For years I'd read about "planting a wall", but I'd never done it. So, when I built the drystone wall that retains the grade around part of this circle, I determined to try it. Since this is a north facing wall, I though ferns would be just the thing - and so they have proved.
Polystichum in the Wall
The wall isn't very tall, so the ferns were planted near the top so that they wouldn't get trodden on. Also, since I was new at this, I didn't want to put them lower and risk mashing them as I dropped rocks building the wall. I planted them as I built, not afterward, since this provides the best opportunity for placing and covering the rootball. You want the roots to slope down (as the wall should slope back into the grade) so they can benefit from rain, and you want to plant them firmly so there aren't any air pockets.
It is possible to tuck very tiny plants in a wall, once it is built, but you do run the risk of them being washed out in a heavy rain. Moreover, you have to get pretty brutal with the roots; poking them back into the crevice with a stick or a stake. It's also difficult to be certain you've gotten sufficient soil in around the roots with this method.
You can see the fronds of a Christmas Fern (Polystichum acrostichoides)in the lower right of the photo - it put itself into a crack in the paving and I've left it.
Although they don't resemble each other in the least, both of these ferns are Polystichum setiferum (Soft Shield Fern) cultivars. Just shows you the amazing diversity possible within the same species! On the left is:
Polystichum setiferum 'Plumoso-divisilobum'
I wish this were a better photograph! But, you can get some ideal of the extremely cut and frilled frond. It's a froth of mossy lettuce-leaf green all season, dying back to the crown in winter.
