Californian at home in a warmer North.

Ceanothus originates from North and Central America with most of the 55 species being found in the south western United States - explaining the shrub's nickname California lilac. The flower heads may be reminiscent of lilac, but in fact ceanothus are members of the buckthorn family.

They were named ceanothus after the Greek kyanothos , meaning a spiny plant, though the connection is difficult to detect since the popular garden varieties are not thorny. The frothy flowers of most kinds are a true blue, unusual in flowering shrubs, ranging from pale hues to rich, deep shades. Most bloom in spring but a few types flower in summer or early autumn. Some are evergreen.

Ceanothus need sun, good drainage and a sheltered position, growing well against a south or west facing wall. They prefer to be planted in spring and dislike root disturbance, so the younger a shrub is when planted, the better it will grow.

Most varieties are susceptible to a few degrees of frost, but they are increasingly flourishing through winter in the North, presumably as a result of global warming. Some are fully hardy, such as the species Ceanothus thyrsifolius, which grows to 6m (20ft), "Topaze", with dark blue flowers on 1.5m (5ft) stems, and "Autumnal Blue," 3m (10ft) tall with sky-blue flowers in late summer and autumn.

Most like seaside gardens but they can be seared by really cold winds. They also object to soil which is too limey, though if the leaves show symptoms of chlorosis - yellow veins caused by high lime content - Sequestrene watered around the shrub regularly can help.

The evergreen kinds are best left unpruned, except after flowering to retain their shape. Deciduous types may be trimmed in March but should not be hard-pruned into growth that is more than a year old. There are varieties to suit walls of any height and some with a low, spreading habit. In gardens which are too exposed to keep ceanothus outdoors all year, dwarf forms can be grown in pots.

The most attractive and reliable evergreen kinds include:

* "Burkwoodii," a bushy shrub, 1.5m tall and 1.8m wide (5ft x 6ft) which bears bright, mid-blue flowers from late summer to autumn.

* "Cascade", which grows to 3.6m (12ft) and bears masses of powder-blue flowers in May and June on long arching branches which are easily trained against a wall.

* "Concha", a dense shrub with arching branches reaching 3m (10ft), on which dark red flower buds open to reveal deep blue blossoms in May.

* "Delight," growing 3m tall and 5m wide (10ft x 15ft), with deep blossoms in April and May, though too bushy to be trained easily against a wall.

* "Puget Blue" has sage green foliage and deep azure flowers from April to June on a shrub more than 2m tall x 1.2m wide (7ft x 4ft).

* "Cynthia Postan" is ideal for a small wall space, growing to 2m x 1.2m (6ft x 4ft) and with spreading, arching branches bearing small dark leaves and intense blue flowers in late spring.

There are a few white-flowered varieties, including Millerton Point, which produces honey-scented blossoms in spring on upright growth to 3m x 2m (10ft x 6ft), and Snow Flurries, also fragrant and of similar size but which blooms into July.

Ceanothus are not normally troubled by pests and diseases, except the killer honey fungus.

* There are three national collections in the Midlands and South, including one, containing 56 types, in the garden of a London square near Victoria Station. It is open by appointment through Mr R Phillips (0207 834-8654).