Ceanothus is a large genus of diverse, versatile and beautiful North American native shrubs in the buckthorn family Rhamnaceae, many native to California, and some endemic to Sonoma County. The genus includes over 60 species of shrubs or small trees. Most are shrubs from 1-6 feet high, prostrate or mounding, but C. arboreus and C. thyrsiflorus, both California natives, can be small trees up to 18-20 feet tall. Cal Flora Nursery in Fulton lists 31 varieties, of which only 4 are not California natives. Las Pilitas Nursery in Southern California delineates over 60. Common names of various Ceanothus species include California Lilac, mountain lilac, wild lilac, buckbrush, and, less commonly, blueblossom.
Ceanothus species are easily identified by their unique leaf-vein structure shared by all plants within this genus. The ovate leaves, mostly with serrated edges, have three prominent parallel veins extending from the leaf base to the outer margins of the leaf tips. The leaves normally have a glossy upper surface, and vary in size from 1/2 inch to 3 inches. Many of the very drought-tolerant species have spiny, holly-like leaves.
Ceanothus flowers are largely blue in a wide variety of shades, but a few are white or pink. The flowers are tiny and produced in large, dense clusters that are intensely fragrant—some say overly so. Bloom period is generally March into May. Ceanothus species are used as food plants by the larvae of some butterfly and moth species, and also attract bees and other beneficial insects, so can be considered components of a habitat garden, or an Integrated Pest Management program.
Several members of the genus can form a symbiotic relationship with soil micro-organisms and fungi, forming root nodules which fix nitrogen. This is a reason why fertilizing is not normally recommended--adding fertilizer may just kill off the good micro-organisms and make room for the bad ones. Ceanothus plants are better left fending for themselves.
The name Ceanothus comes from the Greek name keanothos, spiny plant. Ceanothus is also Latin for "thistle." Early California indians used the fresh or dried flowers of some varieties for washing, lathered into a soap. Such lather has been said to be relieving for poison oak, eczema and rash.
Ceanothus, by David Fross and Dieter Wilken, a comprehensive reference on the plant (see this month’s book review) states “Ceanothus thyrisflorus, blueblossom, was the first California species to receive both botanical and horticultural recognition . . . . “ when it was collected by botanist Adelbert von Chamisso on the Russian ship Rurik’s expedition to California in 1816. He continues “The Royal Horticultural Society received seeds of Ceanothus thyrisflorus from Richard Brinsley Hinds from the 1837 expedition of HMS Sulphur, making it the first California species introduced into European gardens “
“The intriguing material reaching England from California early in the 19th century persuaded the RHS to send a young Scotsman, David Douglas to the West Coast in search of ‘any interesting plants or seeds’ he found.” Douglas’s collections on the west coast included several Ceanothus species, and the Douglas Fir, which he introduced into cultivation in Britain in 1827, and which is perhaps the most famous plant named after him of the total of 240 species of plants which he brought back to England.
Even today, it is not uncommon in Britain to see Ceanothus espaliered against a south-facing brick wall.
Fross states “Ceanothus is best suited to gardens where conditions match or approach those where the plants are found in the wild. In many of the native California habitats of Ceanothus, there are a number of ecological similarities . . . soils drain well, and summers are dry. Ceanothus grows in a range of soil types but often is found on steep slopes in soils with low or marginal fertility. . . . . it is not surprising that most California species will endure long periods of drought, are intolerant of summer wet environment (or watering ) and require little or no fertilization.”
Good drainage seems to be a key with Ceanothus, as with so many native plants. If soil and drainage are less than ideal, plant Ceanothus rootballs a little higher than the surrounding grade. Or try to plant on slopes so the surface runoff drains more rapidly.
Most species need full sun, though in hotter areas (Sonoma Valley, Healdsburg) some afternoon shade is beneficial. In the garden, those tolerating summer irrigation are easily satisfied by one or two deep waterings a month when established. In more naturalized areas, or transition zones, no additional summer water should be applied after the second year after planting and later.
While most Ceanothus can be shaped by tip pruning (performed gratis by deer in the wild) and cleaning out interior or low dead growth, it resents serious hacking. Ceanothus will not produce shoots from old wood, so never prune back severely to old wood. Prune from the inside, lightly thinning, and removing a few lower limbs.
The ideal time to plant Ceanothus is late fall through early winter. This allows winter rains to foster adequate deep root growth needed to sustain it in the summer. Watering the following summer should be infrequent, yet deep, allowing the soil to dry out between soakings. Again, once established, Ceanothus needs very little or no water.
