I bought two bags of Rockwool 10 years ago - one was retains water the other resists water. Personally I didnt have any luck with it but did not have anyone to show me how to use it. The Bags of material are out there taking up space. Keep posting, maybe I will learn how to use it from someone who is successful with it.

Camille, you are the number one :D Thanks!!!

Yeah there are actually quite a few different vertical wall companies in Australia, but all of them use either that foam or a mesh or some other thick inert material that the roots can grow into and be protected. The French guy uses a thin felt that the roots actually grow -on- and stick to.

My brother worked on a landscape design project for a big apartment complex and looked into it, but found that the felt dried out too quickly and used too much water. He submitted a design that used a mesh/inert system for a green wall surrounding the entire entrance to the building that would use less water and work better for our climate. Only problem is that with more surface area to fill, these systems are much heavier and hold more water at any one time, meaning you have to stick them on load bearing walls and you can't just cover entire outside walls with them unless they're designed into the building.

Gardening Australia - Fact Sheet: Vertical Gardens

I see what you mean, it is quite a technical project especially catching the water and then pumping it back up and the weight bearing issue!
I wonder if an indoor green wall will smell damp?
Overall, it is probably better to plant water wise native plants, if one wants to be 'green'... but the vertical green wall is so pretty...:hmm
Let me go away and work on it....:scratchhead:

Maybe someone out there can refresh my memory. I seem to remember several years ago a fiberglass potting medium called "Grodan" which was being sold as a fiberglass and sold in two forms; one was 'water adsorbent' and the other was 'water repellent'. I believe the idea was that be varying the percentage of each in a mix you could control the water retaining ability of your mix. I don't know if this material is still being sold but I purchased some several years ago and gave up on it after trying to repot one plant. I still see something like this in some of the seedling Phrags I receive which I believe Magnus touched upon.

I think you hit the nail on the head, Jerry!