Green Shoot Grafting of Trees

By Robert T. Morris, M. D. New York

In the course of experimental work with trees I grafted scions of several species and varieties into stocks of their respective genera at times of the year when grafting is not commonly done.

Scions were taken directly from one tree and placed at once in another tree. To this method I gave the name of "immediate grafting" in order to distinguish it from grafting with stored scions which might be called "mediate grafting" indicating the intermediate step of storage. Immediate grafting was successful in mid-winter in Connecticut but I had no thought of making it a practical feature of our work beyond the recording of a research fact.

Immediate grafting was successful in mid-summer in Connecticut. The procedure was very different from that of winter grafting. In summer the new green growth of the year was cut away completely from a scion and the remaining wood of one or more previous year's growth was depended upon for sending out shoots from latent buds. That is what happens after accidents to limbs or to trunks of trees and it occurred in the same way with my scions. Furthermore, it seemed to offer new hope for the propagation of walnuts, maples, and grapes, for example, because the free flowing sap of such species in the spring and early summer has led to attacks upon the sap by bacteria and fungi which ruin repair cells.

I have already published elsewhere the statement that immediate grafting may be done in the way described in any month of the year with many kinds of plants. Exceptions to this rule will doubtless appear here and there. For example, the grafting of trees in August would not be safe in Connecticut because the new young shoots would be killed by September frosts. That is the reason for August cutting of brush by farmers. The tender new shoots that are sent out from latent stump buds become frosted and the entire plant may die.

On account of an illness that had kept me confined to the house most of the time for some months, I had allowed the spring grafting season to pass this year. Stored scions of many kinds lay under a heap of leaves at the rear of my garage. The drying-out process had been intensified by an employee who made a spring clean-up of the yard and who looked upon this heap of leaves as something upon which creditable showing for his work might be made. A month or so later I kicked over the few remaining broken remnants of scions for no reason in particular. Down near the ground I observed that two hybrid chestnut scions which had been trampled into the ground had retained some moisture. Each one had sent out a pale canary-colored shoot of the sort with which we are painfully familiar. The shoot on one scion was about an inch and a third in length with well-formed unfolding sickly yellow leaves. The other scion had a shoot of the same kind but only about one-third of an inch in length and with yellow leaves barely out of bud-bursting form. It occurred to me that my old method of waxing the entire scion, leaves and all in this case, might be done as an experiment in order to see how long these greatly started shoots would hold up if desiccation was prevented and always with the possibility of a surprise.

Some years ago I had waxed some hazel scions from the West that had burst their buds and they all grew but the test was by no means so severe as it was with these yellow chestnut upstarts. The rule of discarding scions that are not wholly dormant was about to be rudely broken; waxing changed the whole situation. A miser does not scrutinize his treasure more acutely than we horticulturists do when getting out scions that have been stored during the winter and the voice of Demeter is calling us to the side of our own wards. How sadly a million nurserymen have thrown away a billion started scions of valuable kinds. My two chestnut scions had gone far beyond the hopeless stage but now perhaps I could be a doctor to them. If my two canary birds could be made to sing then would I also sing.

They were dipped in a dish of melted parafin wax for an instant and then quickly shaken in the air before scorching could occur. The scions were then grafted into a small chinquapin stock. A few days later one of the larger leaves of the larger shoot had cleared itself from the wax coating and had begun to expand widely, turning to a natural green color. The stem of the shoot turned to a normal brownish red. Two tiny shoots then broke through the wax of the larger shoot, looking like axillary bud shoots until closer examination showed them to be scale bud shoots. That should interest plant physiologists. Eventually the cramped leaves remaining under wax coating that was unnecessarily dense finally dropped away useless. The single green leaf and the two scale bud shoots went on to natural development. The smaller shoot of the other scion managed to burst through the wax completely and made normal growth.

After these scions were well under way I went out and searched in the loose dirt and leaves of the old heap and found another hybrid chestnut scion that presented the allusive emblem of a canary bird. This one had a shoot of about half of one inch in length and it burst completely through the wax, to make a fine little twig.

So much for an experiment that led immediately to one of far greater importance. If canary bird shoots could be made to break rules of horticultural theory and of recorded fact perhaps we might note the principle and apply it to the experimental grafting of green shoots of the year in tree propagation. This is what lawyers might call a non sequitur. Such grafting had always been a failure so far as I knew, and certainly my own attempts had failed in former years. Grafting of new growth of the year upon new growth of the year in the growing season is an established feature of horticultural experiment with certain annual plants. Why had it so signally failed with perennial plants and most impressively with trees? Doubtless plants produce in their leaves a hormone which directs certain enzymes that conduct wound repair by cell division. If plants which do not lignify for winter manage to direct successful wound repair after grafting and if plants which do lignify for winter do not conduct successful repair of grafted new growth it occurred to me in a speculative way that the reason might perhaps be sought in the nature of the two different kinds of hormones or of enzymes belonging to annuals and to perennials respectively. The difference might possibly depend upon the arrangement of ions, anions and cations upon two sides of the permeable membrane of a repair cell. The cell is an electrolyte and therefore division of the cell in course of preparation for multiplication might perhaps depend upon an electric impulse so delicately in balance that Nature for some cryptic reason might prefer not to allow the necessary balance to go toward cell division in grafts consisting of green growth of the year in perennials. Perhaps I might defeat natural processes by leaving a leaf or part of one at the distal part of a green graft shoot. This leaf might perhaps elaborate the necessary hormones or enzymes for wound repair purposes—and also for conducting polarity of sap movement toward maintenance of that scion and leaf.

