Soft Wood Grafting
Carl H. Phetteplace, M.D., Leaburg, OR
Many years ago Hafdan Lem wrote of a method of soft wood grafting of rhododendrons with which he had had good success. He pointed out some uses and advantages of the method. Nothing further has appeared in the Bulletin about the subject; although, such propagation has undoubtedly been carried on to some extent by many growers. It occurs to me that many, especially among our younger members, are not familiar with the procedure. Since this has been so successful and easily done in my garden for many years, it might be worthwhile to again describe the technique for best success and offer some comments on the subject.
Soft wood grafting can be started in the spring as soon as the new growth is stiff enough to handle, usually in late May or early June. Both the understock and scion should best be in a lush state of growth. From this point on throughout the summer some suitable wood can be found for success; although, the wood may be much harder. Often there is a second flush of new growth in late July or August which is excellent also. Success after September 1st is very poor; though, the plant tissues are soft and would be suitable earlier. Usually there is some cool weather or even rain in the late spring which gives an excellent opportunity for this grafting. This is done out in the open field or lath house wherever suitable root stock happens to be growing and no cover or protection of any kind is used. If the weather should unexpectedly become sunny or warm, sprinkling the plant two or three times a day is advisable. Often in cool weather there will be no evidence of shock or wilt and the scion after a few days will look as fresh as the parent plant even later in warm summer weather. Circulation of plant fluids though the graft site becomes established remarkably soon. The scion will never grow in the year of the graft but when the root plant is cut off above the graft next spring it grows rapidly and will often bud up.
The technique is very simple. The only equipment needed is a sharp, single edged safety razor blade and some rubber tape grafting bands. A small sheet of polyethylene to kneel on is nice. Plastic bags are never used.
A side graft is used so that sap from the root plant will continue to flow past the graft wound to the growing stem above. Ideally the scion should be a little larger than the plant stem making it possible to slice down near the center of the stem for two inches as seems needed. Then fit the wedge shaped scion into place so that all four cambium tissue layers will meet if possible. Practically, this may be difficult as the scion is usually smaller. In this case slice off only a thin layer from the root stem where the diameter is smaller and there is a better chance of matching cambium to cambium on both sides. Sometimes 1 have cut the slice so near the edge of the stem as to have only a thin strip of wood below the bark. It generally works well as it would appear that this offers a larger amount of cambium tissue on the plant to come in contact with the scion. Even though one may be able to get a good cambium match only on one side, the graft will usually take satisfactorily. After the wedge shaped scion is fitted into this side slice, the full length of the graft site is then wrapped with thin rubber tape bands and that is all. It has seemed that the greatest chance of failure is due to giving away of the rubber band near the top so special care is given to security there.
It seems that most anything will do as root stock. Many of the "dogs" that have appeared among my efforts in hybridizing serve well. Sometimes these are cut back severely so they will send out some new growth from near the ground. It is a pity to burn a good root system because the flower proves to be a disappointment. I am never at a loss for good root systems from this source.
This method of propagation would be of little interest to the commercial grower if for no other reason than that the graft may often be a foot or so above ground, which somewhat mars the appearance of the plant for commercial purposes. It was used by both Lem and H. L. Larson, however, for a purpose worth mentioning. Scions from young new hybrid seedlings were taken and grafted in large numbers onto some older mediocre plant which would result in their flowering perhaps years before the little seedling itself flowered, thus getting a preview of what might be expected. But for the backyard gardener it has much to offer. No greenhouse, sweatbox or equipment of any kind is needed. It is an open field procedure. It gives one an opportunity to get a "start" of some rare or very beautiful thing you have seen in a friend's or neighbor's garden. Due to the good root system it grows and may branch readily making it possible to acquire a little stock of something of which you were able to get only one small scion.
Another observation has been that material almost impossible to root can be readily propagated in this way. For instance
R. souliei
has such a reputation that it has been said if you have what may be
R. souliei
try to propagate it. If successful it is not
R. souliei
. However, in early June it grafts as easily as anything else. It has almost seemed to me the harder a variety is to root the more happily it grafts when in soft wood.
Of course, with such soft wood there should not be much delay from the time the scion is cut until grafted thus prohibiting shipping.
All this is just a little inexpensive fun thing that, for me anyway, increases my enjoyment and interest in the garden and may help others who may not yet have become familiar with it. Moreover, it costs nothing.