuts varied in size more than they do when grafted on black walnut. The most surprising thing about them, though, was that they did not have the characteristic black walnut flavor. When properly dried and cured, they could have passed as an entirely different nut since they tasted like neither the black walnut, the butternut nor the Persian walnut.
The overgrowth of the Ohio black walnut, grafted on butternut, was even more apparent than that of the Thomas. These nuts were, as I have said, immature the first few years they appeared and they, too, lacked the usual black walnut flavor. In their case, however, the most striking change was in the shape and structure of their shells which were elongated like butternuts, with corrugations typical of those found on butternuts and nearly as deep and sharp. (See Illustration in Chapter 1, Page 5.)
In 1937, I made experimental graftings on native black walnut stocks of the Weschcke No. 4 butternut, a variety I found to be superior to hundreds of other native trees tested. The grafts grew luxuriantly and in 1940, produced about two pounds of nuts. These nuts were approximately 30% larger than those on the parent tree. They cracked well and the kernels were similar to those from the parent tree. They definitely distinguished themselves, however, by being a free-hulling nut, which is not true of the mother tree nor of most butternuts. Soon after the nuts had dropped to the ground and were still green, they were hulled and their hulls peeled off like those of the Persian walnut, leaving the nuts clean and free from remnants. Apparently this phenomenon was a transient one since later crops did not display this free-hulling feature.
I have mentioned, elsewhere, the seedling apricot which came into bearing in St. Paul, and how I obtained grafts before it died during a very cold winter. I have grafted scions of this apricot on both hybrid and wild plum stocks repeatedly and this apricot now exhibits a material gain in hardiness. It overgrows the plum stock, but this does not seem to inhibit its bearing, the fruit growing to greater size than that of the mother tree.
These are some of the instances in which I have seen stock exert a definite, and, mainly a beneficial influence on its grafted top. It may easily be that these are only of a temporary nature and until I have seen them maintained for many more years, I must consider them to be transient effects.
Chapter 19
DISTINGUISHING CHARACTERISTICS OF SCIONS
Loss of identification markings from my grafted trees has, on occasion, caused me much confusion. There was one time when I had from six to ten varieties of hickories and their hybrids grafted on wild bitternut hickory stocks, totally lacking in identification. Although this disconcerted me considerably, I knew of nothing I could do except to wait for the grafts to bear nuts and determine the varieties from these. As I continued my experimental grafting, I made sure that the tags I used were not only indestructible, but also secured to the grafts in such a way that the action of the wind could not wear them out nor cause them to drop off.
Not long after this had happened, I received from Dr. Deming a shipment of about twenty varieties of hickory scions. While I was preparing this material for grafting, I noticed that each variety could be readily distinguished by its appearance in general and, specifically, by differences in its leaf scars. I also noticed markings on the bark, particularly the stomata, which differed with each variety. Color and stripes added further differentiation. Although I also found variations in the size and shape of the buds, I later discovered that these do not always remain constant within a variety, but depend somewhat on each season's growth. For instance, a second growth sometimes develops during a favorable season with a large number of lateral buds growing out of it like spines.
It seemed to me that if scions could be maintained in an approximately fresh state, they would furnish a key by which any variety of graft could be determined as easily as it could by its nuts. I therefore set myself to preserve scionwood in its fresh state. First, I cut five-inch pieces of plump, healthy wood, each piece having a terminal bud. I placed these buds downward in large test tubes which I then filled with pure, strained honey. Such models did very well for a time, but after about a year, the honey crystallized and of course the scions were no longer visible. I emptied the tubes and washed them, cleaned the scions in warm water, replaced them and refilled the tubes with pure glycerine. I submerged a thin, zinc tag, stencilled with the varietal name and bent to conform with the contour of the tube, inside of each one as a name plate which could not easily be lost or removed. I also labeled each cork with the name of the variety enclosed so that any one of them could be located when looking down at a nest of tubes in a vertical position.
In order to display these preserved specimens at illustrated lectures, I had a rack made of redwood, of a size to hold twenty tubes. The tubes could easily be taken from the rack for closer observation by members of an audience. I find this to be an interesting adjunct to various nut culture exhibits I make in trying to promote nut culture education.
