How to grow ceanothus (California lilac)
Find out all you need to know about growing ceanothus (California lilac), in this practical Grow Guide.
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It's unusual to find a shrub or tree with blue flowers, so if you're looking for a shock of blue to light up your garden, look no further than a ceanothus. When in flower it's a stunning sight, smothered in flowers in shades that range from powder blue to deep azure.
Most ceanothus flower for around six weeks from late spring to early summer, although some bloom from July or August, and some varieties bear white or pink flowers. Ceanothus come in a range of sizes. When not in flower, their small, dark green leaves can act as an attractive foil for other plants. The flowers are attractive to pollinators.
Also known as California lilac or Californian lilac, ceanothus are native to the Pacific coast of North America – California in particular. They are easy to grow, as long as you give the conditions that they enjoy in their native habitat – a sunny, sheltered spot, and well-drained soil. Most are evergreen; if your garden is exposed or in a cold area, choose a deciduous type that will be less susceptible to wind and frost damage in winter.
Ceanothus are fast-growing, long-flowering shrubs and as a result, can be shortlived – after around 10-15 years they may start to lose their shape and get rather leggy. As they don't respond well to hard pruning, it's best to replace plants at this stage.
California lilac: jump links
- Planting California lilac
- Caring for California lilac
- Propagating California lilac
- Growing California lilac: problem-solving
- Buying California lilac
- Best California lilac to grow
How to grow ceanothus
Grow ceanothus in moist but well-drained soil in full sun in a sheltered spot. Prune lightly in spring to maintain the plant's shape.
More on growing ceanothus:
Where to plant California lilac
Choose a spot in full sun, and moist but well-drained soil – avoid chalky soils, as the leaves have a tendency to turn yellow. In more exposed gardens, ceanothus will benefit from being planted near a south- or west-facing wall that will give some shelter from cold winds and winter frost. If you can’t provide shelter, choose one of the hardier, deciduous varieties.
Larger varieties can be grown at the back of the border, trained against a sunny wall, or grown as a free-standing shrub or small tree. Medium-sized varieties can be grown in the middle of a border or as an informal hedge. Mound-forming or prostrate forms can be grown as ground cover. They are a good choice for a cottage garden, wildlife garden, Mediterranean or gravel garden.
How to plant Californian lilac
Most ceanothus are best planted in spring. 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. If you are planning to grow your ceanothus against a wall, add some trellis beforehand. Water in well and continue to water in warm weather while it establishes.
Where to buy ceanothus online
Caring for ceanothus
Watering
Once established, ceanothus are fairly drought tolerant and should get most of the moisture they need from rainfall, except in very hot summers.
Deadheading
As ceanothus are usually smothered in flowers, it would be impractical to deadhead them. However you can remove spent blooms on plants if you wish, to keep them looking neat.
Pruning
Ceanothus do not need heavy pruning. If you have inherited an evergreen ceanothus that has outgrown its position or become slightly unshapely, it's not advisable to prune it back hard – it won't recover and is best replaced by a new plant. Deciduous ceanothus can be pruned back harder but will take a while to recover.
Evergreen ceanothus – prune spring-flowering varieties lightly after flowering, if needed – cut out dead wood and trim side-shoots. Prune later-flowering varieties in spring, cutting last year's woody growth back by around one third.
Deciduous ceanothus – prune deciduous ceanothus in early or mid spring, before flowering – cut back last year's woody growth.
Feeding
Ceanothus don't generally need feeding. However you could feed them after pruning to promote good new growth – feed with a balanced fertiliser or mulch around the base with well-rotted manure or garden compost.
Propagating ceanothus
For evergreen ceanothus, take semi-ripe cuttings from the current season’s growth, after flowering, any time up until the autumn. For deciduous varieties, take softwood cuttings from new growth in spring.
Pests and diseases
Ceanothus is a relatively pest- and disease-free shrub and should thrive, provided the planting conditions are right.
Yellow leaves may be a sign of nutrient deficiency, especially on thin or chalky soils.
Scorched or brown leaves and poor growth may be a sign that the plant is in too cold or exposed a spot.
Poor growth or dieback may be a sign that the soil that is too wet.
Ceanothus can be prone to scale insects and there is a chance it may succumb to honey fungus.
Advice on buying California lilac
- 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). 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 is 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 'Blue Cushion'
Ceanothus 'Blue Cushion' is a compact, evergreen shrub bearing small, oblong, dark green leaves. In late spring, fluffy dark-blue flowers are produced from reddish purple buds.
H x S: 1m x 2m
Ceanothus 'Cynthia Postan'
Ceanothus ‘Cynthia Postan’ is a beautiful Californian lilac, bearing masses of rich blue flowers in early summer. Hardy and evergreen, it's perfect for growing in a mixed or shrub border.
H x S: 3m x 2.5m
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 10C.
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.
Help! My ceanothus leaves have turned brown and crispy
This is probably due to frost damage. Depending on when the frost hits the plant, it could take out the young leaves or flowers. But if some leaves and flowers are held tight in bud then the frost will only affect the older leaves, and newer leaves and flowers will remain unaffected.
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