Crevice Gardens

Crevice gardens are a variant of the rock garden.  I don't know a lot about them but I do know they look beautiful. 

They are literally vertical rock gardens and often mimic the look (and accommodate the flora) of naturally fissured and cracked bedrock outcroppings. Flagstone sandstone and limestone (or split layered granite) is bedded on edge at least two feet deep buried in and back filled with sandy loam or pit run.  The rock edge faces are set flush to the ground and placed in groupings to create narrow crevices and veins of soil. Crevice plants don't thrive in good soil. There are many dwarf cushion plants that prefer this environment, including some of the most beautiful alpines. Sedum is also very fond of this type of dry rocky terrain.

Apparently cracks and crevices in cliffs and mountain peaks give protection to many plant species. Alpine plants grow happily in sun warmed natural crevice gardens in a summer that may last only a few weeks. The solar heat absorbed by the stone adds a few extra days to the growing season as well.

A crevice garden can be a great alternative solution to a typical stone retaining wall for accommodating the change in grades of a hilly garden while also providing an environment for some more unusual species of hardy plants. Just remember to plant things that don't need much water, grow slowly and stay small. You don't want to hide the stonework.

After all, a crevice garden is basically a dry stone wall laying on its side, buried flush to the ground.