Grafting: A Surgical Cure
Part I: Why To Reconsider Grafting
Scotch Plains, New Jersey
Some rhododendron varieties are genetically "bud hardier" than others. Some are genetically "plant hardier" than others. I ask that you also consider that some rhododendron varieties are genetically "root hardier" and/or "soil hardier" than others. Now that we have been testing rhododendrons on their own roots for about 40 years, I think that many of you can recognize that not all varieties are equally equipped in the root zone.
Here in my area, I have noticed that there are some varieties that do extremely well at putting out roots into heavy soils. They have tough, vigorous, healthy, adaptable, disease resistant, easy to please roots. You don't have to go to bizarre artificial extremes when planting them, and you don't have to look forward to years of close vigilance and extra efforts in order to maintain them. Given a reasonable effort at planting time, they get established quickly, and then you can pretty much leave them alone.
I have also noticed that there are quite a few desirable varieties that are bud hardy enough here and plant hardy enough here when their roots are happy and healthy, but in the long run it is difficult or impossible to do well with them because of root hardiness and/or soil hardiness problems. Improved cultural techniques help, but some varieties still won't work out unless you go to great extremes. In going to great extremes to improve culture, you have to deal with certain considerations. How much can you spend on peat moss, pine bark and sand? How much effort can you put into each planting hole, or are you willing to make raised beds? How much effort (and possibly expense) can be put into continuous additional mulching beyond that which is provided by nature? How much can you do to achieve better drainage or improve soil texture or maintain cooler soil temperatures? How much do you have to fight the natural conditions on your property in order to artificially create conditions that are not natural on your property?
Obstacles vary in different climates and with differing soil types. Improved results may only be temporary. For instance, organic material "disappears" through decomposition faster in warmer climates. In some areas that have hot summers with substantial rainfall it disappears much faster than some of you from other climates can even imagine. In the Pacific Northwest, I have seen "heavy soil" rhododendron gardens that convince me that it is much easier to grow rhododendrons elsewhere in heavy soil than it is to do so here in my area. Can plants "elsewhere" cope with heavy soil better because they are in a climate where they are less stressed by winter cold and/or summer heat? Is it because the soil does not get as warm or as cold?
In my high school biology course we were taught that plants have various "organs" just as animals have various organs. Instead of kidneys and hearts, etc., plants have roots, stems, leaves, flowers, etc. as the "organs" which perform the various functions of life.
I don't remember how it started, but at some point in growing rhododendrons it began to amuse me to use medical terms when I was dealing with health problems. Terms like intensive care, therapy, rehabilitation, nursing, surgery, etc. Along these lines I say that many rhododendron varieties seem to be so handicapped here by genetic birth defects of the root organ system that they can never lead normal lives here. Should I continue to attempt to prolong the lives of these patients by putting them on expensive, labor intensive, extraordinary, artificial life support systems? Should I pull the plug and let them die? Is there any hope of a cure? So I began to experiment with organ transplant surgery in 1989.
Organ Transplant Surgery
It's working! Organ transplant surgery can be a cure, but currently operations can only be performed successfully when done early in the life of a patient. Surgery can be performed to give juveniles a hardier, more vigorous, more adaptable, disease resistant, easier to please, healthier root organ system from a good strong organ donor so that they can go on to lead more normal, healthy, productive lives with a longer life expectancy.
This organ transplant surgery is also called grafting. It is different from the rhododendron grafting of the past. It is grafting intended as a cure and not merely as a method of propagation. It is better than in past. In the great majority of cases it is now possible to perform this surgery without developing any of the complications or undesirable side effects reported in the past. It works like bone marrow surgery, where you give the patient a little piece of good material from the donor and then the patient can grow more. The organ donors are not seriously harmed and there is no need for deceased accident victims.
However, here in the Eastern USA we have been taught that: most rhododendron varieties perform better on their own roots, there can be incompatibility problems between scion and understock, graft unions are weak and can break, growth of suckers from the understock can take over and crowd out the desired part of the plant, and grafting is difficult. As a result of this education, grafting rhododendrons has not been practiced much here for over 40 years, and there are probably many members who have never even seen a grafted rhododendron.
Progress Marches On
Shouldn't it be possible to achieve better results from grafting today than 40 years ago? Look at the progress that has been made in human heart transplant surgery. I'm not a doctor, I'm not a scientist, I'm not a nurseryman, I'm just a hobbyist who has been up to some mischief at home. But by doing things differently, I have found that I can make grafted rhododendrons that: perform better when grafted on a strong understock than they ever could on their own roots, don't suffer from incompatibility problems in the overwhelming majority of cases, have graft unions that are stronger than the "normal" stem areas by the end of the second growing season, and never produce growth of suckers. I have also found it is relatively easy for hobbyists to do this in the home (I produce my grafted plants in the basement under fluorescent lights). Furthermore, I think that any compatibility problems that arise can be solved by further experimenting.