We need not speculate further upon the philosophy of the subject because I took it up at this point for pragmatic tests experimentally. The horticulturist does not have to go to the theatre for thrills. My advance report at this moment comes at a time when a scientist would demand more works along with faith and my only reason for presenting incomplete notes at this time is that they seem to be fascinating in their outlook and no one knows how much experiment may be permitted me for next year at Merribrooke.

The summer was well along when my canary bird shoots opened a vista. The vista appeared at a time of drought when plant propagators wait for better days. It seemed to be necessary to get in a part of the work at least on July 28th and we then had the drought intensified by five more days of great heat, temperatures ranged above 90 degrees F. in the shade and above 140 degrees F. in the sun. After this period of heat and drought we had abundant rains. All grafts were wax treated in these experiments. In no case was an entire leaf left at the distal end of a graft because it was felt that even one-fourth of one leaf would attend to the required functions.

Exp. No. 1. A growing persimmon shoot about two feet long was cut up into scions with a few buds each, and about one-fourth of a leaf allowed to remain at the distal end of each scion, other leaves on each scion being snipped off. Each scion including its remnant of leaf was dipped in melted parapin wax. Two of these were grafted upon green shoots of another persimmon, the latter cut back to make stubs for reception of cleft grafts. Three of the scions were inserted in bark slots in older wood. Note, Sept. 9th, Green leaf part including its petiole had dropped off from all five scions. A small slit in the bark of each graft for investigation showed that the cambium was green in four grafts, the fifth graft was completely dead.

Exp. No. 2. On July 28th three persimmon scions consisting of last year's wood and each one carrying a couple of inches of new growth with a terminal trimmed leaf were grafted into last year's wood on another persimmon tree. Note. Sept. 9th. All three grafts dead including both old and new wood.

Exp. No. 3. July 28th. One green persimmon scion with terminal leaf inserted in bark slot of branch one inch in diameter cut back for purpose. Note Sept. 9th. Dead.

On August 2nd the drought had been broken. All trees seemed to have put up top buds on account of drought and heat. The following experiments were made with green growth of the year but with new top buds much to my regret at having no actively unfolding shoots for furnishing scions.

Exp. No. 4. Aug 2nd. Persimmon tree (a) One graft, green on green; one green graft on old wood. Note. Sept. 9th. Terminal leaves remained green several days after grafting but by Sept. 9th all had fallen off. Small slit in bark showed cambium of grafts still green.

Persimmon tree (b) Two green grafts on green. One green graft in bark slot of older wood. Note Sept. 9th. Terminal leaves had finally died but two of the buds of green graft on green have burst forth into leaf. These will probably winterkill. Green in old wood has green cambium but no swelling bud.

Exp. No. 5 Aug 2nd. Persimmon tree (c) One green on old wood. Sept. 9th. Leaf dead, cambium of stem green.

Exp. No. 6. Aug 2nd. Persimmon tree (d) One green on old wood. Sept. 9th. Leaf dead, cambium of stem green.

Exp. No. 7. Aug. 2nd. Persimmon tree (e) Three greens on old wood. Sept. 9th. Leaves dead, one stem dead, cambium of two stems green.

Exp. No. 8. Aug. 2nd. Papaw tree. Two greens on green, two greens on old wood. Sept. 9th. Two greens on green have buds enlarged and ready to burst. One green on old wood is not enlarging its buds. One green on old wood is dead.

Exp. No. 9. Aug. 2nd. English walnut. Four greens on green. Sept. 9th. Leaflets dead on all. Petiole dead on one, stem cambium green. Petioles bright green on three and the cambium green on these.

Comment. I could not take daily notes which would have been very important. A general statement will cover the point that the terminal leaf on a scion seldom died until it had functioned for at least a week. Some of them functioned for more than two weeks and one of them for at least four weeks, failing only a day or two ago. This would seem to mean that the terminal leaves in scions conducted or helped to conduct repair in green graft wounds to a point where buds are now bursting on two persimmon scions. Two pawpaw scions have enlarged buds to the point of bursting. The terminal leaves on scions seemed to conduct repair up to a point where lignifying for the winter is now going on. This cannot be determined until winter passes but I have never obtained anything like this effect until experimenting with the terminal leaf theory for the first time this year. The most striking effect so far as appearance goes is with the English walnut grafts with their bright green stems.

