Common Name: blue mountain lilac
Type: Broadleaf evergreen
Family: Rhamnaceae
Zone: 7 to 10
Height: 4.00 to 5.00 feet
Spread: 6.00 to 7.00 feet
Bloom Time: May to June
Bloom Description: Blue
Sun: Full sun to part shade
Water: Dry to medium
Maintenance: Low
Suggested Use: Hedge
Flower: Showy
Leaf: Evergreen
Attracts: Birds, Butterflies
Other: Winter Interest
Tolerate: Drought, Erosion, Clay Soil, Dry Soil, Shallow-Rocky Soil
Culture
Best grown in evenly moist to dry, well-draining soils in full sun to part shade. Best flowering in full sun. Tolerant of salt spray, and poor, shallow, rocky to sandy soils. Drought tolerant once established, and does not require summer irrigation except in hotter, inland climates. Do not overwater. Can be pruned to maintain shape and size immediately after flowering, but does not take well to heavy pruning. Intolerant of root disturbance. Can tolerate open, exposed sites in coastal climates but performs best in a more protected location further inland. Hardy in Zones 8-10.
'Skylark' is more tolerant of compacted, clayey soils and colder temperatures compared to the species. Hardy in Zones 7-10.
Noteworthy Characteristics
Ceanothus thyrsiflorus, commonly called blue mountain lilac or blueblossom, is a evergreen shrub native to the coastal chaparral and rocky, maritime, open and wooded slopes, bluffs and flats along the western coast of the United States from California north to Oregon. Mature plants can take on an upright form, reaching up to 20' tall with a similar spread. Individuals can also take on a more spreading habit, reaching only a few feet tall. The elliptic to ovate leaves have finely serrated margins and can reach 1.5" long and 0.5" wide. Terminal clusters of small, blue flowers bloom in from spring into early summer. This plant is a larval food source for multiple species of butterflies and moths, including the spring azure, echo blue, and California tortoiseshell. The flowers are attractive to insect pollinators and the seeds are eaten by birds and small mammals.
Genus name comes from keanothos which is an ancient Greek name relating to some plants in the buckthorn family.
The specific epithet thyrsiflorus means "flowers arranged in a thyrse", in reference to the shape of the infloresence
'Skylark' is a compact, dome-shaped to mound-forming selection of blue mountain lilac that features glossy, dark green foliage and a long, showy floral display with dense clusters of small, blue flowers nearly covering the shrub. The bloom period is also later than the species, starting in late spring and continuing into summer. Mature specimens can reach up to 5' tall and spread to fill a 7' area.
Problems
Generally free of pest and disease concerns, but watch for scale and aphids. Armillaria and phytophthora infections of the crown and roots are possible, but these fungal diseases are typically a symptom of too much moisture.
Uses
Suitable for seaside gardens, native gardens, pollinator gardens, Mediterranean gardens, and mixed borders. Use as a hedge, screen, or for erosion control on a slope or embankment.