Since I was able to identify my unlabeled, hickory grafts by means of this catalogue of submerged scions, I consider it of great practical worth. At the present time, I have about 50 hickory specimens, a good catalogue, although not a complete one. I see no reason why the same thing could not be done with black walnut or any other kind of nut scions.
Chapter 20
HYBRIDIZING
Working with nature to develop new varieties of trees is fascinating although it requires infinite patience and study combined with skill and concentration. A person without experience may taste of this pleasure, however, by trying his hand at cross-pollination, and there is no end to the number of hybrids possible.
In attempting to make crosses, one must necessarily understand the botanical relationship between the trees to be crossed. Trees of the same species cross readily in almost all cases; trees of the same genus are not as easily crossed; trees belonging only to the same family are usually difficult to cross. It is generally assumed that trees not in the same family are impossible to hybridize. The plum serves as a practical example of this. The American wild plum crosses readily with almost any other plum and particularly well with the Japanese plum. These crosses have resulted in such phenomenal fruit as the Underwood plum, a cross made between species. If a cross were made between a chestnut and a walnut, it would be between members of different families. I recommend to anyone who is attempting to cross-pollinate for the first time, that he limit his work to crosses made within species. His chances of success will be greater and such success added to the experience he is acquiring, will give him the background needed for more difficult hybridizing.
Crosses made between filberts and hazels usually produce great changes in the resulting fruit. J. F. Jones won considerable horticultural fame from crosses he made between the wild American hazel known as the Rush hazel, and such varieties of the European filbert as the Italian Red and Daviana. Hazel and filbert cross readily and the resulting seedlings will usually bear after only three or four years. For both these reasons, they are good material for a beginner to work with. If the wild hazel is to be used as the female, or mother, of the cross, it is necessary to pick off all the male blossoms, or staminate blooms. This should be done long before they begin to expand. The pistillate, or female blossoms, should be enclosed in bags, about six of the three-pound, common kraft bags should be enough. These are slipped over those branches which bear female blossoms and are tied around a heavy packing of absorbent cotton, which has been wound around the branch at approximately the place where the opening of the bag will be. In fastening the mouth of the bag around the cotton, I find that No. 18 copper wire, wrapped several times around and the ends twisted together, is more satisfactory than string. This makes a pollen-tight house for the pistillate blossoms but not one so air-tight as to cause any damage to either the plant or blossoms.
In order to have pollen available at the proper time, it is necessary to cut a few filbert branches which bear staminate blooms and store them in a dark, cold place to prevent the pollen from ripening too soon. I recommend keeping such branches in dampened sphagnum moss until it is time for the pollen to ripen, or if a cold cellar is available, burying the cut ends of large branches carrying male catkins one foot deep in clean, moist sand. When the pollen is wanted, the branches should be placed in a container of water and set near a window where sunlight will reach them. Usually, after one day of exposure to bright sunlight, the staminate blooms will expand and begin to shed their pollen. The pollen may easily be collected by allowing an extended catkin to droop inside a vial or test tube and then, as the catkin rests against its inner wall, tapping the outside of the tube sharply with a pencil to jar the pollen grains loose. A separate test tube must be used for each variety of pollen to be experimented with. By following this procedure for several days with all the staminate blooms that have been gathered, the experimenter should have enough pollen for work on a small scale. The test tubes containing this pollen should never be stoppered with corks, but with plugs of absorbent cotton, which will allow the passage of air. Pollen may be stored in this manner for several days, possibly as long as two weeks, if it is kept dry. By a close observation of the blooming period of the wild hazels, one is able to determine the best time for placing the filbert pollen on the pistillate blossoms. No attempt should be made to do so until the male catkins of the wild hazel species are so entirely exhausted that no amount of shaking will release any grains of pollen. When this condition exists, it is time to move the stored filbert branches to strong sunlight. A quiet day should be chosen to pollinize the hazels for two reasons. If there is a wind, it will blow away the pollen and so make the work more difficult. A wind will also increase the danger of the hazels being fertilized by native hazel pollen which may still be circulating in the air and which the flowers may prefer to filbert pollen.
