OK, here's what I did to anchor my seeds/plants.
I mixed up a batch of gelatin and kneaded in peat/soil until it was the consistency of bread dough and stuffed it into the cracks on the wall. The consistency was perfect and it seemed to hold the soil and water better because of the gelatin. I smeared a few thyme seeds , violas, and some others. I'm going to insert a few other starts into the mortar...and wait and see.
The recipe for do it yourself peat pots uses gelatin ... it's a great culture medium for seeds because it holds on to water. What the heck-I guess I will see what happens.
In addition to using it to start the seeds-I've spread the geletain/dirt dough in cracks adjacent to the other starts -so that they have something to hold on to when they spread. I'll attach a picture-it's not very exciting-but if the seeds bloom I'll post a few other pictures in a month or so. If it works, I'm going to plant flowers in all of the cracks. Should be fun.
I should have put a few llama pellets in the mix . Maybe in the next batch.