I know spring has arrived when I begin to see ceanothus blooming in gardens around my neighborhood. It seems that many others appreciate ceanothus, as it is one of the most popular native plants in landscaping. Even after it finishes blooming, it is a pleasing light to dark green evergreen shrub that can fill a variety of design roles in the garden.
The many species in the Ceanothus genus vary widely, with growth habits that range from groundcovers to trees and flower clusters in colors that range from white to pale blue to violet to intensely dark blue. According to California Native Plants for the Garden by Carol Bornstein, David Fross, and Bart O’Brien, there are approximately 60 species and varieties of Ceanothus in the state: “The large number of ceanothus selections found in California gardens emanates from the extraordinary diversity this genus exhibits in the wild.” The book devotes several pages to the different growth habits of ceanothus, from large shrubs to medium-sized shrubs to ground covers. I highly recommend reading all the suggestions for which ceanothus to plant to fit your garden needs.
Ceanothus, also known as California lilac for its resemblance to showy European and Asian lilacs, is an important genus for wildlife. Insects, including butterflies, moths, and particularly native bees and honey bees, cover the flowers when they bloom in early spring in the Bay Area. In the summer and fall, the small dried flower pods hold seeds that are an important food source for birds and small mammals. Larvae of several species of butterflies and moths eat ceanothus leaves, and they in turn become food for birds. The birds find cover and nesting sites in shrubby ceanothus species.
I spent a weekend in early April driving around Berkeley, El Cerrito, Kensington, and Richmond to see how many different types of ceanothus I could find in gardens. It was truly amazing how many ceanothus plants I found! This genus is quite popular in local gardens, and the plants were all magnificently in bloom. I found one plant that was flowing down a short retaining wall; another was a small tree with deep blue blossoms. All were covered with bees—the sound of their buzzing was unmistakable.
Looking at Calscape, CNPS’s horticultural website, and entering my zip code to find natives that are well suited to my area, I find that blueblossom (Ceanothus thyrsiflorus) is one of the primary species recommended for my garden. Blueblossom is native to cooler parts of the Bay Area, with a few forays to warmer inland locales. It is generally widespread in coastal California, growing along almost the entire coast from Crescent City to San Diego. Calscape indicates that this species takes many forms in the wild, from two or three feet tall to tree height.
Blueblossom grows in full sun or part shade. Calscape recommends full sun in coastal areas, while in the inland parts of its range it will do better with more shade or on northern slopes. If you want to maintain a smaller, more compact plant, blueblossom responds favorably to tip pruning after it blooms. As a general rule, it’s best to prune ceanothus during the dry season to avoid infection, and to limit pruning to branches under one-quarter inch in diameter.
Blueblossom may tolerate clay or sandy soil, but like most ceanothus species it does best with good drainage. Ceanothus has a reputation for being short lived, but that is usually due to poorly drained soil and overwatering after the plant is established. To maximize the lifespan of ceanothus in your garden, Calscape recommends planting a species that’s native to your area and stopping direct watering after the first one to two years. Bornstein, Fross, and O’Brien note that in the wild, ceanothus tends to live 15-20 years.
I learned about an interesting aspect of ceanothus when I started doing some research: its roots contain nitrogen-fixing bacteria, which presumably help it grow in nutrient-poor soils. For this reason, it is not necessary, and often harmful, to fertilize ceanothus in gardens.
I highly recommend planting a ceanothus in your yard; among the many forms, species, varieties, and cultivars, I’m sure you can find one that is suited to your garden conditions!
— Robin Mitchell, Recording Secretary, CNPS East Bay Chapter
Note: California Native Plants for the Garden, by Carol Bornstein, David Fross, and Bart O’Brien (Cachuma Press, 2005), is difficult to find because it is out of print, but the Theodore Payne Foundation currently has it in stock.