When i was setting up my foam backgrand, i just found it maybe a critical issue that the foam backgrand did not contain any water.
Even in a terrarium, the humidity can rise to about 90% sometime and keep above 70% the most of time, but the backgrand is still too dry for plants to root into.
After some not that successful try, now i think i have get a step on making my foam backgrand "living".
The lines you see is normal cottom lampwick which is always used in an alcohol burner. I cutted these lampwicks and attached them following the undulation of the backgrand from bottom to top.
These lines will work as capillary to transport water from earth to top day and night, the plants beside the lines can suck the water by their roots.
It is safe, cheap and no extra power needed. The only thing i'm not sure is how long the cottom lampwick can keep.
After finishing the construction, i planted some moss and ferns on it. Serveral months later, they are just fine.
A special Onc. also live for these lines