A true blue is a rare commodity in the garden, especially in the first half of summer, but there’s one shrub that delivers and that’s ceanothus. Although commonly called Californian lilacs, because the showiest ones are raised from species found close to the Californian coast, their abundant flowers are an intense deep-blue and not a wishy washy lilac. Many have handsome, dark-green evergreen foliage and this, combined with weeks of tight, blue flowerheads, makes for an eye-catching combination from May onwards. The buds can be pretty spectacular too, they’re often tinged in red and purple.
Ceanothus were planted in early American gardens. However they only came to Britain, via France, in the mid 19th century when the famous Hackney nursery, Loddiges imported C. azureus from Empress Josephine's famous garden at Malmaison. There are now many named forms on offer, mostly evergreens.
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Evergreen ceanothus need a sheltered, sunny position in British gardens, away from biting easterly winds, because hard British winters can cut them back. In the wild they enjoy a Mediterranean-style climate of mild, moister winters and hotter, drier summers. Several species are found on the high chaparral, on scrubby free-draining slopes, so they prefer well-drained soil and a sunny position. They don’t need watering once established, or feeding, because they’ve evolved on poor soil.
Their ability to tolerate dry conditions and hot summer sunshine makes them excellent wall shrubs for a south- or west-facing position.
They can also be used as free-standing plants in garden hot spots. Ceanothus grow on a range of soils, including alkaline, but they can struggle on thin soil above chalk.
Ceanothus roots dig deep for moisture, so once planted evergreen ceanothus resent disturbance. They also resent being radically pruned, although the thinner newer growth can be clipped and tidied after flowering.
They flower gloriously, but tend to be short-lived, possibly lasting from seven to ten years or so. If a ceanothus begins to fade away, it will need replacing because these fast-growing shrubs simply run out of energy. Semi-ripe evergreen cuttings, taken in summer, root easily in a propagator that provides bottom heat.
Read our guide to choosing low-maintenance garden shrubs
Where to plant ceanothus
California lilacs are found naturally on sloping ground in the drier, sunnier parts of the United States. Gardeners must emulate these conditions by providing good drainage and a sheltered position. This may mean a south-facing wall or sun-baked shelter out of prevailing winds.
Ceanothus are happy in free-draining alkaline or acid soils away, less so on chalk and wet clay - although drainage can be improved by adding coarse grit to the ground.
Mound-forming varieties can be grown in windier, colder sites but still need good drainage.
California lilac (ceanothus) 'Skylark'
Wall-grown ceanothus should have their long growth trimmed back in August or September to prevent wind damage later in the year.
Shrubby evergreen ceanothus only need a light tidy after flowering. If winter frosts brown some of the leaves remove them in April.
Deciduous ceanothus need to have the old wood pruned back in spring and this will keep them vigorous.
Evergreen ceanothus tend to perform well for six or seven years and then lose vigour and die. Deciduous forms are longer lived.
Taking ceanothus cuttings
Take cuttings of semi-ripe wood from August until October, placing the 6in lengths of stem in a half-and-half mixture of soil-based gritty compost and horticultural sand. These should root over winter, but may take longer, for potting up individually in gritty compost and planting in late spring.
Award-winning evergreen ceanothus to grow
Ceanothus come in all shapes and sizes, because there are 55 species spread across North and Central America. Evergreens vary in habit from the lanky, tree-sized C. arboreus, commonly called the Catalina Mountain Lilac, to the mound-forming C. thyrsiflorus var. repens found in California and south Oregon. It’s important to choose the right ones.
This easily-grown hybrid is widely available and one of the hardiest of all. It’s best grown as a specimen shrub, because the branches arch over and cascade downwards. The intense blue flowers emerge from red-tinted buds framed by a backdrop of crisp, dark evergreen leaves. One of the best! 3m/ 10ft
C. arboreus ‘Trewithen Blue’ AGM
Slightly scented, mid-blue flowers held in six-inch long clusters appear in late-spring and early summer. The round oval foliage is distinctive and the conical flowers look almost fuzzy. It is often trained on a wall, but it’s best seen in free-flow, because it’s very graceful. It came from Trewithin House and Gardens in Cornwall, and it does needs space and a warm position. Up to 9m in warm climates/ 30ft
'Puget Blue' AGM
This spreading ceanothus is widely available, and it turns blue when it flowers because the foliage gets completely obscured by a mass of tiny flowerheads. It’s very fast-growing and this one is recommended for clay soil, although this good performer is very tolerant of all conditions. It’s one of the hardiest too. 2.0 x 2.0m/ 7 x 7ft
Named because the long clusters of clear-blue flowers tumble downwards. The slender, shiny green foliage is very neat, so it’s suited to being grown on a wall. 4m/ 13ft
‘Dark Star’ AGM
The name refers to the small dark leaves and burgundy-coloured buds, which look almost black from afar. The fragrant cobalt-blue flowers are also very vibrant. It can be grown as a hedge in warm positions, on well-drained soil. 2 x 2.5m/ 6ft x 8ft
Ceanothus thyrsiflorus ‘Skylark’ AGM
A dense, compact ceanothus with mid-blue flowers held above small toothed green leaves. 2 x 3m/ 6 x 10ft
Ceanothus thyrsiflorus var. repens AGM
This mound-forming evergreen is one of the hardiest of all, forming a low but wide mound of shiny foliage and mid-blue flowers from late spring onwards. It’s very effective tumbling over a low wall. Up to 1.5m x 2m / 5ft x 6ft
Ceanothus ‘Autumnal Blue’ AGM
This is later flowering, producing fluffy clusters of sky-blue flowers from August to October. This strong, upright ceanothus has bright-green glossy, small leaves. It’s ideal for a sunny wall, or at the back of a south or west-facing shrub border. It needs protection from strong winds. 3m/ 10ft
Ceanothus ‘Tuxedo’ PBR
This new California lilac is a sport, a shoot showing different characteristics, that came from Ceanothus ‘Autumnal Blue’. It’s the first one to have purple-bronze, evergreen foliage. It flowers prolifically in late summer and early autumn.
Deciduous ceanothus varieties
Deciduous varieties of ceanothus are hardier, but they still need a sheltered position that isn’t prone to spring frosts. They rely on being pruned in March or April for their survival. Last year’s new growth, which is paler in colour, should be cut back to the base of the previous year’s wood to allow the whole plant to reshoot vigorously again. A good mulch after pruning is a help. Give them a warm wall (or a warm position) and full sun. They are fairly hardy, to -10C (14F).
Ceanothus × delileanus 'Gloire de Versailles' AGM
This deciduous, medium-sized shrub has large green leaves and loose panicles of soft-blue flowers between July and October. It’s the strongest of its type. 1.5m/ 5ft
Ceanothus x pallidus ‘Perle Rose’ AGM
This similar deciduous ceanothus has bright-pink flowers. 1.5m/ 5ft
Good companions for California lilacs
The yellow daises of Anthemis tinctoria 'E C Buxton', tall dark bearded irises, Phlomis russeliana and apricot and yellow rock roses ('Chocolate Blotch' and 'Wisley Primrose'), will all thrive in front of ceanothus in a sunny border.
In my opinion, blue ceanothus against sun-baked walls are best grown as solitary specimens to make the most of their arching branches and sweetly fragrant flowers. However, you can use repeat-flowering climbing roses as partners if the roots are slightly shaded by the ceanothus. The silver-pink 'New Dawn', the pale-pink 'Blairii Number Two' or the apricot 'Gloire de Dijon' blend softly with blue.
Find out about other types of blue flowers for the garden, or read about how to use colour in your garden design
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