Embellish existing walls with hens and chicks. Just stick a cutting in a crack and watch it take root. Plants with small root systems can also be used.
You have to approach building stone walls a lot like you do life. When you hit stumbling blocks, look for creative opportunities. In wall building, those opportunities come when a rock fits well on all sides except one. Instead of launching a futile search for the perfect stone, just leave it alone. After all, the small gaps left from the not-quite-the-right-size rocks create perfect niches for rock-garden plants.
I learned to build walls from David Erdmann, a landscape contractor in Marin and Sonoma counties, California. He had, in turn, learned the craft as a teenager from an old stonemason working near Lake Tahoe. When David told me that I could put plants in the walls, I queried, “Really? Are you sure they will live?” Well, they did, and this has become my favorite form of wall building. I especially like the way plants settle the walls into the garden, giving them that characteristic, been-there-forever look.