Growing ferns on walls is a step more specialized and challenging than rock gardening but may include a number of species suited for both habitats. It appears to be the only situation that will support the lifestyle of that wretchedly difficult (but beautifully photogenic) Ceterachofficinarum.

Wall dwellers tend to prefer grit rather than soil and are frequently seen peering from crevices in venerable old buildings in Britain and Europe. And what a wondrous sight they are. It is possible, however, to build a habitat for these muralists. I find it best to start with very small plants and insert them, along with some moss for temporary support, into crannies, or better yet add them as the wall is constructed.

Brick complements the fern foliage admirably, but stones are more easily managed and offer a handsome foil.The mortared joints (now crumbling) where the European sporelings settled is of an ancient type and neither available nor practical now. Instead, use a lean organic mix incorporating pumice or granite grit (tempered for lime lovers with granules of broken concrete).Until established the ferns must not be allowed to dry out, but once
thriving (says she optimistically) they need only a minimum of attention. Again, the aspleniums are adaptable candidates. Ceterach, if you can find a living plant, is outstanding when established in a sunny site, while Phyllitis and numerous polypodiums
are eminently suitable and attractive additions to shady walls. Good luck!