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.
Building a finely fitted stone wall is a craft that takes time and persistence to develop. In fact, many people choose not to tackle a stone wall as a garden project because it seems too daunting a task to lift the rocks, let alone to fit the rocks so tightly together. There are no shortcuts to this craft, but there are ways to get around the obstacles.
First, select stones that suit your lifting ability. If you scale the size of the rocks down, building a wall is more like fitting together a jigsaw puzzle. And second, instead of fitting the stones together so tightly, adopt a method practiced in England at the turn of the century: fill gaps with small, crevice-loving plants. For detailed instructions, read Build a Dry-Stacked Stone Retaining Wall.
Rock crevices create a favorable environment for growing plants that would not normally survive in your zone. The plants in these pockets are kept warmer and less waterlogged in the winter, and cooler and moister in the summer. The wall has an overall moderating effect on the climate, providing a perfect place for alpine plants, succulents, and herbs.
Although it’s possible to grow plants in a freestanding wall, retaining walls are better suited for plantings because the earth behind a retaining wall supplies moisture to the planting pockets. They are also easier to build because the soil behind them provides good backing for the wall.