Blue is not a common colour in the world of flowers, especially in late summer and early autumn. Most shrubs have flowered by now as well, so to find a large blue-flowered shrub at this time of year must be considered a bonus. Welcome to vitex agnus-castus.
According to Wikipedia, it is also known as the chaste tree, chasteberry, Abraham’s balm, lilac chastetree or monk’s pepper, and is a native of the Mediterranean region. With so many non-scientific names, it will come as no surprise to discover it has long been in cultivation and has attracted many “myths, legends, and actualities about human sexuality.” Women believed that sleeping under it would keep them pure while their menfolk were away fighting war, while drinking tea made from the seeds and leaves were believed to cure venereal disease and precipitate abortions. Dan Hinkley refers to this latter use as Plan B!
It is usually mid August before the flowers start to appear here in sunny east Berkshire in the UK.
Three weeks later, and the whole bush is a mass of buzzing insects on blue flowers.
Vitex agnus-castus requires a sheltered sunny spot in well-drained soil. It prefers fertile growing conditions, but becomes pretty drought tolerant when established. Left to its own devices, this can become a shrub up to 25 feet in height, but is more manageable when grown as a wall shrub and pruned hard every spring to within a bud of the old wood. My specimen is now six years old although the pruning only began two years ago. It is definitely big and blue at this time of year.