When good conditions are present, then, the hybridizer proceeds to his work. A brush with which to transfer pollen from the vial to the pistillate blossoms is made by wrapping a little absorbent cotton around the end of a match. The paper bag is removed from around a group of hazel blossoms, a small amount of pollen is dabbed on each blossom and the bag is immediately replaced, to remain on for two more weeks. When the bags are finally taken off, the branches should be marked to indicate that the nuts will be hybrids. Before receiving pollen, each pistillate blossom has, emerging from its bud tip, a few delicate red or pink spikes which are sticky enough to make pollen adhere to them. Within a few days after receiving pollen, these spikes may dry up and turn black, a fair indication that the pollen has been effective. If the pollen does not take hold, the spikes of the staminate blooms are sure to continue pink for a long time. I have seen them in the middle of the summer, still blooming and waiting for pollen which would let them continue on their cycle. This ability of hazel flowers to remain receptive for a long period allows the nut-culturist ample time to accomplish his work. It is not so true with all members of the nut tree group, some, such as the English walnuts, being receptive for such a short period that only by very frequent examination and many applications of pollen can one be sure of making a cross.
Early in the fall, the hybrid nuts should be enclosed in a wire screen to prevent mice and squirrels from taking them before they are ripe. Such wire screens may be used in the form of a bag and fastened around each branch. When the husks turn brown and dry, the nuts are ripe, and ready to be gathered and planted. Careful handling of the nuts is advisable to preserve their viability. They should be planted in an outdoor bed which has been fully protected against the invasion of rodents. A screen such as I described for other nut seed is satisfactory for these hybrid nuts but it need not be as large as that. After the nuts have sprouted and the plants have grown for one season, they may be transplanted into a permanent location where they should again be well protected against mice by a trunk screen, and against rabbits by driving a stout stake deep into the ground on the south side of the tree and tying it to the tree. This use of a stake discourages rabbits from cutting off the tree.
There are innumerable other crosses that can be made as well as those between hazels and filberts. It is possible, for example, to cross the English walnut with the black walnut. Many such crosses have been made although none of them is known to have produced superior nuts. Thousands of crosses exist between butternuts and Japanese heartnuts. Many of these are of some worth and are being propagated. Crosses between heartnut and butternut are easily made, following the same procedure used in crossing hazels and filberts, except that larger bags are necessary for covering the female blossoms. Also, these bags should have a small, celluloid window glued into a convenient place, so that the progress of the female blossoms toward maturity can be observed.
When hybridizing walnuts, it is necessary to use a pollen gun instead of removing the bag from around the female blossoms and applying the pollen with a cotton-covered applicator. Such a pollen gun can be made by using a glass vial which does not hold more than an ounce of liquid. An atomizer bulb, attached to a short copper or brass tube soldered into a metal screw-cap, is fitted to the vial. Another small copper or brass tube should also be inserted in the screw-cap close to the first one. The second tube should be bent to a right angle above the stopper and its projecting end filed to a sharp point. Without removing the bag from around the pistillate blossoms, the hybridizer forces the point of the atomizer through the cotton wadding between bag and branch. The pollen in the vial is blown through the tube into the bag in a cloud, covering all the enclosed blossoms. It is advisable to repeat this on several successive days to make certain of reaching the female blossoms during their most receptive period.
Chapter 21
TOXICITY AMONG TREES AND PLANTS
Although quack grass will grow luxuriantly up to the trunks of both black walnut and butternut trees, I know, from things I have seen myself, that the roots of the latter and probably of the former have a deadly effect on members of the evergreen family. I have seen northern white pine and other pines, too, suddenly lose their needles and die when, as large trees, they have been transplanted to the vicinity of butternut trees. To save as many of these transplanted trees as possible, it was necessary for me to sacrifice almost one hundred fine butternut trees by cutting them off close to the ground and pruning all the sprouts that started.
Other instances have also demonstrated to me this deleterious power of butternut trees over evergreens. For years, I watched a struggle between a small butternut tree and a large Mugho pine. Gradually the Mugho pine was succumbing. At last, when the pine had lost over half its branches on the side near the butternut, I decided to take an active part in the fight. I cut off the trunk of the butternut and pruned off all of its sprouts. The butternut surrendered and died. The Mugho pine took new heart, lived and again flourished.
At another time, I transplanted several thousand Montana pines, about thirty or forty of which came within the branch limits of a medium size butternut tree. Within a year, these thirty or more trees had turned brown and were completely dead, while those immediately outside the branch area were dwarfed and not at all thrifty. The trees farther from the butternut were unaffected and grew consistently well. A similar condition, although not to the same degree, developed under a white oak where more Mugho pines were growing. Another instance occurred when a planting of several thousand Colorado blue spruce were lined out and fell within the area affected by two butternut trees. The spruce were all dead within a few months.
