So after looking around a lot, I finally found those Japanese steel colanders, in 3 sizes, perfect for my Spring repotting and hopefully a root airpruning machine.
Let's see, I'll keep you updated.
Purchased them at DAISO, the Japanese bric-a-brac store chain, easily found all over the world.

Ah...
2 EUROS a piece.

All over the world? Not really I think. Europe has 0 daiso stores..

leatherback wrote: All over the world? Not really I think. Europe has 0 daiso stores..

Oh, no!
Bad news, I buy a lot of gardening tools and accessories at Daiso, very cheap.

I don't get it, why Europe is out?

I just wandering.. It has no side effects for the plants, when those yummy things releasing during the corrosion of the inox (if is in humid conditions constant)?
If no, I have some kitchen tools to transform for the spring..

Felidae wrote: I just wandering.. It has no side effects for the plants, when those yummy things releasing during the corrosion ...

Well, the whole point of using a stainless steel mesh is to avoid corrosion in the short term.
My plan is to keep the trees (including the contest elm) in the colander for one or two seasons, and plastic colanders collapse after a year under UV lights.

Clicio wrote: Well, the whole point of using a stainless steel mesh is to avoid corrosion in the short term.
My plan is to keep the trees (including the contest elm) in the colander for one or two seasons...

If you say it is safe, I’ll give a shot next spring. I didn’t remember if I saw a plant in metal container before, so my curious self unleashed.
Haha, yep! Inox is inox, cause it resists pretty good against corrosion (will rust anyway with time and elements). It is more the oxidation with stainless things, just I typed in hurry yesterday.
Correct me if I’m wrong, but what I remember, the material is stainless, cause of an oxid layer (high chromium) on the surface. We eat with stainless cutlery, so I think it could be fine, just I feel better to speak about if I’m not sure on, before I jump..

Well, the little Elm is repotted in the steel colander. Very draining substrate, the idea is to develop fine roots all over, naturally air pruning the longest ones.
As an additional benefit, even if some soil component breaks down into fines, the colander acts as a sieve and they will be washed away.

Substrate:

I think I will have someone make these for me as I can not get anything like these colanders

I would be concerned about drying out too fast. Now instead of the top being exposed the entire root ball dries out. How often do you water it?