From habit of growth there are several types of rock plants and their position is decided largely by their habit. Most distinct are the tufted plants, forming rosettes of foliage with short flower stalks above. These are for cliffs and tiny crevices, perfect for wall fountains, and are the alpine vegetation. These include:

• Alpine Thrift (Statice montana )
• Tufted Saxifrage (Saxijraga caespitosa)
• Alpine Poppy (Papaver alpinum)
• Banded Pink (Dianthus zonatus)
• Smooth Alumroot (Heuchera glabra)

Next there are dwarf erect plants of one foot in stature or less, small relatives of border plants. These are for the large flat areas and tops of ledges, where they are above the creeping sorts. These give height to the plantings. Try the following plants in this area:

• Rock Aster ( Aster alpinus)
• Alpine Columbine (Aquilegia alpina)
• Yellow Pink (Dianthus knappii)
• Harebell (Campanula rotundifolia)
• Mountain Phlox (Phlox ovata)

The drooping plants prefer to hang down over a rock face, growing in long streamers. These are best in the steep slopes near the top, though they smother any plants below them. On flat areas they soon crowd out smaller and less vigorous sorts. These are the plants that give foliage bulk to the rock garden and may be depended on to give the planting an effect of luxuriance, covering all blank spaces and even making the stones disappear in a sea of foliage. Examples include:

• Goldentuft (Alyssum saxatile)
• Snow-in-Summer (Cerastium tomentosum)
• Evergreen Candytuft (Iberis setnpervirens)
• Moss Phlox (Phlox subulata)
• Carpathian Bellflower (Campanula carpatica)

These are examples of drooping plants of very vigorous growth. The creeping sorts form close mats on the ground, rooting at the joints and covering the soil completely to a depth of a few inches. These fill in all tiny cracks in flat or sloping places, reaching across the stones after all the soil has been covered. For carpeting in the walks these are very useful, but this may not be sufficient domain and they clamber into the pockets and overwhelm the rare tufted kinds. Commonly used vigorous and crowding creeping plants include:

• Common Speedwell (Veronica officinalis)
• Maiden Pink (Dianthus deltoides)
• Creeping Phlox ( Phlox stolonifera)
• Mother-of-thyme (Tkymus serpyllum)
• Stringy Stonecrop (Sedum sarmentosum)

Through such matted plants as these the little bulbs, such as Snowdrop and Squills, will push their way and bloom in spring against a background of foliage. When they dry away, there will be no patches of bare dirt above them. All kinds of plants may be found in a modern rock garden, but some of them are hardly suitable. It might be well to put certain limitations upon what may be called a rock plant.

Except in very large rock plantings or as special accent, a rock plant should not be more than a foot in height (or 30 cm) on the average. This restriction in height is necessary to keep the plants in scale with the scenery. Plants commonly seen in the flower border or elsewhere about the lawn should surely be omitted from the rock garden if the notion that this is a mountain slope with exclusive vegetation is to be maintained.

Since this area is dedicated to plants too small or slender to be grown in the usual garden, the common garden plants should be kept out. But some plants, though small, are very much like weeds and grow far too well in the rock garden. Dandelion and Chickweed are persistent pests here, but no better are many others sold as rock plants. They are too troublesome as neighbors to better rock plants. There is no way to discover which ones are weeds except through trial.

Rock plants should thrive in full sun in poor sandy soil, either by means of deep root-system or fleshy stems and leaves. Those herbs, which demand shade, moisture, or other special conditions, are not for the usual rock garden. There are plenty of plants which will survive the baking heat of any summer if their bed has been properly constructed. Of extreme importance as a character of a good rock plant is interest in flower, foliage, or habit of growth.

In the hunt for more and newer rock plants any little weed on the side of the hill is dragged in by its Latin name and pronounced beautiful. There is no sense in cultivating tiny plants of little show in flower or foliage effect; yet many of such are extremely easy to grow, while Primroses from Yunnan or Saxifrages from the Alps seem most unwilling to thrive on a manufactured mountain in a foreign soil and climate.