Ceanothus arboreus ‘Trewithen Blue’
Family: Rhamnaceae
Common name: Trewithen Blue Island Ceanothus

Ceanothus arboreus is native to the Catalina Islands off the California coats and is the tallest member of the genus Ceanothus.  It has been widely cultivated in California and Europe and has been used in informal hedges, as screening, and in roadside plantings.  It can be easily trained into a small tree form.  Flowering typically occurs in late Winter and early Spring.  The species grows best at sites with well-drained soil and full or partial sun.  It tolerates cold to -10oC.  In California it requires some shade when grown in hot dry regions and this would also be true under local conditions.  Ceanothus generally have good tolerance of dry sites and, if irrigated, the timing should be such that the soil dries between irrigation cycles.

‘Trewithen Blue’ was selected in Cornwall, U.K., and given merit awards by the R.H.S. in 1967 and 1984.  It has an upright habit with a rounded crown with blue flower clusters up to 150 mm long, darker than in the species.  It can be grown as a specimen or espaliered and could probably be used for hedging.  There is very little experience of this species or cultivar in Australia but is worthy of trial planting.

Typical mature height: 5m
Useful in: Parks and reserves and possibly some street plantings
Sites for best growth: Best with well-drained sites