Succulents can have many uses in the landscape. They often fill the role of ground covers. Those with rock gardens have many opportunities to use succulents.
Some of the ones mentioned below may be more suited to warm locations, while others are perfectly hardy in USDA zone 5.
For rock gardens, the best choices are those with a rosette form. However, yuccas and other vertically shaped ones like Euphorbias—especially the lower growing varieties—are good choices. So far as the actual species or cultivar are concerned, you’ll find many offered at retail garden centers as well as numerous listings in mail-order and on-line catalogs.
Among the hardy ones, those with rock gardens can choose from yucca, Sedums, Sempervivum, Euphorbias, and Delosperma.
Those in warm climates can choose from more tender species, including Crassulas, Aeoniums, Aloes, and Echeverias.
Suitable for zones 9 through 10, the Aloes are exquisite succulents. Quite a few species and cultivars of Aloe are available. In the North, these can only be grown as pot plants. The most widely known is the ordinary aloe (Aloe vera), which is used as a medicinal plant.
Of the Aloes, the dwarf ones are the best choice for rock gardens. The hedgehog aloe (Aloe humilis) is particularly lovely. Only about six inches in height, its gorgeous blue-green leaves form rosettes. The narrow foliage has white teeth along the edges. Unlike some succulents, this one will grow well in shade.
Two other low-growing species of Aloes are suitable for rock gardens. Aloe aristata doesn’t seem to have a common name other than aloe. Like the hedgehog, this one is less than a foot in height. The four-inch long foliage are toothed along the margins.
Aloe brevifolia is more robust than the ones I’ve already mentioned. It tends to form lots of suckers. The gray-green foliage is triangular to oblong.
For colder climates, the Sempervivum or houseleeks are an excellent choice for rock gardens. They are also known as live forever. These sun-loving succulents require a well-drained soil. Other than that, these plants aren’t fussy. As the plants mature they will produce pups. Once the mother plant blooms, it will die but the new offsets will replace it.
Sempervivum are becoming very popular. You shouldn’t have to look very far for some attractive, colorful varieties. In my area, local garden centers and nurseries offer every color and kind imaginable. There are numerous species, and most are hardy to zone 4 or 5. Depending on the kind you buy, the rosettes can be up to three or more inches across. Some will have colorful filaments.
These are native to colder areas of Europe, such as Russia and the Alps. The flower colors vary somewhat from one species to another. Typically, they’re red, yellow, or greenish.
One of the most attractive is the spiderweb houseleek (Sempervivum arachnoideum). Only about four inches tall, this is hardy for zone 5. As you might guess from the common name, this one has cobweb-like filaments. Its vivid red blossoms are an inch across.
Though many of the Echeverias are very tender and suitable for warm areas—zones only 9 and 10—there at least one species that grows as far north as zone 7. Typically, Echeveria harmsii is very common in southern California. This species is often used as a ground cover. It is also planted in masses for flower borders. This is a much-branched succulent with leaves that are near the ends of the branches. The vivid red blooms have a touch of yellow. These are about an inch in length. They appear either in pairs or singly towards the ends of the branches. This occurs during the summer months. All of these succulents would be great choices for rock gardens.