The Ceanothus is a genus from the buckthorn family (Rhamnaceae) and is commonly named California lilac, buckbrush, soap bush or just ceanothus.
The California lilac is native to North America and is a genus of more than 60 species. Most species come from the western coast of North America. Most California lilacs are 0.5 to 3 metre (20 inches to 10 feet) high shrubs, but there are also small trees and ground covering plants. The majority is evergreen, but some species that have adapted to cold winters are deciduous. The leaves are shiny. Many of the species that are very drought tolerant have spiny, holly-like leaves.
The word ceanothus comes from the Greek (keanothos) and means ‘spiny plant’.
A Ceanothus grows best if you neglect it. In the first year they need some extra watering but once established they hardly need anything. In dry periods they might need some watering once or twice per month, but in areas with adequate rainfall that is not necessary. They do not like moist or fertilization. You can add organic mulch around the roots zone, but nothing else. With a rich soil or too much fertilization and moist the plant grows too fast which makes it more vulnerable to fungal infections and frost.
The Ceanothus grows well in most soils as long as it is well-drained and not moist. It is tolerant to drought, heat and salt and also produces beautiful, fragrant flowers. They mostly prefer full sun, but some shade will be tolerated.
The flowers appear in terminal clusters of deep blue, but some California lilacs bear lighter blue, lavender or even pink or white flowers. Most Ceanothuses bloom in spring, but some species bloom in summer or autumn. The flowers attract bees and butterflies.
The way to prune a Ceanothus depends on the flowering time and whether the plant is evergreen or deciduous:
- The late spring and early-summer-flowering evergreens are best pruned immediately after flowering. Cut back long, flowered shoots by one-third to a half. Examples of this species are Ceanothus arboreus ‘Trewithen Blue’, C. dentatus, C. impressus and C. thrysiflorus ‘Skylark’.
- Evergreens that bloom in late-summer bear flowers on shoots that are produces in that year. You can cut back shoot from last year by one-third to a half in spring. Examples of this species are Ceanothus ‘Autumnal Blue’ and C. ‘Burkwoodii’.
- The deciduous species need some extra attention in order to flower well. The flowers grow on new growth and it is best to prune them in early- to mid-spring to encourage strong new shoots. Examples of this species are Ceanothus x delilianus ‘Henri Desfossé’ and C. x pallidus ‘Perle Rose’. In the first year try and develop a framework of branches by shortening all stems by two-thirds to an outward facing bud. In the second year, prune the previous season’s growth for about two-thirds and shorten the side-shoots to 10-25 cm (4-10 inches) from the main stems. From the third year on cut back the main, flowered stems by about half. Cut weaker stems back harder to about two buds from the main stems. Thin out the centre of the plant by cutting the congested and unproductive growth.
In Europe breeders crossed hardy, white-flowered, deciduous Ceanothuses (like C. americanus) with more tender, blue-flowered, evergreen Ceanothuses (like C. coeruleus) in order to create blue-flowered, hardy plants. The result is, amongst others, the Ceanothus x delilianus which is commonly called the French hybrid. The best known French hybrids are ‘Gloire de Versailles’ with powder blue flowers and ‘Henri Desfossé’ with deep blue flowers.
The Ceanothus x delilianus ‘Henri Desfossé’ blooms on new shoots of the same year. The stems of the new shoots are wine-red. In mild winters this California lilac is semi-evergreen. Because the roots go deep into the ground this plant can withstand droughty conditions, but this also makes it hard to transplant it once established.
The name is sometimes written differently: Henri Défossé, Henri Defosse, Henri Desfosses and Henri Desfosee. It is unclear what the correct spelling is. That also goes for the word delilianus. I also encounter the word delileanus often and it is unclear what the correct spelling is.
Attracts bees: yes
Exposure: sun/part shade
Flower colour: blue
Flowering time: June - July
Foliage colour: green
Fragrant flower: yes
Hardiness: -15 ºC (5 ºF)
Height: 5 feet (1.5 m)