Many people have observed the detrimental effect of trees of the walnut family on alfalfa, tomatoes and potatoes, resulting in wilting and dying. It is the root systems of the walnut which are responsible for this damage. Apparently, there is some chemical elaborated near the surface of the roots, and sensitive plants, whose roots come in contact with either roots or ground containing this factor, are injured and sometimes killed by it. One must therefore be very cautious about trusting these trees as protectors of many of the ornamental and garden plants. I am certain, from my own observations, that their influence on evergreens is strongly antagonistic.
On another basis is the association between catalpas and chestnut trees growing adjacent to one another. Constructive symbiosis apparently develops when a young chestnut tree is planted within the radius of the root system of a catalpa. The latter very definitely influences the chestnut tree to grow more vigorously than it otherwise would.
I have recorded my observations of these antagonisms and friendships between trees and plants to show that they are a reality which should be taken into consideration in grouping and transplanting. Such warnings are infrequent because some people may mistake them as condemnations of certain favorite trees. I do not intend them as such, for these plants are often valuable and worthwhile. This ability which they have developed through the many years of their existence is a guarantee of the sturdiness and strength of their family and species, not at all a quality to be condemned.
CONCLUSION
If I had written this book twenty years ago, I would have prophesied a future for nut culture in the north, full of wonder, hope and profit. If I had written it ten years ago, I should have filled it with discouragement and disillusion. Now, after growing such trees for more than 30 years, I realize that the truth lies somewhere between these extremes, but nearer the first.
It is seldom practical to move native trees very far from their natural range, nor is it necessary to do so in this part of the north: We have four fine, native nut trees: the hazel, the butternut, the black walnut and the hickory. In my experience, these four have completely demonstrated their practical worth.
If commercialization is the primary hope of the nut tree planter, he should first consider the large, hardy hybrids, known as hazilberts, which I have produced between a large Wisconsin wild hazel and European filberts. Hazilberts equal the best European filberts in every way, without the latter's disadvantage of susceptibility to hazel blight and its lack of hardiness. They are as hardy as the common wild hazel and are more adaptable to environment and soil conditions than any other native nut tree. They may be trained into trees or allowed to grow as large bushes. Like all other filberts and hazels, they, too, need companion plants for cross pollinization to obtain full crops of nuts.
The butternut is also a very adaptable tree. No one who is acquainted with it, questions the quality of the butternut kernel. In a good variety, the nuts should crack out in halves and the kernels drop out readily.
So many good varieties of black walnuts are being propagated, I need not say much about them, except that many of the best ones are not practical for this climate. Nurserymen who grow them can give the best advice about varieties to anyone selecting black walnuts for orchard planting.
Hickories are the last of these native trees to be recommended from a commercial standpoint, as they are the most particular about soil and climate. However, with improved propagation methods and planting technique they should become some day as valuable as pecan plantations have become valuable to the south.
Considering the nut tree as a dooryard tree, an ornament rather than a business, makes it possible to include many more species as suitable for growing in the north. For this purpose, I suggest heartnuts, chestnuts, pecans and hiccans. The heartnut tree is always one to draw attention and interest, picturesque in its leaves, blossoms and clusters of nuts.
Last, but certainly not least in it potentialities, is the English walnut. I am certain that we shall have some varieties of these which will be hardy enough to plant in the north. When these have been completely proven, they will be a delightful addition to the number of trees flourishing here. What family would not receive enjoyment and satisfaction from having, in its dooryard, a gracious English walnut tree, its spreading branches laden with nuts?
Although the commercial aspect of producing hazilberts is engrossing me at the present time, my greatest pleasure in nut culture still comes, as it always shall come, from actual work with these trees. It is both a physical and mental tonic. I recommend nut tree culture to everyone who enjoys spending his time out-of-doors, who is inspired by work of a creative nature, and who appreciates having trees, or even one tree, of his own. Suggested reading on Nut Tree Culture:
Nut Growing by Morris Nut Growers' Handbook by Bush Tree Crops by J. Russell Smith The Nut Culturist by Fuller Improved Nut Tree of North America by Clarence Reed Annual Reports of N.N.G.A.
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