This form of gardening that originated in England conjures an image of rocks combined with plants often on a slope. The slope itself can be naturally occurring or constructed, just as the stones can be natural outcroppings or brought in. Generally, the effect is one of plant material cascading down an incline of some degree with rocks holding the embankment in place and setting off the individual character of each plant. The alternative to this "natural" look, when a change in elevation is the case, is constructing retaining walls and/or terraces that look more formal by comparison.

What Kind of Rocks To Use:
The goal is to make your rock garden look as natural as possible, which is why larger stones are preferable. A lot of small rocks can look messy and ineffective. Try to work with stone from your area that will harmonize with your architecture and hard landscaping. All the rocks should be of the same general kind rather than a geological collection. Novelty rocks simply grab too much attention. Weathered stone that's porous is ideal. Limestone, for example, absorbs moisture and acts as a buffer during dry spells. Non-porous rocks such as granite can cause rapid drying of the surrounding soil system because it doesn't absorb moisture. Avoid all soft and scaly rock, shale, and unweathered sandstone.

How To Build:
When positioning stones on a slope try to imagine how they would look in their natural state. Avoid symmetry. A careful randomness is the look you desire. Arrange each rock so its best "face" will show well and then dig it a third to a half into the incline so it looks like an outcropping not a stone sitting awkwardly on top of the soil. Slope the stone back to direct rain towards plant roots. Vary the size of the planting pockets between the rocks to accommodate the various mature diameters of your favourite plants and to reinforce the idea of randomness.
Rock garden plants grow best in well-drained soil. After placing the stones, add a mixture of perlite, vermiculite, and peat moss into the planting pockets. Avoid rich soil or clay that won't drain. A sprinkling of lime is recommended in areas with acid-type soils. Two plant exceptions are Lithodora and Gentians that prefer the acidic soil condition. If your rock garden is going to be more than 2.5 m (8') wide, incorporate a path and/or steps through it so you can maintain plants, weed, and clean up in the fall.

What To Plant:
Your choice of plant material always depends on sun/shade conditions but proportion is key here in relation to the size of the rocks or boulders you're using.

If you're fortunate to be using large scale landscape rocks with approximately 100 cm (40") between them, you can work successfully with such slow-growing specimens as Rose Daphne, Nest Spruce, Dwarf Alberta Spruce, Boxwood, Little Giant Globe Cedar, Goldmound and Goldflame Spirea, Dwarf Hinoki False Cypress, Jeddeloh Dwarf Hemlock, Blue Star and Goldstar Juniper, Nikko Slender Deutzia, Dwarf Mugho Pine, Sunburst Hypericum, Dwarf Balsam Fir, and Red Ace, Yellow Gem, and Abbotswood Potentilla. These forms can be used with cascading plants like Dwarf Japanese Garden, Blue Chip, and Prince of Wales Juniper, Siberian Cypress, Rockspray Cotoneaster, Stephanandra, Wintercreeper Euonymus, and weeping Japanese Maple. By mixing evergreen with deciduous and vertical with horizontal you will create a tapestry of textures worthy of attention all year.
On a diminished scale, using smaller stones, miniature bulbs, annuals, and perennials would provide flowering interest for many months. You could start with spring-flowering bulbs such as Snowdrops, Winter Aconites, Glory of the Snow, Crocus, Iris reticulata, Puschkinia, Scilla, Dwarf Daffodils, and Greigii, Kaufmanniana, and species Tulips. For April/May there are many low-growing perennials that would add bursts of colour like Primula, Basket-of-Gold, Pasque-flower, Candytuft, Rock Cress, Creeping Phlox, Dwarf Iris, and Thrift. The next perennials to bloom are Woolly Yarrow, Mt. Atlas Daisy, Carpathian and Serbian Bellflowers, Creeping Speedwell, Yellow Ice Plant, Dwarf Dianthus, and Saxifrage. For summer you can intersperse annuals that will reliably bloom all summer. Dahlberg and Swan River Daisy, Alyssum, Lobelia, Portulaca, and Nierembergia are easily maintained. Summer-flowering perennials include Sun Rose, Coral Bells, St. John's-Wort, Blue Flax, and Stonecrop.
For a low mat effect, plant Creeping Thyme or Scotch and Irish Moss. For interesting foliage colour try Silver Mound or Silver Brocade Artemisia, bright yellow Creeping Jenny, black Lilyturf, Variegated Liriope, steel blue Donkey-tail Spurge, burgundy Bertram Anderson or Vera Jameson Stonecrop, or Elijah Blue Fescue.

Alpine Plants:
The terms "rock garden" and "alpine" plants are used interchangeably but a true Alpine grows above the tree line in mountainous regions. Alpine perennials, for example, have a dwarf habit, bloom profusely, and prefer a well-drained, gritty soil. True descendants of these Alpines include Gentians, Saxifrage, Alpine Lady's Mantle, Stonecrop, Edelweiss, Alpine Columbine, Lewisia, Alpine Poppy, Arctic Campion, and Alpine Aster.

Trough Gardens:
One way to create a miniature rock garden in a limited space is in a special planting container called a trough. They are most often a heavy rectangular tray with drainage holes that's elevated on concrete blocks and filled with a layer of stone at the bottom and quick-draining, gritty soil. A standard soil mix for a trough is 20% compost, 30% loam, and 50% fine gravel/sand. In a smaller trough, for instance, you could try planting succulent perennials like Stonecrops, Hens and Chicks, and Saxifrage with interesting rocks and gravel to finish the top. Very slow-growing evergreens can be used in larger troughs. Once planted keep the trough free of weeds and water as needed (every day or 2 in hot weather). Troughs with winter hardy plants can stay where they are or be set on the ground in December and covered with evergreen boughs.