Often there are those areas of your garden that just aren't suitable for lawn or have exposed ledge and rocks making it impossible to plant shrubs. These areas can easily be transformed into beautiful rock gardens by rearranging of some of the stones and bringing in a bit of new soil. If you don't have enough stones add a few new ones. You can also start a rock garden from scratch on slopes which are too steep to mow. Since most plants which thrive in rock garden settings are sun loving try to pick the sunniest spot possible for your rock garden. If, however, your rocky slope happens to be in the shade there are a number of interesting ferns and woodland perennials which will do just fine.
A successful rock garden depends on the choice and arrangement of the stones and striking the right balance between the stones and plants. Choose stone with character, with interesting shapes and maybe some lichens or moss. When choosing new stone the most important thing to remember is the character of the existing stone back at the site. Try to use one type of stone throughout the garden. Keeping them consistent will result in a garden which seems to belong to the site. Also, stone native to your area will look natural, be inexpensive and easy to obtain. Large rocks with irregular shapes look interesting in the rock garden, but keep in mind that you'll need smaller rocks as well. Look for stones which have natural depressions in them, these can be filled with soil and planted with moss or succulents such sedum (a beautiful groundcover with yellow or pink flowers).
When arranging the stones in the rock garden let the site's natural conditions guide you. For example, if there are distinct characteristics common to the all the stone such as cracks or fissures arrange them so they all face in the same direction. If there's moss on each of the stones place them so the moss faces one direction. This will allow your garden to blend in with the surrounding landscape. If you are building a garden on a slope, fill in behind each stone as you work your way to the top and if possible, try to create relatively deep pockets of soil making suitable spots for a few small shrubs. Its also important to bury the stones about half way to make sure they're secure and stable. After the rocks are in place let the soil settle around them for a few days then take a look at the arrangement from a distance to be sure you like the layout before adding plants.
With the stone in place, its time to begin the process of choosing your plants. Low growing perennials such as creeping phlox, alyssum, thyme, thrift and speedwell work wonderfully in the rock garden. Where the soil is deep enough dwarf evergreens such as blue carpet junipers and dwarf hinoki cypress will add color to the garden throughout the winter. Since many of the plants best suited to rock gardens bloom only in the spring, consider incorporating a few annuals for color throughout the season. Though a rock garden can contain only those plants which grow naturally on rocky slopes in poor soil, proper maintenance allows for a wide variety of plants.
Though rock garden plants will generally do better in drier conditions and poorer soil than most plants, you should care for them as you would perennials. Fertilize in the spring along with your other gardens and make sure to water often, especially during the hot summer months, as the soil in rock gardens tend to be shallow and will quickly dry out. Just as with any perennial garden the soil should be occasionally cultivated and weeded. Never let weeds grow in the nooks and crannies, they will easily crowd out plants in small areas. If the weeds get too large in the more shallow pockets their root systems can spread throughout the entire area. If this happens pulling the weed will often remove the entire pocket of soil so try to avoid letting the weeds and grasses get out control. Most rock garden plants do well in poor soil, but the occasional addition of manure or compost will give them a boost. Also, just as in perennial gardens, maintenance should include cutting back any leggy plants after flowering, clipping off dead stems and foliage, and dividing any plants that become root-bound or too large for its space. Because plants in a rock garden are more exposed than plants in a level bed, they may need more protection in winter so heavy mulch should be applied late in the fall in cold climates.