last several years, together with my OSU Master Gardeners, I have evaluated
species and cultivars of ceanothus, cistus and halimium for adaptability to
western Oregon gardens. Ceanothus is primarily a western U.S. genus, though
they are best known by the species and selections native to California.
However, there are ceanothus found through the midwest to the east coast,
principally Ceanothus americanus, a deciduous species that figures prominently in some
of the desirable hybrids. Cistus and halimium (and the hybrid between them:
Mediterranean in origin, ranging from the Canary Islands through the
Mediterranean basin to the Caucasus Mountains.
These trials are simple evaluations of
growth, flowering and cold hardiness conducted on plants grown in the open. No
special soil preparation or other techniques are used, so they are grown in
much the same way as a gardener would. The ceanothus trial was conducted at The Oregon Garden in
Silverton, Oregon between 2001 and 2005. The cistus and halimium were evaluated
at the OSU North Willamette Research and Extension Center, near Aurora, Oregon,
from 2004 through 2006. In both cases, the young plants were irrigated only for
the first summer until they were established. After that, no irrigation,
fertilizing or pruning was done on the plants. Cold hardiness was evaluated in
spring by assessing damage from the previous winter. The only real cold damage
noted was to the ceanothus, as the result of freezes during the winter of 2002
and 2003, when temperatures dropped abruptly into the low 20s. Significant
winter damage to the cistus or halimium has not been observed during the
evaluation. The results of these trials—I think—would apply to most gardens
west of the Cascades from southwestern British Columbia to northern California.
Ceanothus is probably known to most Northwest gardeners as
one of two fairly common evergreen shrubs. C. ‘Victoria’,
as it is commonly sold, is
an eight-by-eight-foot shrub with blue flowers in May and June. C.
Reyes creeper) is a low-growing plant with light blue flowers used as a
groundcover. Both of these are good plants that proved quite hardy. There is a
vast array of sizes and shapes between these two, however.
can be roughly divided into four groups: 1. Upright-growing shrubs such as ‘Ray
Hartman’ and ‘Blue Jeans’; 2. Large, rounded shrubs such as C.
thyrsiflorus var. thyrsiflorus ‘El Dorado’, ‘Dark Star’ or C. ‘Victoria’; 3. Mounding,
wide-spreading shrubs such as C. ‘Joan Mirov’, C. ‘Joyce Coulter’
thyrsiflorus var. griseus ‘Kurt Zadnik’; and 4. Low, spreading
groundcovers such as C. gloriosus, C. hearstiorum and C. ‘Centennial’.
Many of these are rarely grown in the Northwest, although they can be found in
specialty nurseries. Ceanothus can grow quite large—an important fact to keep
some of the plants were not very hardy. A freeze in early November 2002 did
serious damage to several cultivars, including most forms of C.
thyrsiflorus var. griseus. Some of these plants were, in fact,
killed. A striking exception to this was ‘Kurt Zadnik’, which suffered
relatively little damage. C. hearstiorum was also heavily
damaged, as was C.
thyrsiflorus var. thyrsiflorus ‘Snow Flurry’. Both of these partly
recovered. Others that suffered lesser damage, and recovered more or less fully
included ‘Centennial, ‘Joan Mirov’ and C. maritimus ‘Popcorn’.
Other plants in this
evaluation may have had some damage but recovered well. The plants that were
damaged can be grown in our region, but require a more protected site.
