'Dark Knight' stars in a symphony of blue
BLUE is an invaluable colour in the garden at this time of year when there are so many shades of yellow, orange and red. Even the smallest touch of blue here and there is enough to offer a contrast with the autumn colours and heighten them in the process.
Caryopteris gives intensely blue flowers in August and September. It generally goes by its correct botanical name, although various common names have been coined, such as blue mist, bluebeard and blue spirea.
Of the common names, blue spirea is probably the best because it describes the plant quite well. Those familiar with spirea will find it an easy enough leap to visualise the size, shape and growth habit of the plant. It also looks somewhat like a low-growing ceanothus.
Caryopteris is capable of growing to a bit over one metre tall and somewhat more than that in width. Quite often, it is treated as a pruned shrub, cut back hard in spring each year or every couple of years. When cut back, the plant is kept to a smaller, neater size and the new shoots are more upright.
These spikes carry clusters of small blue flowers in the angles of the leaves along the stems. The flowers have a pin-cushion look because of their spidery protruding stamens. Although the foliage is nettle-like, the plant is related to verbena. Mostly the flower colour is an intense purple-blue. Some are lighter and others darker and there are several named varieties.
'Kew Blue' is a popular variety with deep blue flowers over grey-green leaves. 'Heavenly Blue' is upright with rich blue flowers with a purple tinge. 'Dark Knight' has very dark blue flowers over silver-grey foliage.
'Arthur Simmonds' has grey-green leaves, silver underneath and rich blue flowers. 'First Choice' is a lovely dark purple-blue.
There are some golden-leaved and variegated varieties too. Apart from 'Worcester Gold', the yellow leaves of which make a good contrast, these are wishy-washy. Caryopteris also looks well with grey-leaved plants and can be used to enliven lavender and other greys after these have finished flowering.
The stems of caryopteris are spindly and it is not a very woody shrub. By cutting it back in spring, it becomes almost a herbaceous perennial. It should be set out where its late summer and early autumn blue will be most effective.
It is easy to grow in any ordinary soil that is well drained, but not too dry, and it likes a sheltered spot in sunshine to flower best.