Ceanothus is often said to be short lived, but that may be mostly in garden that insist on drip irrigation, summer water and soil amendments. California native plants are generally intolerant of all of these. In their wild conditions Ceanothus plants have a natural life cycle of 10-15 years, with some even longer, though fire sometimes shortens that span.
Generally, the smaller and more prickly or leathery the leaf, the greater the deer resistance. The holly-leafed varieties, such as ‘Blue Jeans’ & ‘Mills Glory’, are thought by some to be more deer-proof than others. C. gloriousus seems also to be fairly deer resistant. Las Pilitas Nursery says “Some species are still viewed as candy in areas where deer populations are high. But many are OK in low or medium deer areas. If you have high deer problems stick with your local Ceanothus species and whatever you do, don't water!”
Phil Van Soelen, co-owner of Cal Flora native nursery in north Santa Rosa states that in his experience, the deer will still nibble these varieties, but only down to a certain level, and they then survive in a sort of hedged state. Dave Fazio, owner of Sonoma Mission Gardens in Sonoma states pretty emphatically that none are deer resistant in the face of hungry deer, save possibly the prostrate, small-leafed Ceanothus thyrsiflorus 'repens'.
Landscape and Garden Use
Versatile and useful many ways, Ceanothuses can be planted as specimens, screens, hedges, groundcovers, next to a wall, and in shrub borders. A great location is in transition zones, between more intensely cultivated and watered close-in gardens and the wild landscape. I recently planted ‘Blue jeans’ and ‘Julia Phelps’ in such an area in an oak woodland, along with companions toyon, coffeeberry, manzanita, sugarbush and deergrass. Time will tell how the Ceanothuses fare with the soil and drainage (moderate clay, and not so good), partial afternoon shade and deer freeway there.
Selected Species and Cultivars
A few Ceanothus species tolerate woodland or semi-shaded conditions: matlike C. prostratus and C. integerrimus (deerbush), for example. Species native to coastal areas and their cultivars—C. gloriosus (Point Reyes ceanothus) and C. griseus horizontalis (Carmel Creeper)—will accept and may require a limited amount of both shade and irrigation, but they must be given fast-draining soil.
Ceanothus ‘Ray Hartman’ behaves like a small tree, reaching 15 ft. tall and 10-15 ft. across. Its large clusters of medium blue flowers are quite showy in a landscape setting.
Among the medium sized varieties, ‘Dark Star' reaches about 6 feet and spreads out to 8-10, with reported good deer resistance. Tiny, crinkled, almost black-green leaves show off deep blue blooms. Infrequent summer irrigation is tolerated.
Ceanothus thyrsiflorus ‘Skylark Blue’ has dark green shiny leaves and medium blue flowers. It grows from 3 to 6 ft tall. It will adapt to clay and can tolerate limited deer browsing.
Ceanothus ‘Concha' is a garden-worthy cultivar, accepting summer water more forgivingly than most, with dark green and glossy leaves, and deep cobalt blue flower clusters in late spring. Grows 5-7 ft. high and 6-10 ft. wide. Tolerates summer irrigation and clay soil more than other species.
Ceanothus ‘Joyce Coulter,' has a large mounding form with trailing branches, 4 by 8 feet, with medium green leaves. It is covered in spring with wildly fragrant medium blue three-inch flower spikes. This is a great bloomer, drought tolerant, and somewhat deer resistant in areas of less pressure. Tolerates clay, summer irrigation, and shearing better than other cultivars.
Ceanothus ‘Blue Jeans’ has small prickly holly-like leaves and purple-blue flowers. It is a rounded shrub with arching branches. It grows about 6 ft tall. Blue Jeans likes full sun. Deer don't like it much.
Ceanothus ‘Julia Phelps’ reaches six feet near the coast and eight feet inland, and produces very showy, dark indigo flowers. Dark green leaves are small and crinkly, with serrated edges. The whole plant appears purple in spring as flowers emerge.
Ceanothus gloriosus ‘Hearts Desire’ grows to a foot or so with a dense ground covering habit. It has tough spiny leaves and so is not much eaten by deer. Native to the coast, it can tolerate interior heat with a bit of afternoon shade. It tolerates clay.
Ceanothus gloriosus 'Point Reyes,' is a taller shrubby groundcover, 2 ft by 8 ft. with light blue flowers, reddish snaking branches, and small leathery, rounded leaves of dark green with toothed margins resembling tiny holly leaves. Also needs afternoon shade inland, and may require minimal water in the summer. It is somewhat deer resistant.
by Sonoma County Master Gardener Steven Hightower