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Water-Thrifty Rockroses
By Neil Bell
Rockroses (Cistus spp.) and their close relations in the
genus Halimium are evergreen shrubs in the cistus family (Cistaceae).
Their native range stretches from the Canary Islands in the Atlantic
Ocean through the Mediterranean basin to the Caucasus Mountains of
eastern Europe, but rockroses and halimiums have become popular in other
regions that have Mediterranean-style climates. Their evergreen,
aromatic foliage and showy flowers are welcome benefits for the
challenging sites where rockroses thrive. Because of their tolerance of
poor soil and drought, rockroses perform reliably growing along dry
banks, parking lot islands, and other locations where water is a
limiting factor and many common landscape plants struggle. They are also
resistant to browsing by deer and other herbivores.
Like other shrubs of Mediterranean origin, Cistus and
Halimium species have evolved in regions that experience hot, dry
summers and winters that are wet but not excessively cold. This matches
the climate along the West Coast of North America, so it is gardeners
from southern California through western Oregon and Washington to
southwestern British Columbia who have become most familiar with these
plants. Most of the species are hardy to USDA Zone 8 or 9 and heat
tolerant to AHS Zone 10. They are rated for Sunset zones 6 to 9 and 14
to 24.
 Yet
most of the Cistus and Halimium species and cultivars that exist
worldwide are unknown in North America or are being grown only by
enthusiasts. The Cistus most commonly used in landscaping on the West
Coast are C. 5hybridus, C. 5purpureus, and C. ladanifer. The genus
Halimium is even less commonly used; if a gardener can find one at all,
it is most likely to be H. lasianthum.
However, availability of new cultivars of both genera has
increased recently due to an interest in and - in some regions - an
outright need for water-thrifty landscape plants. Gardeners who are only
familiar with the commonly-grown selections will be surprised at the
diversity of size, form, foliage, and flowers within each of these
genera. Given this and their tolerance of drought, it’s worth having a
closer look at what these plants offer the dry garden.
General Characteristics
Rockroses range from small (two to four feet tall) to
large (six to eight feet tall) with forms that can be prostrate,
mounding, or upright. All have opposite leaves, which may be mid- to
dark green or, very commonly, grayish. The flowers are distinctive,
having delicate, often crinkled petals that usually drop after being
open a few hours. The following morning, a new set of flowers will open,
so the flower show continues for two to three weeks, and sporadically
for much longer in some cases. The primary flowering time for most
species is between April and late June, depending on region.
The flowers of both genera are unscented; in Cistus they
are usually white, pink, or purplish, while in Halimium they are
commonly yellow or white. Some may have a spot at the base of each
petal. The spent flowers develop into reddish or dark brown capsules,
which split open to reveal numerous, small, dark brown or blackish
seeds.…”
Rockroses
Cistus is derived from the Greek word kisthos or kistos,
which were the classical names for various species. These days they are
commonly known as rockroses, based on the resemblance of the flowers to
old-fashioned, single roses—and on the preferred habitat of the plants,
which is rocky, relatively poor soil.…
There are about 70 hybrid species and cultivars in cultivation. In North
America, the best known selection is probably C. x purpureus, a hybrid
of C. creticus and C. ladanifer that grows four feet tall and six feet
across. Its pink flowers have a distinctive dark red blotch at the base
of each petal. Another commonly used species is C. x hybridus (C.
populifolius x C. salviifolius) a rounded shrub that grows to four feet
high and six or more feet across and has unblotched white flowers.
‘Sunset’, a selection of C. x pulverulentus, has a very compact habit,
growing only two feet tall and three feet wide with gray-green foliage
and magenta flowers. Also low-growing, to two or three feet, is ‘Mallorca’,
a selection of C. ladanifer var. sulcatus introduced by Sean Hogan of
Cistus Nursery in Sauvie Island, Oregon.
Halimium
The seven Halimium species currently recognized originate
from southern Europe - especially Spain, Portugal, and France - and
North Africa. Two species, H. halimifolium and H. lasianthum, have a
reddish or dark brown flower blotch and have passed this trait along to
certain selections.…
Halimium can be divided into white- and yellow-flowered
species. The single white-flowered species is H. umbellatum, a dwarf
plant growing only 18 inches tall but spreading to four feet or more.
The best known species, H. lasianthum, features silvery foliage and
yellow flowers that often have a dark blotch on each petal. Horn
describes it as drought tolerant and “undeterred by the cold weather” of
this past winter. Halimium ocymoides is a low, spreading plant that has
blotched yellow flowers opening from red buds. H. calycinum, another
low-growing species, has unblotched yellow flowers.…
Design and Companion Plants
Rockroses are most effective when used as components of a
landscape that requires very little water and are best paired with
plants similarly tolerant of drought. Simply plopping rockroses in among
thirsty shrubs or perennials often produces a flush of unwanted growth
and predisposes them to fungal diseases. “A common mistake is to place
them within range of the sprinkler system,” says Hogan.
Rockroses are not fond of repeated shearing or other forms of hard
pruning either, so it’s best to site them where they can be allowed to
grow to their mature size with minimal shaping.…
Photo credits: Cistus ‘Snow Fire’ by Catriona T. Erler.
Cistus x purpureus by Saxon Holt..
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