In the old days everything was grafted onto 2-year-old seedlings of R. ponticum, whether the scion had "type P blood" or not. In modern transplant surgery you endeavor to use a donor with a blood type that is compatible with the blood type of the patient, and sometimes only close relatives are suitable as donors. Operations where some closely related species are shared in the ancestry of both scion and understock are usually problem free. If there is still a problem in a certain combination, it can be solved by experimenting with different understocks. In my area where almost everything we grow has to have some blood of Ponticum Series or Fortunei Series species in the background, I don't think that we are going to need a lot of different understocks. We just won't put scions of all varieties on the exact same understock in every single case.
Strong Graft Unions
Better compatibility may also be a factor in getting strong graft unions. I am not having a problem with weak graft unions. I have read several accounts of the old practices in use when this complaint originated and I see that the procedures that I have come to favor through my experimentation are different in many ways. Among other things, they grafted low onto seedling understocks, putting current green barked wood on older brown barked wood, much or most of the grafting was done by employees at nurseries who were expected to produce great quantities at great speed, and it was standard practice to remove the bindings from grafts after four weeks. I graft higher onto cutting understocks, putting current green bark wood on same age green bark wood, I work leisurely in endeavoring to make the best cambium matchups that I can, and I leave the bindings on for six to ten weeks. I could go into great detail about the significance of these differences, but I'll keep it shorter. In grafting to cure root problems, I graft higher as I don't want dual root systems. I want the unions high enough to prevent the scion from ever putting out any of its own "poor" roots, as doing so might weaken the relationship with the understock and cause compatibility problems or even "rejection" of the donor organ, and the poor roots may be more susceptible to root diseases and thus be a source of infection that could kill a plant that I wanted to make resistant. In July 1993, some kind of animal chewed practically every leaf and many branches off of about 20 grafted plants that had been started in the fall of 1991; several were completely stripped of all foliage and all green bark. After a month or so, some were breaking out new growth, but 11 of them had died. However, this incident also provided experiments to learn from. First, I was happy that none of them was able to break new growth from below the graft union. This reinforced my confidence in a "sucker proofing" technique which will be discussed shortly, it also gave me 11 main stems to use in a breaking test and I found that none could be broken at the graft union. A "normal" stem section above or below the union would always give in first. It was like the wishbone from the dinner turkey not breaking in the middle. I should point out that after callusing and healing many graft unions will be a bit thicker than the stem sections above and below the union. Also, I suspect that in my climate only grafts that are off to a good start will survive. Those with inadequate callous fusing due to poor cambium matchup, or loose binding, or premature removal of bindings, or fungus infection in the graft union just won't be able to pass enough juice through the graft union to survive the first summer outdoors. With a little practice and experience one can quickly learn to recognize the tolerances for cambium matchups, how tight is right for the binding, good "callous fusing" and to practice sanitation that minimize fungus infection. You can get to the point where most of your graft unions in any given batch will be well healed and sealed and fairly strong and difficult to break right in the early stages, and most of the remaining grafts in the batch will be off to a good enough start to make it, although some additional sealing will have to take place outdoors. By the time that the second summer's growth is out, the strength of the unions is no longer a concern.
Total Prevention of Suckering
There are two methods for preventing later growth of suckers from understocks of elepidote rhododendrons. One method has been known for a long time. However, it has seldom been practiced. It involves digging and taking sections of root stem from the root system of the donor variety that you wish to use as your understock and grafting the scions onto these root sections. Elepidotes do not have the ability to sucker from root sections that never had any foliage or dormant buds on them. I have experimented with this. It does work and I have produced some fine plants this way, but it is not as easy as the other method and the percentage of success is lower, or at least this was the case with the roots of the varieties that I tried. Root sections have very hard wood and I tended to cut my fingers more frequently when working with them, as I had to press harder on the razor knife. Those that I tried did not form callous as well as understocks with green bark and foliage on them do, so it was harder to get good callous fusion. Because they have no foliage, root sections will not stay alive indefinitely as an understock with some foliage will. A root section will die if there is not some fairly quick callous tissue contact with the foliage scion above it.
