Shrubby plumbago
Ceratostigma are always popular shrubs because they have the great merit of having blue flowers. The generic name refers to the horn-like outgrowths on the stigma. These are useful evergreen and deciduous shrubs, originally from China and the Himalayas, with five lobed blue flowers borne in spike-like clusters from late summer to autumn. They can be grown in sun and shelter; perhaps against a warm wall in a shrub or a mixed border. The varieties which we grow are perfectly hardy although shrubby species may experience some dieback after a cold winter. The shrubby species can therefore benefit from a light top pruning in spring to remove any deadwood, to keep them in shape, and encourage better flowering in the following season. C. plumbaginoides is also suitable as groundcover or in the rock garden and requires no pruning.
C. abyssinicum is the exception to the above in that, despite being a sturdy growing shrub with sky-blue flowers, it is only half hardy and is therefore probably only for the greenhouse or patio.
Otherwise these three species and varieties are perfectly hardy.
C. griffithii is a rounded evergreen shrub or sub-shrub which grows to around 3ft in height with a larger spread. The large flowers are bright blue in spike-like terminal clusters and the leaves turn red in autumn and winter.
C. willmottianum is a much more open branched, spreading, deciduous shrub with bristly stems. It will achieve a similar size in maturity to C. griffithii. The flowers are a pale blue with red-purple tubes in both axillary and terminal clusters.
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C. plumbaginoides only grows around 18in in height and is a deciduous perennial. The leaves are bright green with bristly margins and the terminal clusters of flowers are bright blue.
Ceratostigma can all be propagated in a variety of ways. Softwood cuttings in spring root quickly but semi-ripe cuttings in summer can also be successful. The habit of these plants means that they are easy to layer and they generally produce suckers from the base of the shrub which can be severed with some roots and replanted and grown on over winter in pots.
