Santa Clara County’s Ceanothus

Santa Clara County is home to about 11 species from the genus Ceanothus, commonly referred to as California lilac.  As with many ceanothus, our local species are found in dry, mountainous settings usually in ample sun.  Their glossy evergreen foliage is covered with white or blue flowers in spring.  While many ceanothus are available in the nursery trade, these are usually selections of coastal species or hybrids involving these species.  Local ceanothus are seldom available and rarely planted.

Hopefully this can change.  Landscaping with a plant that is locally native supports local ecology in unique ways.  Instead of a typical wilderness/urban interface that is characterized by contrast – summer dry versus summer moist, chemical-free versus chemical-dense, diverse local flora versus homogeneous non-native flora, etc. – we encourage an interface that is characterized by continuity.  Wildlife can enter the urban landscape and find supportive flora that mimics a wild setting.  For example, in Santa Clara County monarchs lay their eggs on narrow leaf milkweed, Asclepias fascicularis.   This milkweed is common in the wild, but almost never encountered in urban plantings.  Monarchs must return to a wilderness setting to lay their eggs.  By planting patches of narrow leaf milkweed, we support the monarch’s lifecycle in our neighborhoods.

Our local ceanothus provide similar benefits to local wildlife.  One example: Buck brush, Ceanothus cuneatus, supports the pale tiger swallowtail, Papilio eurymedon, and hedgerow hairstreak, Satyrium saepium, among many other butterfly species.  The abundant seed feeds local birds such as bushtits, Psaltriparus minimus, and goldfinches, Spinus psaltria, and many insects.  While there are non-native shrubs that provide some wildlife support, a locally native ceanothus supports numerous species in a variety of ways.  It has, after all, evolved with the local fauna.

Below I describe a few ceanothus to consider for your garden.  These are the most common ceanothus species in Santa Clara County.  If you are up for a hike, they all may be observed in the El Sereno Preserve above Los Gatos.

Buck brush, Ceanothus cuneatus:  This ceanothus is found in mountains and foothills throughout much of California.  It generally grows in an open, spreading form with dark leathery leaves.  It prefers a sunny location with well-draining soil.  It is one of the most fragrant ceanothus in bloom.  I once came across a large stand of blooming buck brush at Mount Madonna County Park.  The perfume from the snowy white flowers was a real pleasure.  This ceanothus once was common in the lower foothills of Santa Clara County.  For instance, one could find it in the rolling hills of Saratoga before they were developed.  Buck brush is the most likely species to have been present in the valley before development.

Jim bush, Ceanothus oliganthus:  Jim bush is endemic to California’s coastal and interior-coastal mountains.  On the inland side of the Santa Cruz Mountains it begins to appear at higher elevations than Buck brush.  It grows in a dense, rounded form with shiny leaves.  In late spring it is covered with small blue flowers.  Jim bush is among the largest local ceanothus, reaching a height of 10 feet or so.  It may be considered as a locally native replacement for larger ceanothus hybrids such as ‘Ray Hartman’ or ‘Frosty Blue.’  This species often grows alongside blue blossom, Ceanothus thyrsiflorus, and wartleaf ceanothus, Ceanothus papillosus and will hybridize with them readily.  In the El Sereno Reserve Jim bush predominates on the northern facing slopes, while Ceanothus papillosus is more common on the southeastern facing slopes.  Between them one finds hybrids displaying interesting combinations of the two species.

Wartleaf ceanothus, Ceanothus papillosus:  Wartleaf ceanothus is found in coastal and interior coastal mountains from the San Francisco Bay Area to Orange County.  It is named for the bumpy surface of its shiny, elongated leaves.  The form is open and rounded.  While the species may grow to eight feet or so, I have never encountered a specimen in the western mountains of Santa Clara County that exceeded four feet.  Wartleaf ceanothus requires well-draining soil and a sunny site.  Its dark blue flowers and shiny leaves recommend it for the landscape, but it is rarely available.  This is likely due to difficulties in cultivation – sun, heat and water must be offered in the right amounts at all stages or potted plants will abruptly “crash.”  It is thought to be one of the parent plants for popular hybrids such a Ceanothus ‘dark star,’ ‘Julia Phelps,’ and ‘Wheeler Canyon.’