Vertrees devotes several pages in the beginning of his book Japanese Maples to cutting propagation. Apparently he was fascinated by it and spent a good portion of his time trying to work it out. It sounds like he didn't have a great deal of success, but he led the way. He even developed a system of giving the cuttings a short night photoperiod by turning on lights in the middle of the night. I tried that too, but keeping lights working in a mist atmosphere was rather scary, and after awhile it became obvious that that wasn't the answer.
Acer palmatum cultivars, broadleaf at least, are not that difficult to root. You need only adhere to good cutting propagation procedures and be aware that they will not tolerate any mistakes. Any stress will doom your cuttings. No, the problem, at least for me, was getting them through the first winter. I have written a lot about this, they (and tridents as well) form very fleshy first roots that are inordinately susceptible to freezing, yet they need to have a dormant period. This is complicated by the fact that their genetically determined growth cycle is interrupted by the cutting propagation procedure, so they don't WANT to go dormant, but rather put out soft shoots and grow. If you have a very clean cold greenhouse, you may be able to overwinter them there, but mine always died from fungal diseases at those temperatures. So now, I keep them outside but control the minimum temperatures with my freeze control system that I described here or elsewhere recently, I forget where. Anyhow, this system keeps the winter temperature at 26F and above, but the cuttings are out in the open air, getting winter rains, etc, and allowed to go dormant whenever they want.
There are a number of other tricks, but most of them still fall into conventional cutting propagation practices. The condition of the wood is extremely important. You want very vigorous shoots, semi-hard, from young trees, even juvenile wood works well. You have to catch it at just the right stage for really good rooting ability. Bottom heat speeds the rooting but doesn't seem to give you more rooted cuttings. I once hit it right with 'Bloodgood' and got almost 100% rooting initiated in ten days. I have never done it again, but I still do get good results when I pay attention.
I am just getting started on A. palmatum cuttings again after an eight year hiatus from moving the nursery. Last year was a good test batch. The results weren't spectacular but I did get some rooted cuttings of 'Seiryu', 'Bloodgood', 'Yuri Hime', 'Kiyohime', 'Shir Autumn Moom' (A. palmatum X A. japonicum cross I believe without checking), 'Ibo Nishiki'. My big problem now is to get my stock plants pumped up for better wood.
Years ago, there was an excellent Oregon nursery called Wright's whose specialty was cutting grown Japanese maples. It was like heaven. They had a list of about 30 cvs including some dissectums, including 'Inaba Shidare' as Nigel mentions, and also 'Viridis' (a really crappy cv). They even had 'Shishigashira', although they never grew strongly on their own roots. They were about $2.50 each in liner pots, a steal. But then the old guy who owned the place died and the kids didn't want to take it over, so it folded. I could have cried, but it did get me doing it myself again.
Nigel mentions wounding the cuttings. Most sources recommend this, but what I have found is that wounding created rooting mostly along the two sides of the exposed cambium, making pretty lousy rootage for bonsai. I have found that it really isn't necessary; the strike percentage is about the same without rooting (but slower), and the rootage is better. I don't bother doing it anymore. Hormone strength is crucial and related to the condition of the wood and the particular cultivar. I use either Hormex 16 or 30 most of the time (1.6% and 3.0% IBA). Liquid concoctions were useless for me since to get the IBA strength necessary I also got necrosis from the solvents.
It's fun and exciting work, and I hope to have a few of these cutting grown plants in the catalog in the future, although I won't sell them until they reach one gallon size, I learned that lesson over the years: when dealing with rare difficult material always grow it out to a size to achieve the maximum return or you are just giving it away. Right now I have some pretty handsome 'Ao Kanzashi' in one gallon from cuttings. Two years ago I had one gallon 'Yuri Hime' and 'Kiyohime' and they just flew out the door. I thought the price was somewhat exorbitant, but apparently everyone else thought they were cheap.
Brent
EvergreenGardenworks.com
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