Plant of The Month – Ceratostigma willmontianum
Few flowers have the ability to linger late into the year but as autumn draws to a close, the neat, gentian-blue heads of Ceratostigma willmottianum keep on going providing colour and interest in the garden, when most have given up. They sometimes persist for so long that in mild winters it is possible to find the odd flower on Christmas Day. The blue petals look even brighter set against the purple-tinted, quilled seed heads. The diamond-shaped, scarlet leaves, which colour up as the days shorten, radiate warmth on dark winter afternoons. As the year ends, the wiry stems and spent flower heads form a delicate silhouette; this is a plant that will please from June right through to the following spring.
Often called Chinese plumbago, this hardy, 1m (3ft) high shrub is one of eight species found in the Himalayas, south-east Asia and east Africa. It was first collected in 1908 by Edward “Chinese” Wilson and due to its popularity and great versatility in the garden, it received an Award of Merit in 1917.
Ceratostigmas are found naturally on the rocky slopes of hot, dry valleys, often in rain shadows, and therefore demand good drainage and an open, sunny position in the garden. In cold areas where winters are long, ceratostigma is best grown in a sheltered position against a sunny, south-facing wall.
In addition to willomntianum, another widely available form is Ceratostigma plumbaginoides, which is smaller and herbaceous. While it’s a great plant in its own right, I have always preferred the taller C. willmottianum as it has more of a presence, bears larger clusters of buds, has finer foliage and flowers for longer. Maintenance is also minimal, requiring only a cut back hard in late spring. All foliage and stems are left over the winter until you see where the new shoots break. If shoots appear along the stems give the plant a light trim. If shoots only appear at the base, cut hard back.
Ceratostigma is a versatile plant for the border, as it combines well with so many other plants. It can be great in the shrub border but will hold its own in a perennial scheme too. I like it combined with another of my favourites – penisetum orientale. The fluffy pink seed heads of the grass make the perfect partner for those dainty blue flowers. It can also look great next to the hotter colours of late summer, making it an ideal accompaniment for heleniums, dahlias and other grasses too. You just can’t go wrong with this little plant, so find some space and enjoy the treat the flowers will provide for years to come.