When I started with my first cuttings of C. ladanifer ten years ago, there were only a handful of species and hybrids commercially available. Nowadays, rock roses are gaining popularity with gardeners as valuable xeriscaping plants, especially on the West Coast, where water issues are becoming increasingly more important. They are excellent plants for dry gardens, silver gardens, and large rock gardens. Some species have such extensive root systems that they are used in California for stabilizing the soil on dry banks. Also, where wildfires pose a problem, these resinous plants are an excellent choice for their natural fire-retardant attributes.
Many plant breeders are using C. ladanifer to develop new hybrids. (C. ladanifer is the only species with a blotched flower, so any plant that has a blotch has C. ladanifer as a parent). Breeding has expanded the range of flower color and size, leaf color and texture, and the variety of growth habits, from dwarf, spreading shrubs to large, tall specimens.
In the garden or landscape, I generally recommend mass plantings when using the small to medium Cistus species. This gives the plants more presence in the garden and multiplies their fragrance. The lower-growing C. ¥corbariensis or C. ¥skanbergii tend to be compact, dense spreaders about 3 or 4 feet across. They may also prevent fire (although less resinous) and soil erosion. The medium-height species, such as C. crispus, C. parviflorus, and C. libanotis, are more open and wild-looking, so they look best planted together in a more informal garden. For single specimens, I use the hybrids, especially C. ¥purpureus cultivars with their different foliage and flower colors and textures. Recently, I have seen highway and urban plantings of rock roses, which testifies to their plant hardiness and drought tolerance.
Between my greenhouses, I have two 100-foot-long perennial borders where my rock roses thrive. This area is sheltered from cold winter winds and has full sun exposure with additional reflected light and warmth from the greenhouses. At the end of one border, I had a pile of horticultural pumice. I raked it out and planted my yellow rock rose Halimium lasianthum) and ¥Halimiocistus wintonensis ‘Merrist Wood Cream’; the pumice makes the soil porous and free-draining, and the white color reflects light into the bush. The rock roses that are planted further down the borders are in a heavier soil, mulched to add organic matter and control weeds. It is much more acidic than their native habitat, yet they all do very well in it.
My borders are large, informal beds hosting stock plants for the nursery, and rock roses fit right in. My favorite, C. ladanifer, gets quite large and rangy and dominates the back of the border with its mass of flowers and foliage. In the heat of the summer, the plant exudes more resin, and the leaves become so sticky they actually glisten in the sun. This added protective covering helps minimize desiccation from both wind and summer heat. In wintertime, as the temperature gets colder, the leaves of C. ladanifer and C. ¥cyprius take on a pewter-silver color, which is quite unusual and attractive. C. ladanifer easily stands alone as a specimen planting, but I like the more compact C. incanus ssp. creticus with its wavy silver leaves and pink flowers in mass for full effect. The rock roses are heavy bloomers, but none more so than C. ¥corbariensis. The bright-red buds open to reveal a shower of 1-inch dainty white flowers. Without hesistation, I love the Halimium and Halimiocistus hybrids for their flower colors, especially the yellow Halimium lasianthum and the exciting canary yellow ¥Halimiocistus wintonensis ‘Merrist Wood Cream’. These plants make excellent evergreen rockery shrubs as they grow about 11/2 to 2 feet tall but get much wider in spread, spilling their gray leaves over the rocks. They are just as happy in full sun as the Cistus and are just as hardy. Give them added drainage by amending the soil with horticultural pumice.
I usually purchase new rock roses as 4-inch plants from nurseries or by mail order. I pot them up in 1-gallon containers until they’re big enough to go out in the garden. I find they are good candidates for container growing—especially if the winters are too cold to grow them outdoors year round. I particularly like C. ¥purpureus ‘Alan Fradd’ as a container plant with its white flowers with a purple blotch and its fine-textured foliage. Because of its compact form, it would do quite nicely on a terrace, patio, or other confined area within the city.
Having grown rock roses for so long, I cannot envision my border and herb gardens without them. They blend well with my other Mediterranean herbs such as lavender and rosemary. Their long succession of very showy flowers and interesting leaves are welcome in the herb garden.
Rock Rose Sources
Crimson Sage Nursery
PO Box 337
Colton, OR 97017
7530 NE 288th St.
Kingston, WA 98346
Joy Creek Nursery
20300 NW Watson Rd.
Scappoose, OR 97056
Click here for the main article, Rock Roses.
Andy Van Hevelingen is a frequent contributor to The Herb Companion and enjoys writing, photography, and gardening in his Newberg, Oregon, home.