Attractive blue, white or pink flowers make Ceanothus (or Californian lilac) a desirable shrub for a sunny, sheltered position.
Plant Ceanothus in fertile, well-drained soil in full sun. Avoid frost pockets and exposed situations. To provide shelter from strong, cold winds, Ceanothus is often best planted against a south-facing wall. Deciduous species and cultivars, such as ‘Glorie de Versailles’, can tolerate more exposed situations.
Mulch in late winter or spring with bulky organic matter, such as garden compost or well-rotted manure. Keep the base of the shrub free from mulch. To encourage new growth, apply general a balanced fertiliser after pruning in spring at 70g per square metre (2oz per square yard).
Pruning and training
Ceanothus shrubs are evergreen or deciduous, so prune according to what type you have.
Routine pruning is not essential and in fact are best not pruned. If grown as a bush, promote branching by pinch-pruning the soft tips on young plants in spring. Use secateurs to shorten over-long branches by up to a half in midsummer after flowering. Do not cut into older wood as the stumps may not regrow.
Late summer-flowering shrubs: These bear spring flowers on shoots that grew the previous summer and summer flowers on the current year's growth. Trim the previous season’s growth by one-third to a half in spring. (e.g. C. ‘Autumnal Blue’, C. ‘Burkwoodii’)
Late-spring and early-summer flowering shrubs: Prune after flowering. Cut back long, flowered shoots by one-third to a half. If more bushy growth is desired, trim lightly again in late summer. (e.g. C. arboreus ‘Trewithen Blue’, C. dentatus, C. impressus, C. thyrsiflorus ‘Skylark’)
To grow as a wall shrub see our advice in climbers and wall shrubs.
Prune deciduous Ceanothus (e.g. C. × delileanus ‘Henri Desfossé’ and ‘Gloire de Versailles’, C. × pallidus ‘Perle Rose’) in early to mid-spring. These bear summer flowers on new shoots each year and routine pruning is usually carried out to generate many strong new shoots each year.
First and second years: To develop the main framework of branches of free standing shrubs, shorten all stems by up to two-thirds, cutting back to an outward-facing bud. In the second year, prune the previous season’s growth by up to two-thirds and shorten all side branches to 10-25cm (4-10in) from the main stems.
On established plants: Prune main, flowered stems by about a half. Cut back weaker sideshoots harder – by up to about two buds. Thin out congested or unproductive growth from the centre of the shrub. The response of deciduous Ceanothus to hard pruning is usually good.
Renovating overgrown plants
Overgrown evergreen Ceanothus will not respond well to renovation pruning. In this case you'd be best off replacing the plant.
Propagating Ceanothus from cuttings is moderately difficult. From evergreens, take semi-ripe cuttings from mid-summer to autumn. Propagate deciduous shrubs from softwood cuttings from late spring to mid-summer.
Though Ceanothus can be grown from seed, it is difficult to germinate the seed and the plants will not come true to type. In late winter, pour hot water over the seeds and let to soak for 24 hours. Cold stratify for up to three months, and then keep at 16-18°C (61-65°F). Germination can take up to three months.
C. × delileanus ‘Gloire de Versailles’ AGM: A bushy deciduous shrub, bearing pale-blue flowers from midsummer to autumn. Height and spread 1.5m (5ft).
C. ‘Blue Mound’ AGM: A mound forming evergreen shrub, producing dark-blue flowers in late spring. Height 1.5m (5ft), spread 2m (6ft).
C. ‘Autumnal Blue’ AGM: An upright evergreen shrub bearing sky-blue flowers in late summer to autumn. Height and spread 3m (10ft).
C. thyrsiflorus ‘Skylark’ AGM: A bushy evergreen shrub producing dark-blue flowers in late spring to early summer. Height 2m (6ft), spread 1.5 (5ft).
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Do not plant in exposed situations and frost pockets as the plants can be affected by winds and frost injury. Prune back any frost damaged stems to healthy wood and remove dead stems in spring.
The root system can be damaged by excess moisture levels, leading to poor growth and dieback. Avoid planting in wet soils.
Ceanothus is lime tolerant, but plants can suffer from yellowing of the leaves between the veins (chlorosis) on shallow, chalky soils due to nutrient deficiency or cold soil conditions in spring.
It is also susceptible to honey fungus and scale insect attack.