If I may have opportunity for conducting experiments next summer I shall begin earlier by pinching off the buds of growing shoots, giving them a week of rest and then cutting these shoots up into scions. If buds then start off like those of two persimmons and two papaws they will have time for lignifying.

My whole lesson of this season would seem to mean that after properly checked experiments we may perhaps add what I call "green grafting" to the other form of immediate grafting. The practical feature of this whole new phase in grafting method is an extension of the grafting season to include every month of the year. Scion grafting of perennials in the latitude and longitude of Connecticut had formerly been confined to about two month's in the farmer's rush season, and with general failure in the grafting of some species which may now be grafted successfully.

Letter from Prof. Colby

Agricultural Experiment Station Urbana, Illinois

I regret very much indeed that I cannot attend the meeting of the Nut Growers Association this year. This letter bears my very best wishes and hopes for a successful meeting. We shall miss Mr. Bixby's pleasing and helpful personality. Some time ago I promised to give you a report on some of our activities here and if you think it is worth while, I would appreciate your reading it to the group.

There is an increasing interest in nut culture in Illinois. Wholly aside from the commercial aspects which have been so profitably developed in southern Illinois is a project of recent development, one in Extension work in top working seedling walnuts and pecans with improved varieties. This project is sponsored by the Department of Horticulture, University of Illinois, and the Extension Forester of the State Natural History Survey, with the cooperation of the County Farm Advisers.

Last fall in Gallatin County native pecans of the best grades sold for 18 cents per pound on the market, while the average tree run stock was bringing six cents. With a native pecan crop from one county in Illinois, more or less ungraded, selling for $100,000 in a recent year, thinking horticulturists in the state are beginning to feel that there are potential profits in nut culture where better varieties are planted or top worked. Seedling trees for top working are already growing in abundance in many sections of the state with an ideal climate and soil for northern nut production.

Last year seven counties in Illinois carried on the top working project. This year approximately three times that number have been enrolled. In addition, groups from neighboring counties have been present at the demonstrations. Growers from Iowa and Indiana have also attended. The total attendance has run into the hundreds, both men and women, most of them actual growers.

All the meetings are held out of doors in the orchard or nursery and the group is instructed in the propagation of nut trees through grafting and budding. Nut growers of the immediate locality are glad to assist with the work. After the discussion and demonstration, all present are invited to learn how to do the work by actual participation and many become sufficiently skilled to top work their own trees upon their return home. Possibilities of this type of extension work are almost unlimited.

Letter from J. U. Gellatly

I enclose a short chart or graph of the flowering habits of some of my leading walnut trees. I started in 1930 to keep a record of some of the trees and have added a number since till this year when I kept a record of 17 different trees. The ones shown cover the full time from May 12th to June 25th.

Some new ideas in budding procedure that may be of value and interest I also include herein that others may test them out as I am doing. But even if they fail with me it will not prove that they have no value, for the generally approved methods have failed to give commercial results here.

My main idea was to try to find a new system of handling the budding operations that would give more definite results and if possible to eliminate the use of a wax melter and the waxing of buds. My first trial consisted in the use of florist's tin foil. Cutting bud from bud stick with my new style bud cutter, I cut out the patch from stalk and placed bud in place and with two or three turns of raffia, or rubber bands, secured bud in place, then put 2 wraps of tinfoil around the bud and stalk extending from one inch below to one inch above bud, then with hand pressed tinfoil tightly to shape of bud and stalk, then completely wrapped with raffia and tied securely. This makes a neat job and is pleasant and convenient to work with.

I have today examined some buds so treated and put on the 13th of August and they appear to be in prime shape, no apparent flooding or souring of the bud patch. As this tin foil cost me 25c per pound, I had a happy thought of using cellophane which is much cheaper and is equally easy to use, on the whole, as the tinfoil as, while it is in the first operation of actually applying to stalk not just as easily put on, it has an important advantage that offsets this, which is the ease with which one can see that the bud is in the exact place, while the tying is taking place.

My present method of using the cellophane is to apply a double wrapping of cellophane directly over the bud then to securely wrap from one-half inch below bud to one-half inch above bud. This makes a good air and moisture proof job. Experience may modify or eliminate some parts of this procedure, and it is with this in view that I pass this on that others may take it up and work out the best procedure from a wider experience than one can give.

From my experience I would suggest that if one is marking or cutting the patch on the stalk 8 or 10 days ahead of placing the bud thereon, that one be very careful not to cut too deeply as a large percentage of those I so cut were so badly discolored that I had to cut a new place when placing the bud, as those done 10 days previous showed a one-eighth inch dead and discolored portion around the cut that extend one-sixteenth inch into the trunk of the tree, and no union could possibly take place on such a spoiled cambium surface.