The other "sucker proofing" method has evolved more recently. Others have written of removing dormant buds from an understock in an attempt to reduce later suckering. I have taken this concept to an extreme which has resulted in actual sucker proofing. It couldn't be done when grafting onto seedlings but works when grafting onto an un-rooted cutting of the understock, which is then rooted after the scion has been attached. The graft union is then in the process of healing together at the same time that the understock is in the process of rooting. It also works with pre-rooted cuttings of the understock if they were intended as understocks and specially prepared right from the start to accommodate this method. They have to be prepared and stuck differently than in the standard practice. The "basic" idea is that by the time you move your newly grafted plant outdoors to grow on, you have cut off the terminal rosette section of the understock cutting and you have surgically removed all of the dormant vegetative buds, all new growth, and all of the leaf bract scars on every remaining part of the understock. Leaf bract scars can conceal dormant buds. These dormant buds, new growths, and leaf bract scars are cut out by making deep notches which remove a wedge of the bark and some cambium from immediately beneath. Some of this must be done before the understock cutting is stuck for rooting, some at the time when the scion is attached, and the remainder at any time you please after removing the bindings, even immediately. You end up with your scion grafted to an understock made of a rooted stem section that has no remaining old rosette areas of its own and not a hint of a vegetative bud. The relatively small notch wounds heal quickly and easily without causing any difficulties. Not a single plant prepared by this methodology has been able to send out a suckerónot for me and not for others who have been shown how this is done.
I have seen that some rhododendrons can put out vegetative growth from crown gall callous tissue, but this is very rare with rooted cuttings and I don't think that this poses any significant threat to the reliability of sucker proofing. This phenomenon is more apt to turn up in seedlings and tissue culture plants.
Disadvantages of grafting.
There do not have to be any disadvantages except that preparing grafts is slower than preparing cuttings, which is not necessarily a disadvantage for hobbyists who may find it more fun and interesting. Also, you may have to set up a better "sweat box", "humidity tent", "propagating enclosure", or whatever you call it and add a couple more frills than are required for only rooting cuttings, and you might cut your fingers more often in the beginning.
You don't need a greenhouse. You don't need bottom heat if you can set up in an area where the temperature rarely goes below 60 °F., which is not too hard to manage in most homes. And you can bypass having a plumber install a water line with automated mist sprinkler heads by other simpler do-it-yourself means. I use fog produced by a small inexpensive home appliance that is readily available in stores for about $50.1 will mention other possibilities in the "how to" article. Some of you out there will undoubtedly figure out other ways around this, once you see the concepts involved.
Advantages of grafting.
You can make plants that are more root-rot resistant. You can make plants that are healthier "better doers" than they are on their own roots, and probably even transform some into outright "good doers." Grafted plants on tough understocks are more resistant to fertilizer burn and mineral salts problems. All of this is evident in a test I have been running with several pairs of plants that are same age, same variety, identically treated, and side by side, but one is grafted and the other is on its own roots.
And have you ever noticed that some varieties are "bud hardier" and/or "plant hardier" once they get out a decent root system? You can stop the extreme struggling required to artificially create "absolutely perfect" soil conditions for many varieties. Why face years of struggle if you can have an easier-to-please plant right in the beginning? A plant that will thrive in a decent location if given a decent planting, without requiring the difficulties of achieving "perfect" cultural conditions.
You can propagate varieties that are difficult or impossible to root. You can be more successful at propagating. Some of my best "root hardy" understocks have also turned out to be very easy to root, and after a little practice, I have found it is easy to have 90 percent of my graft unions take. Success is almost certain when grafting onto an understock cutting which has already started to put out some roots. Then the graft union can heal while the understock goes on to become well rooted.
I am seeing the advantages of grafting here in my "amateur" trials, and in Germany they have been doing fine with grafted plants for a much longer time.1
This has been a basic explanation of why to graft. The details will follow in a "how to" article with illustrations.
1 Encyclopedia of Rhododendron Hybrids by Peter and Kenneth Cox, Timber Press, 1988, p. 83 (taken from comments about R. 'Cunningham's White'): "Used as an understock in Europe for grafting hardy hybrids. The increase in health and vigour imparted by the 'Cunningham's White' is very evident in the Ammerland region of N. Germany, and this suggests advantages of an increase in (the practice of) grafting hardy hybrids for severe climates of E. North America. This method of propagation (when using 'Cunningham's White' as the understock) is said also to have a dwarfing influence on many normally untidy growers, and to impart alkalinity tolerance."
The Germans do a lot of grafting. Do they know something that we don't? They get increased health and vigor as well as a dwarfing effect and alkalinity tolerance by using R. 'Cunningham's White' as an understock. I have not been using 'Cunningham's White' as an understock because I do not consider it to be a good "tough root" type here in a hot summer area with heavy soils that get much warmer in summer than the soils in Germany. With the tough and vigorous root types that I have been using as understocks, no dwarfing effect is evident. But I am getting increased health, vigor, root rot resistance, and heavy soil tolerance. Perhaps other "dwarfing rootstocks" can be discovered that may be suitable in areas where 'Cunningham's White' is not good enough.
Bob Bondira, a member of the Princeton Chapter, has been growing rhododendrons since 1975 and has experimented extensively with "at home" cultural and propagation techniques. He has also spent much time outside his own back yard studying other rhododendron plantings, especially in the area from New York to Philadelphia. He frequently speaks to other chapters.