A rock garden is a planting area designed with a hardscape that features a selection of gravels, rocks, and/or boulders; and typically it is planned to include certain softscape plants suitable to those conditions. In some areas, rock gardens are known as "rockeries" or "alpine gardens", since mountainous regions are known for having this kind of rocky terrain. 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 that shows off your rock garden plants in their best light.
So-called "rock garden plants" are not a botanical classification, but rather a group of plants that share certain characteristics, including drought resistance, a preference for good drainage, and a compact growth habit. While most rock gardens tend to be sunny gardens (mountain regions often lie above the tree line, after all), but there are all kinds of possible entries that depends on your conditions and aesthetic goals.
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Small Plants for Rock Gardens
If you have just a small space in which to landscape, then it probably makes sense to select small plants for your rock garden. There are many small plants whose delicate beauty is quite exquisite for rock gardens, such as purple ice plant, Delosperma cooperi, (pictured). An entire rock garden can be given over to small plants; or, you can use them in the foreground or as edging plants in a garden with plants of mixed sizes.
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 in the crevices of dry-wall stone walls. Meanwhile, bright-flowered, cascading beauties such as yellow alyssum are ideal for planting on the tops of walls, allowing them to spill down the sides. The effect of these plantings is to soften the otherwise rigid lines of the wall.
Some small rock garden plants are creepers, such as dragon's blood stonecrop. But certain creeping plants also come with some serious baggage. Ajuga, for example, can be invasive under some conditions. If you still decide to grow it, remove stray runners promptly.
- Yellow alyssum (Aurinia saxatilis): perennial in zones 3 to 7; sometimes grown as an annual in zones 8 to 10
- Purple ice plant (Delosperma spp.): a perennial succulent, hardy in USDA zones 5 to 9
- Angelina stonecrop (Sedum rupestre 'Angelina'): a perennial evergreen flower, hardy in USDA zones 5 to 8
- Dragon's blood stonecrop Sedum spurium): a semi-evergreen perennial hardy in USDA zones 4 to 9
- Hens and chicks (Sempervivum tectorum): a succulent evergreen perennial, hardy in USDA zones 3 to 11
- Creeping thyme (Thymus serpyllum): a creeping, woody-stemmed perennial herb, hardy in USDA zones 4 to 8
- Blue fescue ornamental grass (Festuca glauca): a short-lived perennial ornamental grass, hardy in USDA zones 4 to 8
- Snow-in-summer (Cerastium tomentosum): a perennial flower hardy in USDA zones 3 to 7
- Candytuft (Iberis sempervirens): a ground-hugging perennial flower, hardy in USDA zones 4 to 8
- Ajuga (Ajuga reptans): a perennial ground-cover flower that accepts partial shade, hardy in zones 3 to 10; may be invasive unless controlled
- Creeping phlox (Phlox subulata): a ground-hugging perennial flower, hardy in USDA zones 3 to 9
- Pasqueflower (Pulsatilla vulgaris): a perennial flower, hardy in USDA zones 4 to 8
- Reticulated iris (Iris reticulata): a perennial bulb, hardy in zones 5 to 9
- Wood spurge (Euphorbia amygdaloides): a perennial flower that accepts part shade, hardy in USDA zones 6 to 8
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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.
Among the plants of medium size, one favorite is columbine (Aquilegia); an alpine native with flowers that are fascinating in shape. 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. Good options for medium-sized plants include:
- Moonbeam coreopsis (Coreopsis verticillata 'Moonbeam'): a perennial flower in the aster family, hardy in USDA zones 3 to 9
- Lavender (Lavandula spp.): herbaceous perennial flower, hardy in USDA zones 5 to 9
- Yarrow (Achillea millefolium): a flowering perennial, hardy in USDA zones 3 to 9
- Autumn Joy sedum (Hylotelephium 'Herbstfreude' Autumn Joy): a fleshy-leaved perennial flowe,r hardy in USDA zones 3 to 9
- Royal Candles speedwell (Veronica spicata'Royal Candles.'): a compact perennial flower, hardy in USDA zones 3 to 9
- Columbine (Aquilegia spp): a perennial wildflower with many cultivars, hardy in zones 3 to 9
- Coneflower (Echinacea spp.): a daisy-like perennial, hardy in USDA zones 3 to 9
- Purple fountain grass (Pennisetum setaceum Rubrum): an ornamental grass that is hardy in zones 9 to 11, but used as an annual elsewhere
- Blue Rug juniper (Juniperus horizontalis 'Wiltonii'): a ground-hugging needled evergreen, hardy in USDA zones 3 to 9
- Shasta daisy (Leucanthemum x superbum): an easy-care perennial flower, hardy in USDA zones 5 to 9
- Black-eyed susan (Ruudbeckia hirta): a daisy-like perennial flower, hardy in USDA zones 3 to 7
- Perennial salvias (Salvia spp.): most are woody-stemmed perennial flowers; hardiness zone varies according to species
- Six Hills Giant catmint (Nepata 'Six Hills Giant'): an aromatic perennial flower, hardy in USDA zones 4 to 7
- Rose campion (Lychnis coronaria): a clump-forming perennial flower, hardy in USDA zones 4 to 8
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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 one example of turning 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.
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.
- Mugo pine (Pinus mugo): a moderately low-growing, spreading needled evergreen shrub, hardy in USDA zones 3 to 7
- Russian sage (Perovskia atriplicifolia): a flowering perennial with shrubby, woody stems, hardy in USDA zones 5 to 9
- Rockspray cotoneaster (Cotoneaster horizontalis): a flowering deciduous shrub with reddish leaves and bright red berries, hardy in USDA zones 5 to 7
- Lamb's ear (Stachys byzantina): an herbaceous perennial grown for the texture of its leaves, hardy in USDA zones 4 to 7
- Maiden grass (Miscanthus sinensis 'Gracillimus'): a perennial ornamental grass with good drought tolerance, hardy in USDA zones 5 to 9
- Rugosa rose (Rosa rugosa): a sprawling, thorny flower shrub, hardy in USDA zones 3 to 9, may become invasive