Plant of the Month: May
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Ceanothus arboreus 'Trewithen Blue' AGM
Common name: Catalina mountain lilac, tree ceanothus, California lilac
Family: Rhamnaceae
Vital statistics
Height and spread: 6m (20ft) x 8m (25ft)
Form: Evergreen shrub
Soil: Fertile and well drained, sheltered from cold winds.
Aspect: Full sun.
Hardiness: Frost hardy down to -5°C or somewhat lower |
Ceanothus arboreus 'Trewithen Blue' @ Hyde Hall
The Farmhouse at Hyde Hall faces due south. This south facing wall produces a wonderful planting opportunity as the microclimate it creates is a warm, sunny sheltered and fairly frost free situation. This enables us to grow a wide range of climbers and wall shrubs that like these warm conditions. A good example of such a wall shrub is Ceanothus arboreus 'Trewithen Blue' AGM, which we have growing against the front wall of the house. This plant is not self clinging and so needs a little guidance when growing against a wall, for instance by using horizontal wires. It should be pruned after flowering, and when grown against a wall it should be spur pruned to keep it flat, and flush with the wall. Traditionally Ceanothus flowers during April and May but growing in this warm situation this particular plant flowers sporadically from January onwards.
Ceanothus
The genus Ceanothus is native to North America, particularly California. Its name comes for the Greek word for a spiny plant.
The genus contains about 55 species of deciduous and evergreen shrubs from the USA and Mexico, usually found in scrub and woodland on dry slopes.
They are cultivated for their profusion of small flowers that range in colour from powder blue to deep purple, with a few having white, cream or pink flowers, which appear in spring and early summer.
Ceanothus tolerate drought, heat and cold, provided the soil is free draining, but they resent disturbance. They are quick growing but can be short lived and make an attractive addition to a shrub border or against a sunny wall.
Ceanothus arboreus 'Trewithen Blue'
This cultivar is a vigorous, wide-spreading, evergreen shrub with ovate to rounded, toothed, dark-green leaves, up to 10cm (4in) long.
In spring and early summer, fragrant, mid-blue flowers are borne in terminal and lateral panicles, up to 12.5cm (5in) long.
AGM
The RHS Floral B Committee awarded Ceanothus arboreus 'Trewithen Blue' an Award of Garden Merit and described it as a: Large vigorous evergreen spreading shrub. Leaves broadly oval or rounded, to 8cm (3.5in) long. Flowers deep blue, slightly fragrant, in panicles to 12.5cm (5in) long.
Cultivation
Grow in fertile, well-drained soil, in full sun sheltered from strong, cold winds. It can be trained against a wall where it will reach a greater height than in an open site.
Prune lightly after flowering, removing spent flower heads if practical, and dead or damaged wood.
If growing against a wall, trim outward facing shoots and those growing towards the wall. Cut back flower shoots to within two to four buds of the permanent framework.
Ceanothus is susceptible to honey fungus.
Propagation
Sow seed in a seedbed or in containers in an open frame in autumn.
Root semi-ripe cuttings in mid- to late summer.