"Instead of placing rocks into the soil berms (mounds of soil) from the side like stepping stones up the side of a hill, [the Czechs] use flat stones (such as pieces of flagstone or slate) that are pushed down into the soil vertically from the top. These vertical pieces are closely spaced leaving deep, narrow channels of soil...Additional information at High Country Gardens. I took the photo last week at the University of Wisconsin's Allen Centennial Gardens, a free public garden designed to demonstrate examples of gardening and landscape techniques.
Crevice gardens are especially good for growing cold hardy cacti, South African succulents and other xeric plants whose roots are sensitive to wet soil conditions. This is also a great way to grow larger growing xeric (low water plants) like Hummingbird Mint (Agastache), Lavender (Lavandula), Sundance Daisy (Hymenoxys), Beardtongue (Penstemon) and native Sage (Salvia) in moister climates. Just make a berm using a well drained soil mix. Bury some big flat rocks close together to create a vertical pocket crevice and plant."