Plants surviving on expanding foam?

Hi all! I'm looking to try to DIY a decoration for my aquarium for the first time, by creating a cave using expanding foam. The hope is to add plants such as Java moss on the top/side of the cave itself, but after watching a few videos, I'm unsure whether the plants will be able to survive on there. Does anyone have any experience with this?

Another issue is that I learned of the idea of putting sand over a layer of dirt after I had put my fish in the aquarium. If I were to need to add some garden soil onto the cave for plants to grow, is it difficult in a live aquarium?