A rock garden mimics the natural look of a rocky mountain slope or outcropping of rocks dotted with dwarf and creeping plants that thrive in the freely draining conditions. You can make a rock garden as small or large as you like, according to the available space and your budget, but a small, simple garden is probably best for a beginner.
Selecting a Site
Slopes and uneven ground provide the best sites for rock gardens, but you can also create one on flat ground. A rock garden should be sloping or uneven to encourage rainwater to flow quickly away and avoid waterlogging the rock garden's plants. Create an uneven structure by using existing sloping or uneven landscape or by raising part of a flat area with stacked removed turf. A rock garden on a flat site should have a layer of coarse stones on its base to provide drainage.
Select an area for your rock garden that receives at least four hours of direct sunlight every day. Many rock garden plants grow best when they receive six or more hours of sunlight daily, but many thrive on less.
A rock garden should not look too out of place in the natural landscape. Selecting rocks that occur naturally in your area will help achieve the correct appearance, and weathered and lichen-covered rocks also look naturalistic. Use the same kind of rocks for all or most of your rock garden, and select rocks of various sizes to add interest.
A small rock garden on a flat area needs at least three base boulders 2 to 3 feet wide at their widest points to provide the main structure over the underlying turf. Large boulders look impressive on a slope or uneven site, but five or six smaller rocks may be enough to create a rocky effect.
A rock garden's rocks must be placed carefully to provide a natural effect and for safety. Rocks with a grain should be placed so that the grain faces the same way for all the rocks. For safety, place the largest rocks at the bottom of a slope and smaller rocks above and at the top of a slope. Place each rock's broadest side downward for stability.
Building a Rock Garden
Dig a hole one-third as deep as the tallest base boulder you will use. If you create a rock garden on flat ground, then make the hole 3 to 4 inches deeper, and spread a layer of coarse stones 3 to 4 inches deep. Pile turf 2 to 3 feet deep over one-third of the rock garden base if the ground is flat.
Place base boulders that are 2 to 3 feet wide in the hole. Set the rocks so their weathered sides face upward if it is safe to do so. Base boulders provide a natural, interesting design with varying levels.
Pack soil in the gaps around the bottom of the base boulders, making the boulders stable and firm.
Place five or more smaller rocks on top of the base boulders. Arrange them so that small gaps and pockets where plants can grow are between rocks and so rainwater will flow toward those spaces.
Mix 1 part topsoil with 1 part sand and 1 part compost, leaf mold or other organic matter. Pack the mixture into the gaps and pockets between rocks.