It depends a lot on what trees you're talking about... a few tropical types are happy in moss, but most would prefer something more substantial, with lots of grit, bark bits and perlite, unless you can afford Akadama (which you'd then use 100% for the whole mix in some cases).

I know of two reasons to use it...Moss as a cover topping for above soil... As well as used to help develop air layers...what was this persons reasonings for doing so? Because...I can't see it being quick draining but holding much moisture. (Which I have on one of my pots to keep the pot from drying out in the sun so quickly) But, in all honestly I would be concerned with root rot. With how it stays moist...as well as you would have air pockets...for it doesn't compact well.

Were they attempting to work on the roots of their tree? Develop them more? I just can't see the purpose in wishing to plant a tree in just that. I see more complications from long term use of having such organic matter as that for a soil substrate.

Was he propagating them? I can only see someone doing such a thing...for a desired purpose. Not just planting a tree in it to allow it to be bonsai material...for root rot is a problem with organic soils with some trees.

Putting sphagnum (or any moss, or pebbles) on top of the soil is something you'll find at Wal-Mart, on imports from bonsai 'factories' in China, etc. who export millions of them all over the world without much thought or care to what happens once they go home with newbies. As I said, there is a place in certain plants for sphagnum to be part of the mix, but in general is not noted to be a routine part of the majority of bonsai'd trees. Any time I do buy a plant with moss on top, I generally leave the moss at the store, or remove it immediately.

I had a kojo no mai arrive from Planet City Bonsai. A bonsai enthusiast,an older experienced bonsai man named Steve who owns the place sent it with the moss. To help ensure the roots kept most and not dried out to much in the shipping process...as well as in the sun once in my care. With it having a major root prune prior to shipping.(Before sun was really a concern since I was wintering it inside with it coming from a warmer climate. But...would come in handy once placed outdoors) When I called to let him know that it had indeed arrived well and intact. I asked him about the moss. He explained why he had added it to the pot and to why I should allow it to stay. So no I agree not common place...but, it has it's purposes for specific reasons. As Steve informed me.
I agree...it is known for box stores to have it added...not really the spagnum moss in my general area. But some sort of glued on moss. But...I do know many from bonsainut.com who place it...or even lava rocks on their substrate to help keep the roots from burning out in the sun. Depending on the tree...and their zone or the species of tree it may be. But, not common place to plant it entirely in the substrate of moss.

Hi
have used sphag for many years in fact I wouldn't try to dwarf with any other method lol Have a powder puff and ficus that are 3o years old
My main goal was to dwarf the tree while allowing it to mature
The secret is to wet the sphag then compact around the roots I use drip trays with holes You need a good brand of sphag the cheap ones are mostly sticks
Many many advantages to growing this way particularly outdoors Would think it works best on tropical trees??
gary

I posed this question at another bonsai forum...for I had never heard of such a method. With substrate coming up often and even debated as which mix is the best method...Here was one reply...thought worth sharing.

"Back in the 90's, and perhaps it was shot in the 80's, there used to be a public television show about Bonsai, maybe it was called New Horizons in Bonsai?? The host, Brian Batchelter(?), potted all his trees in SM. He actually had some pretty nice stuff..at least I thought so at the time.

I think he was out of Fla and the vast majority of stuff he worked on was tropical. He died a few years ago from the respiratory disease that can be contracted from breathing dried SM...perhaps that is all we really need to know right there!!

Years ago I tried this with several trees...again mainly tropical and I also tried Bald Cypress and Water Elm. The trees survived but never thrived...like inorganic soil mixes it is up to you to provide all the nutrients for the trees. Of course the SM holds a lot of water but it also dries out quickly so I never had any issues with root rot."

So...it can be done...many stated not common practice. You can see one poster said he had known one who had great results from it. As well...as the issue of his death. May not have been related to bonsai. One can only speculate. That said...if you were to go with SM for substrate in your bonsai. I would wear a protective mask...to just rule out any possibilities of anything.

If you do use SM as a substrate...please journal it and report back to let us know how well you did with it. I am myself curious...not enough to use it as a substrate. But am curious about how it goes for you. Wishing you the best of luck.

Hi
have heard that rumor many times lol. If true there should be thousands of dead people SM is a standard potting for most of the orchid industry and has been for over a hundred years I personally have used it for over 40 years .
both dried an live moss. Whatever lol gary

I don't think it was a rumour (heard it years ago) but a story about someone who possibly was particularly sensitive or even developed an allergy (which can happen to anyone anytime to anything) which affected him. We weren't there and can't say... but you can believe what you want of course.