In late spring a ceanothus in full bloom turns into a cloud of blue so intense it hums with bees. These Californian shrubs grow quickly, love a dry, sunny spot and ask for very little once settled, which makes them a favourite for walls and fences in UK gardens.
They do have a few quirks. Pruning at the wrong time, or cutting into old wood, can ruin a plant, and even a healthy ceanothus rarely lives as long as most shrubs. Here you will find what you need to know about siting, planting, pruning, wall training and getting the best years from your plant.
Ceanothus (California lilac) at a glance
- Botanical name Ceanothus, including evergreen forms such as 'Concha', 'Puget Blue' and C. thyrsiflorus var. repens
- Common name California lilac
- Plant type Evergreen or semi-evergreen flowering shrub, some grown as wall shrubs or ground cover
- Hardiness Mostly RHS H4 (down to about -10°C), with a few less hardy kinds
- Height and spread From 1m tall ground-covering forms to bushes of 3 to 4m or more, depending on variety
- Flowering Dense clusters of tiny blue flowers, mainly April to June, with some varieties flowering late summer to autumn
- Foliage Small, glossy dark green leaves, held all year on evergreen types
- Position Full sun, sheltered from cold drying winds, ideal against a warm wall
- Soil Light, well-drained soil, dislikes waterlogging and very shallow chalk
- Good for Wall training, bees, sunny banks, dry gardens
Sun, shelter and a warm wall
Ceanothus come from the dry hillsides of California, so they want as much sun as you can give them. Most evergreen varieties are rated RHS H4, hardy to roughly -10°C, but cold, drying winter winds can brown the small leaves and kill shoot tips.
A south or west-facing wall or fence is the ideal home in colder districts. The brickwork reflects heat, keeps roots drier in winter and protects the plant from the worst of the wind. In mild and coastal gardens, freestanding shrubs do well in an open sunny border.
Soil and planting
Light, free-draining soil suits ceanothus best. They grow happily in sandy and stony ground and tolerate some chalk, but on very shallow chalk the leaves can turn yellow from lack of iron. Heavy clay that stays wet in winter is the biggest threat.
Plant in spring, once the worst frosts have passed, so the roots have a full season to establish. Container-grown plants dislike root disturbance, so tease out circling roots gently and avoid breaking up the rootball. Water well and add a gravel or bark mulch to keep weeds down.
Watering and feeding, keep it lean
Keep new plants watered through their first summer, especially those planted at the foot of a wall where rain rarely reaches. After that, ceanothus are notably drought-tolerant and prefer to be on the dry side.
Do not overfeed. Rich soil and high-nitrogen fertiliser produce lush, soft growth that flops, flowers less and suffers more in frost. A light dressing of general fertiliser in spring is plenty on poor soils, and many plants need nothing at all.
When to prune evergreen ceanothus
Timing depends on when your variety flowers, and the golden rule is never to cut back into old, bare wood. Ceanothus rarely sprout from leafless stems, so a hard cut often leaves a permanent gap or kills the branch.
- Spring-flowering evergreens, the majority, are pruned straight after flowering in early summer.
- Late summer and autumn-flowering evergreens, such as 'Autumnal Blue', are trimmed lightly in spring.
- Shorten the current season's shoots by up to half, always cutting within green, leafy growth.
- Deciduous types such as 'Gloire de Versailles' are different and can be cut back harder in early spring.
Training ceanothus on a wall or fence
Fix horizontal wires or a trellis about 30cm apart and a few centimetres away from the wall to allow air to move behind the plant. Plant around 45cm out from the base of the wall, where the soil is less dry, and lean the stems back towards the support.
As the shrub grows, tie the main stems in to form a fan, keeping them spaced evenly. After flowering each year, cut back shoots growing straight out from the wall to a couple of buds and tie in new stems to fill gaps. Started young, a wall-trained ceanothus stays flat and tidy for years.
A short but glorious life
Most ceanothus live for around 5 to 10 years, sometimes a little longer in a perfect spot. They grow fast, flower heavily and then become woody and sparse, and older plants can die suddenly after a hard winter or a very wet spell.
Rather than battle with a tired, leggy plant, enjoy it while it is at its peak and plan a replacement. Semi-ripe cuttings taken in mid to late summer root fairly easily in gritty compost under cover, giving you a young plant ready to step in.
Pests, problems and garden partners
Scale insects sometimes appear on stems, leaving sticky honeydew and black sooty mould. Yellowing leaves usually point to shallow chalk or waterlogging, and frost-browned foliage should be left until spring before trimming. Ceanothus are not generally considered harmful to people or pets.
The blue flowers look superb with yellow and white. Try rock roses, euphorbias and lavender at the base, or let a clematis scramble through a wall-trained plant. For more sun-loving companions, browse our drought-tolerant plants.
Questions about Ceanothus (California lilac)
Can I cut back an overgrown ceanothus?
Usually not successfully. Evergreen ceanothus seldom regrow from old, bare wood, so a hard prune often kills the branches or the whole plant. It is better to trim regularly from the start and replace a very overgrown shrub.
Why has my ceanothus died suddenly?
Sudden death is common in older plants, often after a cold, wet winter that damages the roots. Waterlogged soil, severe frost and simple old age are the usual culprits, as most plants only live 5 to 10 years.
How fast does ceanothus grow?
Ceanothus is one of the faster evergreen shrubs and can put on 30 to 60cm a year in good conditions. Many varieties flower well within two or three years of planting.
Is ceanothus evergreen?
Most ceanothus sold in the UK are evergreen and keep their small glossy leaves all year. A few, such as 'Gloire de Versailles', are deciduous and lose their leaves in autumn.
Give a ceanothus sun, sharp drainage and careful pruning, and it will repay you with spectacular blue flowers every spring. You can find it and other sun-loving evergreens in our shrubs collection.