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How to grow ceanothus

How to grow ceanothus (California lilac)

Find out all you need to know about growing ceanothus (California lilac), in this practical Grow Guide.

A table displaying which months are best to sow, plant and harvest.
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Plant
Plant

Do not Plant in January

Do not Plant in February

Do not Plant in March

Do not Plant in April

Do not Plant in May

Do not Plant in June

Do not Plant in July

Do not Plant in August

Do Plant in September

Do Plant in October

Do not Plant in November

Do not Plant in December

Flowers
Flowers

Plant does not flower in January

Plant does not flower in February

Plant does not flower in March

Plant does not flower in April

Plant does flower in May

Plant does flower in June

Plant does not flower in July

Plant does not flower in August

Plant does not flower in September

Plant does not flower in October

Plant does not flower in November

Plant does not flower in December

Cut back
Cut back

Do not Cut back in January

Do not Cut back in February

Do not Cut back in March

Do not Cut back in April

Do not Cut back in May

Do not Cut back in June

Do Cut back in July

Do Cut back in August

Do not Cut back in September

Do not Cut back in October

Do not Cut back in November

Do not Cut back in December

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.

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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

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

Ceanothus ‘Concha’

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

Ceanothus thyrsiflorus var repens

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.


Growing ceanothus: problem solving

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 ‘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

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