California lilacs (Ceanothus spp.) are evergreen and deciduous shrubs with clusters of tiny flowers that come in light to dark blue and sometimes white. The leaves are usually dark green and glossy and sometimes resemble holly leaves. A few varieties offer variegated leaves. California lilacs need full sun except in very hot areas, where a little afternoon shade is appreciated. They need good drainage and are drought tolerant. They grow well in U.S. Department of Agriculture plant hardiness zones 7 through 10. (source 6)
Light Blue Varieties
A number of Ceanothus cultivars bear pale powdery blue flowers, a color rarely found in nature. Some flower colors are blue but some colors lean toward purple. "Blue Jeans" (Ceanothus x "Blue Jeans) and "Point Reyes" (Ceanothus gloriosus "Point Reyes"), for example, bear lavender-blue flowers. "Point Sierra" (Ceanothus maritimus "Point Sierra") and "Gloire de Versailles" (Ceanothus x delilianus "Gloire de Versaillle") are somewhat lilac-blue. The species Ceanothus ramulosus bears pale, dusty blue flowers and the stems twist slightly.
Dark Blue Varieties
Dark blue flowers really stand out against dark green leaves, and create a bold landscape addition. As with the lighter-colored varieties of ceanothus, some colors are blue and others are more purple. "Julia Phelps" (Ceanothus "Julia Phelps") bears dark indigo blue flowers, while both "Concha" (Ceanothus "Concha") and "Italian Skies" (Ceanothus "Italian Skies") bear nearly true blue flowers with only slight purple shading. "Dark Star" (Ceanothus x "Dark Star") and the species Ceanothus hearstiorum both bear purple-blue flowers, while "Ray Hartman" (Ceanothus "Ray Hartman") has dark lilac-blue blooms.
Although Ceanothus varieties that bear white flowers aren't that common and the blue varieties tend to get all the attention, these plants can be quite pretty and deserve to be planted more often. Both of the cultivars "Snowball" (Ceanothus rigidus "Snowball") and "Snow Flurry" (Ceanothus thyrsiflorus "Snow Flurry") bear white flowers, but "Snow Flurry's" flowers are larger and more elongated. Two species, Ceanothus crassifolia and Ceanothus megacarpus, both bear white flowers and are native to California.
Ceanothus with pink flowers are fairly rare, however, at least a couple of pink-floering cultivars exist. "Marie Simon" (Ceanothus x pallidus "Marie Simon") bears feathery pink flowers, while "Perle Rose" (Ceanothus x pallidus "Perle Rose") has large, salmon-pink blooms. Leaves may be variegated with either yellow or white accents. "Diamond Heights" (Ceanothus griseus "Diamond Heights") and "El Dorado" (Ceanothus thyrsiflorus "El Dorado") have yellowish-green variegation, while "Silver Surprise" (Ceanothus griseus horizontalis "Silver Surprise") has white variegation. All the variegated varieties bear pale blue flowers.