Ok touching upon kanuma vs peat once more...
No professional satsuki importer or grower that I know of uses peat most, moss peat, or sphagnum moss in their soil mixes.
Almost 100% of all plants in the rhododendron genus here in Europe are grown in peat moss. The only exceptions are bonsai people with their satsuki, who use kanuma.
I think the same is true for the US.
Doesn't do much for the roots, can become hydrophobic and/or mush that prematurely clogs drainage.
There is a big difference between freshly dried sphagnum and actual peat moss. I agree that I do not see the benefit of adding sphagnum moss to kanuma. The strings of sphagnum will become hydrophobic when they dry.
I think adding actual peat or coco coir or pine back to kanuma will work better. But I have never tried. But you need the stringly peat, not the milled form. If you add milled peat and kanuma, you need to use mostly peat and a little bit of kanuma. Otherwise, you will wash the peat out of the kanuma towards the bottom. And it will act like peat clogging up the kanuma rather than kanuma making the pear more airy.
I've bought satsuki from
Rick Garcia and
Dave Kreutz and also know of a grower who travels to Japan to work with satsuki masters there. I've seen their trees, none have anything but kanuma.
While sphagnum moss is locally available and mostly cheap, it's not really optimal for satsukis.
Satsuki are just like any other rhododendron species. They do well in peat. It is just the bonsai angle, with shallower pots, and with a substrate over soil mindset (rightly or wrongly), and the availablity of kanuma as being literal dirt and a literal waste product, that made it an ideal substrate for satsuki bonsai trees. For satsuki plants, peat works perfectly. I grow almost all my plants with either pure peat, a potting soil based on peat, eriocacious compost based on peat, and perlite. Recently, I added a small amount of pine bark chunks. Note, these are not bonsai. From my experience, plants in kanuma need more care, more fertilizer, more water, and are more prone to chlorosis. But this can be managed perfectly well with a more intense bonsai care regime, with more watering and a steady (dilute) fertilizer regime
I was a skeptic at first too about kanuma, but saw immediate improvement in my satsukis when I put them in it. I use it in a climate that is colder and hotter than yours. You would have no issues with it.
It also might be worth getting Rick's
book. It is the most comprehensive English-language satsuki bonsai book published, from what I've seen. I have most of the others, none are nearly as good at explaining WHY some stuff works with satsukis and how to grow them.
There is no reason to be skeptical about kanuma soil for azalea bonsai. It is a tried and tested method which should work for most climates, as long as you combine it with a watering and fertilizer regime suitable for a substrate based approach.
But agreed that the most common Japanese use of moss is to surface pad the kanuma soil after a repot. And not so much as something you mix in. There are 50+ videos on Youtube of Japanese repotting satuski bonsai in kanuma. Some of them add moss on top. None mix moss through the kanuma. Doesn't mean it can't work. I think Callaham's book also suggests mixing in sphagnum moss with kanuma. But once you sphagnum dried up, you'd be better off without it. Though if you can keep the sphaghum moist all the time, it should be an improvement for dry climates.
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