Ideally, a rock garden should in some way resemble a natural rock outcropping. This is not always possible because of a lack of rocks, absence of a slope or not enough money in the budget.

The most common type of rock garden in the temperate zones is the alpine garden. As the name implies, this is supposed to mirror a piece of the Alps Mountains. That means large rocks jutting out from the earth and the use of alpine plants. Otherwise, it will look out of place.

Such plants have a very short bloom period. In the true Alps, the snow melts away about early summer and in a month or two falls again. These plants have to get out of the ground, flower and set seed quickly. For most of us gardeners, having one of our gardens in flower for only a month in the spring would not be acceptable. So, we tend to bend the rules a bit and include other, non-alpine, type plants.

If your landscape is completely flat, it will be difficult and, probably expensive, to build a true alpine garden. Sloping ground or, even better, an actual hill would be the desireable locations for the rock garden.

Most of us will not have much of an option for the location. In a small, urban-suburban site, you will have to make the best of what your property presents. Unfortunately, some sites just won't allow for construction of a rock garden that looks "natural".

If your site just doesn't allow for the naturalized approach, you can try using a more formal tone. Use flagstones and stone terraces to simulate a small section of a true rock garden. However, this should only be used if you have no alternative (IMO)

The ideal site would be facing to the south or southeast so that it can warm up earlier in the spring and get the alpine plants off to a good start. That is the type of environment they come from where they must get going at the first hint of warm weather. Most of these plants are pretty tough and can withstand a few spring frosts.

The selection of the rock and other materials to use in this type of garden is very much the key to success. The plants will always do their part but the backdrop and atmosphere that creates the feel of the garden will rest on your rock selection.

Typical types of rocks used include sandstone, limestone, granite, tufa and pumice. Roundish field stones may be used but the garden will not be as effective as it would be with larger, slab-like rocks.

Here are a few guidelines to consider when choosing your materials:

1. The rock should be of a type common to the local area. In any particular area, there is usually a dominant local rock such sandstone. Your garden will fit into the surroundings and look more like it really belongs if it reflects the common materials of the region.
   
   

2. Use only one type of rock, if possible. Again, in most small areas such as your landscape, you would only find one type of rock. By mixing two or three types into one garden, it will give the viewer more of a feeling that it does not fit.
   
   

3. Obtain it all from one source. Most rock has certain colors and textures and you are more likely to have all the rock match if you buy it from one supplier. Again, this will contribute to the natural look of the rock garden.
   
   

4. Use some extra rock in the surrounding area. Another way to make the rock garden seem realistic is to place a few pieces of rock in nearby beds and borders. Just like you carry a certain color shade through the garden, you should carry the impact of the rock out in the nearby landscape too.

Alpine or rock garden plants generally fall into the same category as rhododendrons when it comes to soils. The key is that they need a well drained soil that also holds enough moisture for their needs.

In mountainous areas, the soils are usually quite coarse with plenty larger particles of rock involved. This gives them the great drainage needed by alpine plants. However, there needs to be a certain amount of organic matter mixed in so that the soils will hold on to some of the water and the nutrients as they pass through.

Rock gardening involves planting things in the cracks and crevices between the rocks. So, these areas need to be supplied with a mixture of soil, organic matter and something coarse like pea stone.

Level off the various "shelves" created by the rocks so that rain will penetrate down through the soil rather than runoff and cause erosion.

The vast majority of the plants you will use prefer a slightly acid soil in the pH 6.0 range. Unless you know that your plants require and alkaline soil, a low pH number should be the goal. Garden sulfur and aluminum sulfate may be used to make soils more acid if needed. Lime will raise the pH and make the soil more alkaline. Either way, get a soil test so you know the needs of the soil. Don't just guess!

Consider the following when actually placing your rocks to form the garden:

1. Make a good foundation. Be sure to start with level, flat positions for placing the rocks. A little forethought and preparation before you start moving the rocks will certainly pay off in the long run.
   
   
2. Arrange the rocks as if they are emerging from the ground. Bury up to half of the rock under the soil to appear as if they are being thrust out of the earth by some prehistoric shift. Take some time with the placement of the rocks and don't just scatter them around randomly.
   
   
3. Tilt the rocks slightly to the back. This will accomplish two things. First, it will encourage water to run off the rock and toward the area where the plants live. Second, it will make the stone appear as if it is rising out of the ground in nature.
   
   
4. Put the best rocks on top. Be sure to align the "grain" of the rock piece in the same direction. Inspect the rocks and set aside those that should be in the top layer that is exposed to the viewer. Rocks with blemishes or structural faults should be placed below the other rocks or where they will not be prominent.
   
   
5. Built plant containers. Remember that the purpose of this construction is to provide places were plants can grow surrounded by stone. Be sure to leave cavities and openings where soil can be placed and plants may be grown.

The key to selecting plants for the rock garden is to find species that are true alpine plants from mountainous regions or plants that are small and delicate regardless of their point of origin.

The types of plants to use in a rock garden would include:

1. Herbaceous Perennials - These will be the largest group of plants used in most rock gardens. Of course, they should come back year after year and begin to spread to eventually look naturalized.

2. Bulbs - Many bulb plants are well adapted to a rock garden situation. Of course, in keeping things in the proper perspective, you should use ones that are naturally small or dwarf varieties of other types.

3. Evergreen Shrubs - Dwarf shrubs and small evergreens are an essential part of any rock garden. They introduce accents and contrasts as well as providing a background for the garden itself. A rock garden is an attempt to reproduce a mountain scene in miniature; the selection of suitable woody plants is therefore somewhat restricted. However, the following lists should offer a reasonably good choice to give variety to the rock garden.

4. Deciduous Shrubs - Only shrubs of dwarf habit are suitable for the rock garden and even then they will be suitable for the less confining site.

5.Trees - Certain small trees can be effectively used in a rock garden site. Often those with a cascading canopy will give the effect of a waterfall or stream.