Answer: First off, you should run some basic soil tests to determine the state of your soil. Your County Agricultural Extension office can help you with the tests and interpreting the results in view of what you want to grow. They may also have some suggestions for plants that do particularly well in your area. In general rock garden plants require extremely good drainage. Although your soil is clay, on a steep slope the drainage should already be good, and the soil may in fact be quite dry. Here are some possibilities: shrubs such as junipers (available in many sizes and heights and needle colors), dwarf barberries and cotoneaster, herbs such as creeping thyme, sage and oregano, perennials such as the many forms of sedum, various dianthus, salvias, purple coneflowers, Russian sage, and creeping phlox. You may have to improve the soil somewhat with compost to get the best performance from this list. There are also companies that specialize in rock garden plants, including succulents and alpines, which should do well with little or no improvement of the soil:
To read more about alpine and rock garden plants, visit the North American Rock Garden Society Web site at http://www.nargs.org/. Enjoy your project!
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