Rock garden plants tend to be small, both because many of the species are naturally small, and so as not to cover up the rocks. They may be grown in troughs (containers), or in the ground. The plants will usually be types that prefer well-drained soil and less water.
The usual form of a rock garden is a pile of rocks, large and small, esthetically arranged, and with small gaps between, where the plants will be rooted. Some rock gardens incorporate bonsai.