Its a technique I saw Matthew Ouwinga doing. Basically the idea is to layer over the top of the washer once it starts to constrict the trunk.
As the tree bulges over, it produces roots over them. You can then cut the roots off below the washer leaving you with a big base and nice nebari from it instead of the crappy roots form being grown as a seedling without root work.
I buried it about 2-3 inches this spring so it can root.
I've seen others try just wrapping wire around trunk, CDs, etc to constrict the trunk.
I got couple hundred Japanese maple rootstock for grafting a few years ago. Since I didn't have a lot of time to graft and wasn't great at it because of travel they were just getting overgrown and growing into the ground. So I thought I would try this technique on them.
I wanted something that I didn't need to worry about once I buried since I tend to leave things for awhile so I went with washers.
@NOLAnovice Sure will.
I planted all of them in a grow bed this spring. Totally grown into a monster of green now that I got them out of 4in pots. Also daily irrigation is helping quite a bit also.
Once the leaves fall ill post some pictures so we can see if they trunks are starting to dig in at the washers. The washers are still mostly above soil. I am going to build up a 3-4 inch wall and fill with good "Bonsai" soil for an inch or two above the washers this fall/winter and then let them grow one more season. Then net fall start checking a few for roots over the washers.
If doing just a few I would use pots but taking care of a lot is a pain so going with the grow bed option.
Key is going to be getting them out once the roots are formed but no to long afterwards so they don't get out of control. I a pot this would be a lot easier.