In looking for ceanothus of diverse size and habit for the
garden, quite a few performed well in this evaluation. Of the upright-growing
plants, ‘Ray Hartman’ was one of the best. It has a vase-shaped habit, and will
easily grow to 10 feet tall. It produces light blue flowers from early April to
mid-May. ‘Blue Jeans’ is an exceptional plant, forming a dense shrub to about
five feet tall and as wide. The small leaves give it an unusual texture, and
the light blue flowers are among the first of any ceanothus, appearing in early
March. Among the large, rounded shrubs, ‘Dark Star’ and ‘Julia Phelps’ are both
eight-by-eight-foot shrubs and are very striking with deep blue flowers from
late March through April. For a tall, drought-tolerant ground cover, there are
several good choices: ‘Wheeler Canyon’ grows to about six by ten feet, and
produces a profusion of blue flowers in late April. ‘Joyce Coulter’ is of
similar size and bloom time. ‘Joan Mirov’ grows to five feet tall and twelve
feet across and produces deep blue flowers through May. Finally, ‘Kurt Zadnik’
is a very large and striking groundcover, to six feet tall and fifteen feet
across and produces large clusters of deep blue flowers from late April through
If these are simply too large, there are smaller options. As
mentioned. C. gloriosus is readily available and low-growing. A really nice, dwarf
selection of this species, ‘Heart’s Desire’ grows to only a few inches tall and
four feet across. Both C. hearstiorum and ‘Centennial’—though a bit tender—are excellent
small-scale ground covers, and look great trailing over a wall. C.
also a bit tender, nevertheless forms a well-shaped bun only two feet tall and
four feet across. Finally, some of the hybrid ceanothus are very adaptable
plants. The best, and most showy of these was ‘Henri Desfosse’, which has
striking deep blue flowers, and apparently grows to about four feet tall and
wide. In our trial, it was grazed enthusiastically by deer, which reduced its
size dramatically. Most other ceanothus, by the way, seem pretty resistant to
Among the cistus and halimium, the most familiar and commonly
used by far are C.
and C. x purpureus,
both of which form dense, aromatic
shrubs (most cistus are distinctly and pleasantly aromatic) to four feet tall
and perhaps five feet wide. Both of these are good plants, although C. x purpureus
is a showier plant in bloom, but the
foliage quality of C.
is superior. Actually, in the
absence of any significant cold damage, it was plant form and foliage quality
that really separated good selections of these plants from poor ones. Some
cultivars which were very showy in bloom, such as ‘Victor Reiter‘, ‘Peggy
Sammons’ and ‘Silver Pink’, became very sparse and leggy as the trial went on,
and make poor specimens after only three years. The following suggestions are
all plants which retained excellent form and foliage throughout the evaluation
and flowered well.
Many of the Cistus have a mounded habit which makes them good
tall groundcovers for sunny sites with dry, poor soil—situations in which they
thrive. Several cultivars fit this description. ‘Snowfire’ grows to
four-by-six-feet and has white flowers with a red blotch at the base of each
petal from mid-May through June. C. x dansereaui
‘Decumbens’ is somewhat smaller, but
has similar flowers and flowers later. C. hirsutus and C. x laxus form
nicely-shaped domes about four
feet tall and six feet wide and have single, white, flowers.
Unlike the many dome-shaped or low-growing cistus, C. x aguilarii
is upright. It can reach seven feet
after four or five years, and will typically be about five feet across. It produces
large, pure white blooms in May. It is often sold as ‘Blanche’, though this is
not correct: ‘Blanche is a cultivar of C. ladanifer, a very
different plant. Some of the
halimiums also have an upright habit, and of these H. x pauanum is
probably the best for a
combination of bloom and foliage. It grows to six feet tall, features
grey-green foliage and has yellow flowers from late May through early July.
smaller garden, or even for large containers, there are several plants to
consider. The best known of these is C. x pulverulentus
‘Sunset’, which is widely available
and forms a mound of grey-green foliage two feet tall and four feet wide.
‘Sunset’ begins producing its brilliant magenta flowers in late May, and
virtually alone among the cistus, can have a few blooms as late as October.
‘Grayswood Pink’ is of similar habit to ‘Sunset’, although it seems to maintain
a tighter form and not open up the way ‘Sunset’ can do. ‘Grayswood Pink’, as
the name suggests, features pink flowers starting in early May.
of the x Halimiocistus, probably the best overall is x Halimiocistus sahucii, which forms
a dense mat barely one
foot tall and four feet across, with white flowers in May.
All of these plants not only flower well, they also maintain
an attractive appearance the rest of the year and seem tolerant of Northwest
weather. You might have to look around a bit before finding some of these
cultivars, but once found they will be great additions to the dry garden. NWGN