I suppose the very best of rock gardens are created within a natural slope or rock outcropping. Unfortunately most of us will not be so lucky to have this natural habitat within our garden so we must recreate it the best we can. Since some of the best plants for rock gardens are alpines, it will be important that you choose a sunny site.
Planting a rock garden under trees should be avoided as the tree roots may be damaged. When planting a rock garden choose a site that is free of weeds, especially perennial grasses. Dig over the soil and add sufficient grit or sand to ensure good drainage for your plants.
Your choice of rock is very important for the end result appearance of your rock garden. Featureless rocks should be avoided as well as those that weather poorly. Select hard rock with good lines and character such as limestones and sandstones. Visit your local quarry or stone seller where you should be able to select the rocks you want. A few larger rocks will ultimately be more effective than many smaller rocks.
When your rock is delivered have it placed where you want it to stay, rocks are very heavy and moving can be almost impossible. Practice safety and protection when working with large rocks. Settle the largest rocks into their permanent position then add the smaller ones . Partially bury the rocks and expose their largest surface towards the front of the garden. This will create larger pockets for planting behind the rocks. Create elevations by building gentle slopes or mounds and position rocks to make it as natural looking as possible. Rocks with lichen or moss growing on them are a bonus.
Since you will be planting mostly alpine plants it’s a good idea to mix a pile of alpine garden compost for planting your alpines in. Combine one part loam, two parts potting grit or sand, one part peat and bonemeal. This will give you a soil mix with good drainage which is what most alpine plants require.
Alpines are those plants that grow on the mountain rocks above the tree line. They usually are from habitats that are harsh and exposed. For gardening purposes any small plants that are hardy will make adequate rock garden plants. Most alpine rock garden plants plants are perennials and are long lived. Your local nurseries will probably have many alpine plants to choose from.
Some are cushion forming where the flowers are well above the foliage on tall stalks. Others form a tuft or a mat which creeps outward from a center. You will also find small alpine shrubs such as dwarf willows, roses and junipers. Many alpines bear colorful flowers and by planting a mixture you can create an interesting tapestry of blooms.
Your rock garden or rockery looks especially nice next to lawns or a pool or stream. Keep your plants trimmed and de-headed after flowering for a neat appearance and to discourage too much self seeding.