I wonder if anyone can offer some advice on how to clean this up. This is a graft of Acer tenellum, the Delicate Leaved Maple, which I purchased in 2011. It is grafted on platanoides. Over the years, the graft has lived but never grown much, and the understock has consistently put out buds -- and sometimes leaves if I don't rub the buds off fast enough -- until it has the growths that you see in the pictures, taken one from each side of the understock. The understock had been pruned in these areas originally, which is not ideal but usually not too much of a problem if the graft grows well. Tenellum is known to be extremely hard to graft, and the other plant I got at the same time languished for a couple of years before really taking. However I was able to plant it during the winter of 13/14, and it is now growing well in the ground although it's still a small shrubby plant. I'd like to try to get the understock to stop putting energy into bud production, though I understand part of the reason it wants to do this is because there is only a small root. So the way I see it, my options are: 1) cut off the "knobs" and seal with some kind of putty, or buddy tape. 2) paint the knobs with sealant 3) bury the whole thing up to above the graft, over about 3 years, to get it to put out it's own roots 4) let it put out a platanoides shoot to help root growth I could try and air layer but the scion is very thin and weak. So, advice would be appreciated! Thanks in advance. -Emery
This is symptomatic of the scion (acer tenellum) not having a strong enough auxin flow from its buds to suppress budding in the root stock (acer platanoides). Weak root growth also results from inadequate auxin flow. Auxin is made by the buds and leaves and travels down the tree as a signal of 'life above' to stimulate root growth. Platanoides apparently requires much more auxin than tenellum produces. Your option #1 and #2 will not be effective as sealant will do nothing to stop budding unless it kills the stock locally (which, in turn likely kills the whole tree). Cutting the knobs off amounts to pollarding; likely it will only get worse over time. Conceivably bud making tissue could be eliminated from the platanoides root stock if you strip the bark off, say, two sides of the platanoides and promptly covering with HDPE film (visqueen) that is kept in place until a new epiderm has formed (10-15 days) and, in the subsequent year (or maybe with another year's delay) strip the remaining original bark. This possibly an interesting idea, but it will do nothing for the vigor of the tree. It would only have aesthetic effects in the end and the new bark on the platanoides very well could be ugly for a long time. Option #4, let the platanoides put out shoots, will certainly make the root stock more vigorous. My suspicion, however, is that the tenellum will continue to decline. But maybe not. Budding is very dependent upon nitrogen nutrition, which is supplied by the roots through the xylem (wood) sap. So, possibly extra letting the 'suckers' grow and a bit of supplemental nitrogen will make the tenellum more vigorous too. Layering, that you allude to in option #3, is the only practical remedy, IMHO. However, you do NOT want to BURY the platanoides as this will suffocate the roots, quite possibly. You want to remove a ring of tenellum bark, above the graft union, leave it stand open to the air for a few days (to kill residual cambium cells that cause the girdle to be bridged), then pack a damp substrate around it. Damp sphagnum moss tightly covered with plastic is the most care-free but a plastic pot split and fitted around the stem and filled with your favorite rooting medium may be preferred. Then, if the tenellum has hardened foliage, you wait at least 6 weeks and maybe as long as a couple of years for new roots. Once enough roots have grown to sustain it, you then sever the tenellum from the platanoides root stock and plant it (with support as you would any new tree). In my experience, most trees' roots only have sufficient starch reserves to survive for about 18 months, not 3 years. So, it is preferred for layering the tenellum that there be some foliage below the girdle (marcot) that sustains the roots = just let those 'suckers' grow! Short verison: Let the platanoides 'suckers' grow. Marcot/air-layer your tenellum off the platanoides root stock. I think you could affect the layer now and the platanoides will sprout, though waiting until next spring to do so would be the more conventional timing.
Thanks for the lengthy and thoughtful reply. I had learned about auxin flow but wasn't thinking about it, always great to get reminders of the processes. Just to clarify, #3 doesn't have anything to do with air layering, and it is a standard method to get rare maples on barely compatible grafts onto their own roots. This method is practiced the world over, and works if the scion has enough strength to keep going. The trick is to bring the soil level up slowly until you can get the graft union on the ground, then the plant basically layers itself. I know it's counter-intuitive given how we warn constantly about planting too deep, but it is a technique that's available. I didn't give air layering a number because I fear the scion is too weak support itself after the cambium is cut. Certainly an option is to try and get the scion a little thicker by letting the base sucker, but as you note the fear is that it will just die off. BTW I have tried some nitrogen jolting (powdered algae) but it has never had an effect on the scion or roots. At least not yet. I gave it some osmocote this spring. I wouldn't try to air layer it before next year at this point, in any case. -E
Thank you, emery. I was completely unaware of it. It is quite interesting to me that it works - sounds similar to the way rice makes new roots in the paddy. Indeed, it is counter-intuitive. Fascinating stuff, trees.
Not experience with either maples, but am good friends with a great grower. When trying to get a tree form maple they use a thick plastic trunk wrap slightly larger than the trunk caliper to shade bark and prevent buds /new growth from forming on the trunk. New buds don't form when shaded. If the scion wood is sparse, the understock is getting lots of sun; that in combination with the liability of each maple is further complicating things, which leads to all the back budding. So maybe cutting sun out of the equation for the rootstock may help eliminate the rootstock budding issue, but with that said I stand by my first sentence.
