Because they don’t tolerate hard pruning, make sure you plant the shrub somewhere they will have enough space when fully grown.
Light
A full sun location is best for California lilacs, but afternoon shade can be advantageous in the hotter southern regions. Too much shade, however, will result in disappointing blooms.
Soil
California lilacs do well in most soil types, providing they’re well-drained. They like fertile conditions that aren’t too heavy or soggy. Chalky soils can cause yellowing leaves. If drainage isn’t excellent, you can plant the shrub on a mound or slope to promote fast runoff. It’s also worth adding organic matter to amend the soil to promote better drainage.
Water
Newly-planted shrubs need regular, deep watering, but, once established, California lilacs are pretty drought-tolerant and cope well in arid conditions. When there are prolonged hot, dry spells, they may need additional irrigation to promote healthy growth and blooms. Otherwise, they won’t generally relish supplemental watering. It’s best to do a single deep soaking, though, rather than little and often. Wet soils are not appreciated, and you should allow the soil to dry between waterings. This means automatic irrigation systems can be problematic for this species.
Temperature and Humidity
Many ceanothus species are native to California, and they appreciate Mediterranean-style climates with mild, wet winters and hot, dry summers. The rarer, hardier deciduous species can handle wind and frost damage better than the evergreen varieties.
Fertilizer
These shrubs do well in infertile conditions and have natural nitrogen-fixing abilities, so they don’t generally need feeding. However, if you want to encourage vigorous new growth after pruning back, you can mulch around the base of the shrub with some garden compost, taking care not to mulch up the stem.
Types of California Lilacs
Ceanothus come in a wide variety of sizes and growing habits. Evergreen species are much more widely available, but selecting a hardier deciduous type makes sense if you have a more exposed garden. Some popular species cultivars include:
Ceanothus (Concha): One of the most popular, adaptable and hardiest evergreen ceanothus hybrids. It reaches five to 10 feet high, and flowers appear in the late spring. The branches cascade, so it’s best as a specimen rather than a wall-trained shrub. Ceanothus thyrsiflorus var. repens AGM: A very hardy evergreen that grows in a wide mound form. You’ll often see it cascading over low walls. Ceanothus thyrsiflorus (Skylark) : Can handle slower draining soils and colder temperatures more than many other ceanothus and has a long bloom period. Ceanothus × delileanus (Gloire de Versailles) AGM: A strong, deciduous shrub with large, glossy green foliage and loose soft-blue blooms that grow through summer and fall. Typically grows to 5 feet tall.
Pruning
These shrubs don’t need a lot of pruning. In fact, hard pruning of the evergreen species can be problematic, weakening their integrity and causing issues. Pruning just the tips of the branches after it has finished flowering can help to keep a compact shape. Lightly pruning out the foliage-free interior branches can also help to promote new growth and keep air circulation flowing well. Do this right after the bloom season is over. Deciduous ceanothus can cope with harder pruning, cutting back the last years woody growth in the early spring.
Propagating California Lilacs
Ceanothus are relatively easy to propagate from cuttings and usually produce a flowering plant within two to three years. It’s best to take semi-ripe, current season’s growth cuttings from evergreen varieties after flowering in summer or autumn. For deciduous species, take softwood cuttings from new growth on non-flowering stem tips in the spring. Dip the cutting in rooting hormone and keep it in a warm, humid spot (for evergreen varieties keeping them in a propagator can help). Evergreen ceanothus typically require a growing season to root well before planting out. Deciduous types should take around four to six weeks to take root.
How to Grow California Lilacs From Seed
Growing ceanothus from seed is possible, but it can be tricky, and named cultivars won’t come true to type when produced by this method. They have a hard seed coat and because of their dormancy, they need to soak in hot water for at least 24 hours. You’ll then need to stratify them for around three months. When you sow them, they need to be kept in a warm environment of about 60 to 65 degrees Fahrenheit. It can take up to three months for the seeds to germinate.
Common Pests & Plant Diseases
One of the attractive qualities of ceanothus species is that they aren’t troubled by too many serious pests or diseases. However, they can be bothered by scale insects, and honey fungus disease is occasionally a problem.
How to Get California Lilacs to Bloom
The abundant blooms of California lilacs are what attracts most gardeners—and pollinators, like bees—to these species. The tiny flowers form in large clusters, and the shrubs can be in bloom for around six weeks (some cultivars have an even longer bloom period). Bloom times and lengths vary depending on the species and cultivar. Some flower from late spring to summer, others from summer to fall. Most come in shades of blue, but a few cultivars produce white or pink flowers. Ceanothus x pallidus (Perle Rose) AGM is one deciduous cultivar that has bright pink blooms. Some cultivars, like Ceanothus (Joyce Coulter), are also known for their fragrant blooms. Deadheading isn’t practical giving how many blooms ceanothus produce, but you can remove spent blooms to maintain a neat appearance and improve vigor. Too much shade and overwatering can reduce bloom success.
Common Problems with Ceanothus
Ceanothus is an easy plant to grow, but if it doesn’t get the conditions it needs, you can see problems. These include:
Saturated, poorly draining soils can cause root rot Chalky soils can lead to yellowing foliage because of a lack of appropriate nutrients Windburn and frost damage is possible if your shrub is planted in an overly exposed location
