How to grow ceanothus
All you need to know about growing ceanothus (California lilac), in this practical Grow Guide.
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Californian lilacs (Ceanothus) are woody, shrubby plants in sizes that range from ground-covering bushes up to a small tree. Native to the Pacific coast of North America, they make a spectacular sight when in flower, bearing masses of blooms in shades from pale blue to deep azure, plus there are white and pink varieties, too. Most ceanothus flower for around six weeks, from late spring to early summer, although some bloom later in summer. Ceanothus flowers are not only beautiful but are also attractive to pollinators, particularly bees.
Ceanothus are sun loving and drought tolerant. Most have evergreen foliage, though some are deciduous, which is useful in colder areas as deciduous plants are less susceptible to cold damage than evergreens. These handsome shrubs are fast-growing and establish quickly, although they tend not to be long lived.
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Where to grow ceanothus
Grow ceanothus in a sunny, sheltered spot, in well-drained soil. Avoid chalky soils, where leaves tend to turn yellow. In cold or exposed gardens, plant ceanothus in the shelter of a sunny south or west-facing wall, or choose one of the hardier, deciduous varieties.
Plant larger varieties such as Ceanothus ‘Concha’ at the back of the border, trained against a wall or fence, or grow as a free-standing shrub or small tree. Medium-sized varieties like Ceanothus ‘Skylark’ can be grown in the middle of a border or as an informal hedge. Mound-forming or prostrate forms such as Ceanothus repens can be grown as ground cover. When growing ceanothus against a wall or fence, choose a flower colour to contrast against its backdrop. For example, the most intense blue-flowered ceanothus, such as the varieties 'Puget's Blue', 'Concha' and Ceanothus impressus, look spectacular against a pale wall.
How to plant ceanothus
Plant ceanothus in spring to give a full growing season to establish before winter. Dig a generous hole that is slightly larger than the rootball. If you are gardening on heavy soil, dig in some organic matter, such as garden compost or well-rotted manure, to improve drainage. If you are planning to grow your ceanothus trained against a wall or fence, put up wires or trellis before you plant. Water in well. Ceanothus do not thrive in pots, due to their fast growth and spreading roots.
Where to buy ceanothus online
How to care for ceanothus
Keep watered during dry spells for the first growing season. Thereafter, ceanothus are drought tolerant and should get most of the moisture they need from rainfall, except in very hot summers. Most ceanothus have evergreen foliage and look good right through winter, covered with many small, crinkled, mid to dark green leaves.
Feeding ceanothus is rarely needed unless soil is very poor or if plants have been hard pruned. Instead, mulch around the base with well-rotted leaf mould or garden compost.
How to prune ceanothus
Lightly prune spring-blooming varieties immediately after flowering, or summer-blooming varieties in mid-spring. First, cut out dead wood and trim side-shoots, then cut last year's woody growth back by around one third.
Ceanothus do not respond well to hard pruning and are best not pruned unless they have outgrown their position. If your ceanothus has become leggy or misshapen, it is best to replace it with a new plant.
How to propagate ceanothus
Take semi-ripe cuttings from the current season’s growth of evergreen ceanothus, from summer to autumn. For deciduous varieties, take softwood cuttings from new growth in spring.
Pests and diseases
Ceanothus isn't susceptible to pests and diseases, providing the planting conditions are right.
Brown and crispy leaves may be a sign that the plant is in too cold or exposed a spot, and has suffered from frosty conditions. Wait until mid-spring before trimming off frost damaged leaves.
Yellow leaves may be a sign of nutrient deficiency, especially on thin or chalky soils.
Poor growth or dieback may be a sign that the soil that is too wet, or dry. If too dry, give it an occasional drink, though avoid watering when temperatures are below freezing.
Ceanothus can be prone to scale insects and there is a chance it may succumb to honey fungus.
Advice on buying ceanothus
- Ceanothus are widely available in garden centres but for the best choice of varieties, you may need to look online
- Taller varieties are often tied onto a support, which shows that they would be a good plant for training against a wall
- Look for a healthy shape and healthy, dark green leaves
- If your garden is cold or exposed, choose a deciduous variety
Where to buy ceanothus online
Ceanothus varieties to grow
Ceanothus 'Concha'
Vivid blue flowers appear on arching branches in late spring. This evergreen variety may need protection in very cold winters. The Royal Horticultural Society has given it the prestigious Award of Garden Merit (AGM). Ceanothus 'Concha' can be grown against a wall or as an informal hedge.
Height x Spread: 3m x 3m
Ceanothus thyrsiflorus var. repens
Ceanothus thyrsiflorus var. repens is one of the hardiest varieties, with pale blue flowers. It's a low-growing evergreen, forming a natural mounded shape and looks good at the front of a mixed border, or grown as ground cover. It holds the RHS AGM.
H x S: 1m x 2m
Ceanothus 'Autumnal Blue'
Ceanothus ‘Autumnal Blue’ is an unusual, late-flowering variety, blooming from August to October. It is evergreen, with an upright habit. It's hardy, but needs protection from strong winds. Another variety that holds the RHS Award of Garden Merit.
H x S: 3m x 3m
Ceanothus 'Puget Blue' – a popular variety of California Lilac with conical, deep blue flowers that smother the evergreen foliage. This hardy shrub is ideal for the back of a borders and can be trained against a sunny wall, or grown as a tall, informal hedge. RHS AGM.
H x S: 2.5m x 2.5m
Ceanothus 'Skylark' - a bushy evergreen that is smothered sky-blue flowers in late spring. It can be grown as an informal hedge or to add structure to a border. Protect from cold winds.
H x S: 1.5m x 2m
Ceanothus 'Gloire de Versailles' – a hardy, deciduous variety that is more suitable for colder gardens. It bears powder blue flowers in July and August that are attractive to pollinators.
H x S: 1.5m x 1.5m
Ceanothus 'Marie-rose' – an unusual variety with pink flowers in late summer that are followed by red seed capsules.
H x S: 2m x 2m
Frequently asked questions
Help! The leaves of my ceanothus are turning yellow!
Ceanothus can be drought-tolerant once established, but newly planted plants can suffer if planted into too-dry soil, while over-watering could lead to established plants developing yellow leaves. Push your fingers into the soil around the rootball. If it's dry then give your ceanothus a good drink – at least two watering cans' worth – and administer this slowly so it soaks into the soil. Repeat weekly until the plant shows signs of improvement. If the soil is wet then stop watering until it has dried out. If it doesn't dry out you will need to look at moving your ceanothus, as it won't thrive in waterlogged soil.
How do I transplant a small ceanothus?
Autumn is the best time to move a shrub, while the soil is still warm enough for root growth and will allow the plant to re-establish before the big spring push to make new leaves and flowers. Water the plant liberally an hour or two before you want to move it and let it soak. This will reduce root disturbance. Dig it out with as much root ball as possible and plant it again immediately in a well-prepared hole. Firm it gently and make sure it's at the same depth as it was before and then water thoroughly. If it's the evergreen form, water in dry spells after moving and until temps dip below 10ºC.
Which ceanothus has the most intense blue flowers?
The varieties 'Puget's Blue' and 'Concha' are said to have the most intense blue flowers of any ceanothus.
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