Habit largely determines what rock plants, and where they can be placed. The tufted plants are the most distinct, forming rosettes of foliage with short flower stalks above. These are best suited for cliffs and tiny crevices. These include:
- Alpine Thrift (Statice montana )
- Tufted Saxifrage (Saxijraga caespitosa)
- Alpine Poppy (Papaver alpinum)
- Banded Pink (Dianthus zonatus)
- Smooth Alumroot (Heuchera glabra)
The next category is the dwarf erect plants of one foot in stature or less, these are relatives of border plants. These should be planted into large flat areas and tops of ledges, where they are above the creeping sorts, adding 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 category of drooping plants like to hang down over a rock face, growing in long streamers. Place these in the steep slopes near the top, but be careful because they smother any plants below them. They will crowd out smaller less hardy plants on flat spaces. This category creates the foliage bulk of 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)
There is also the category of drooping plants that have a 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 are perfect for covering tiny cracks in flat or sloping places, reaching across the stones after all the soil has been covered.These are good choices for carpeting in the walks, but this be careful not to let them spread into the pockets of the rare tufted kinds, as they will overpower them. 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)
This matted bed, allows liitle bulbs, like the Snowdrop and Squills, to push upwards blooming in spring against a background of foliage. When they dry away, there will be no patches of bare dirt above them thanks to these covering. Many types of plants are found in modern rock gardens, but some of are not suitable. It is often a good idea to place limitations on the amount of plants added.
Except for large rock planting or as special accent, a rock plant should be no more than a foot in height (or 30 cm) on the average. This restriction in height allows all the plants to remain in proportion with the setting. Plants that are used in a flower border or elsewhere about the lawn should not be used for a rock garden, where the idea is to create a mountain slope with exclusive vegetation.
This garden is a selective garden, and because it only houses small varieties, common garden plants should not be used. There are some weed-like plants that will grow very well in these conditions. 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. However, the only way to tell what is weed or not is to try them out.
Rock plants do best in full sun in poor sandy soil, either by means of deep root-system or fleshy stems and leaves. Plants that have special conditions, like moisture and shade, are not for the usual rock garden. There are plenty of plants that withstand the baking heat of any summer so long as their bed has been properly constructed.
When hunting for new plants for a rock bed, any little weed on the side of the hill is dragged in by its Latin name and pronounced beautiful. These weeds may be pretty, but they are often simply easy to grow, and there is no point in adding something that does not have pretty flowers or foliage to the garden. Weeds can seem a good alternative be however, to Primroses from Yunnan or Saxifrages from the Alps which seem unwilling to thrive on a manufactured mountain in a foreign soil and climate.