When we speak of listing "rock garden plants," we are not, of course, referring to a botanical classification. There are all kinds of possible entries for such a list, depending on your conditions and aesthetic goals. But that does not mean that your plant selection has to be random.
Nor does it mean that some specimens have not been favored as classic rock garden plants. These rockery classics tend to share certain characteristics, including:
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If you have just a small space in which to landscape, then it will probably make the most sense for you to select small rock garden plants. Luckily, the choices here are legion. There are many small rock garden plants whose delicate beauty is quite exquisite, such as purple ice plant (Delosperma cooperi), shown in the picture.
Keep in mind that features such as small stone retaining walls can also house rock garden plants. Small specimens such as hens and chicks are indispensable for planting the crevices in dry-wall stone walls. Meanwhile, bright-flowered, cascading beauties such as yellow alyssum are ideal for planting on top of walls, allowing them to spill down the sides. The effect of these plantings is to soften the otherwise rigid lines of the wall.
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Sometimes, like Goldilocks in the fairy tale, you are looking for that happy medium. You do not want anything too small, but something too big will not work, either. So in this section, we present some examples of medium-size rock garden plants.
One favorite is columbine; the shape of its flowers are fascinating. But there are plenty of other possibilities, among them coneflower (Echinacea), which, like columbine, is a North American wildflower. If you would like to mix things up a bit and inject some silver leaves, try rose campion (Lychnis coronaria), but keep an eye on it if you do not wish for it to spread.
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The next best thing to having the Hanging Gardens of Babylon in your yard is landscaping a steep slope with boulders and eye-catching rock garden plants. This is an example of turning what could be a landscaping nuisance into a highlight. But tiny specimens dotting a gigantic hillside will not show up very well—unless massed for a blanket-like effect, as we sometimes see on hillsides with creeping phlox), so you will have to turn to the big boys in these situations. Just remember that the idea is to keep everything in proportion, which is why we used the word "boulders" rather than "rocks."
One tough specimen of suitable size and useful in such conditions is Rosa rugosa. Another robust customer is rockspray cotoneaster. An evergreen selection and a nice choice for a Japanese theme is mugo pine.
Russian sage (Perovskia; pictured) and lamb's ear are more delicate-looking than the other members of this section, but they still offer some height where it is needed. In the latter case, however, the height is in the flower stalk; in fact, if you want to use lamb's ear as a smaller specimen, just remove the flower stalk when it appears and treat it as a foliage plant. It is a flowering ground cover that will spread.
What Makes This Landscaping Feature Special
The beauty of a well-planned rock garden is that the rocks and the plants work together, elevating the impact of both. Showy plants draw attention to the rocks, which, in turn, offer a delightful framework within which to show off your rock garden plants in their best light.