Robyn Laing, who lived in Japan for 30 years and who is leading the Cherry Blossom tour again in April (the same tour I went on last year), has been in touch after reading the posting that included kokedama, a Japanese method of putting house plants in balls of earth.
Robyn sent me the Japanese characters for kokedama and I’ve found this good YouTube video (7 minutes 29) on how to make a kokedama. It’s almost a purely visual demonstration with the odd subtitle in English.
The original article I linked to noted that in Japan “the clay-based akadama bonsai soil” is the basis for kokedama. If you’re keen it might be worth getting in touch with the local Bonsai Society to see if they have a supplier.
Here’s a written (with photos) tutorial, although I would suggest watching the video too as they have some cute techniques, such as using newspaper instead of gloves.
The key point seems to be that the moss balls should never dry out and so shade-loving plants are the best option.