The Japanese rock garden is divided into three subcategories. The Tsukiyama is the hill garden, which represents nature sculpted by man. The Karesansui is the dry garden, in which the world is represented by abstract means. The Chaniwa is the tea garden, used for traditional tea ceremonies. Though the intent and exact landscaping materials may vary, rocks tend to be the anchor or mainstay of these themes.
As all Japanese rock gardens are intended to be viewed from a distance rather than interacted with, the scenery of the hill garden must be tailored to be aesthetically pleasing when viewed from a predetermined angle. Rather than land being the focus, water is. A central pond or stream meanders along, shrinking in width to provide a completely uninhibited view of its banks. It's inhabited by carp and half-submerged granite stones, with stepping stones set from one shore-side to the next and a few shoals of stones at the far end. At its edges willow, Japanese barberry, and winged euonymus hang over the water.
Further ashore, surrounded by Japanese sedge grass which is known for being vividly green and tidy, is the occasional flowering shrub like silver bell or pearl bush or tall Japanese pine.
At the furthest end of the pond, rising from the water and centered in the onlooker's field of view, is a mountain in miniature, composed of either raised earth carefully sodded or a shaped stone representing Fujiyama, the spiritual heart of Japan. From top to bottom, every blade of grass and living plant is pruned to have flat, rounded edges.
The dry garden is what is most commonly thought of when a Japanese rock garden is mentioned. No grass or other plants are used and straight lines are strictly avoided in their design. The landscape is composed primarily of sand, though gravel or volcanic sand might be used as an alternative. It's raked in concentric circles and whirls in order to represent the ocean. Amidst the sand is placed stones half sunken into the earth to represent mountains and occasional patches of moss indicative of dry land.
The key here is emptiness. By avoiding using much in the way of color and texture you shift focus from what is there to what is not there, which is the point of such gardens. In contrast to the intended flow, the outer boundaries of the garden are clearly discerned by cutting into the sod or using wooden slats set between sand and grass. Again, the boundaries must be rounded rather than straight-edged.
Traditional tea gardens are three dimensional as they are meant to provide a panorama from a tea house set in the middle of the garden. Seeing as building an entire tea house is rarely within the constraints of one's budget and available space, place the garden around a backyard pavilion or similar structure to achieve the same wrap-around view of nature.
Rather than a lowland theme, a tea garden might utilize a more mountainous theme. Surrounding the pavilion itself is a cut granite walkway which leads out to a series of stepping stones by which a guest might arrive. Fine gravel would surround the stepping stones and fern moss would comprise the groundcovering on the wayside. This would segue up into lichen-covered stones and dwarf evergreens like Hinoki cypress, Japanese cedar and Oriental spruce.
Finally, on the garden outskirts, hiding the pavilion from view, are full-size conifers like Japanese pine, umbrella pine, and Japanese maple. A nod toward traditional ornamentation would be a lichen-covered stone cistern and ladle for washing next to the pavilion steps.