Plant of the Month : Perovskia antriplicifolia Blue Spire

True-blue flowers are hard to come by, even more so late in the year when that crystal-clear autumnal light dramatises every colour. Perovskia atriplicifolia ‘Blue Spire’ provides a rare infusion of violet-blue from late summer into October and the spires of bee-friendly flowers are softened by finely cut aromatic leaves set on a branching silver-white frame.

It is commonly known as Russian sage and was named after the Russian count who first introduced it to Western gardens about 100 years ago. But this late summer/early autumn performer, a member of the Labiatae family, has its origins further east in the arid, rocky soil and wide open spaces of Afghanistan and the Himalayas.

Perovskia is a sub-shrub that grows annually from a woody base and gives out 3ft-4ft tall erect silver stems clothed in ovate, deeply cut and lobed greyish leaves. At the end of the summer its stems terminate in long panicles of tiny, soft-violet tubular flowers. The effect is of a bluish haze hovering above the border, which is particularly effective among the longer shadows and in evening light.

Perovskia leaves are also strongly aromatic when brushed or crushed and smell of both sage and lavender. The stems are deciduous and, with a little grooming and adjustment in late autumn, have a slender, upright, bleached presence in the garden that can last throughout winter. ‘Blue Spire’ is a real sun-worshipper and needs good drainage. It’s a great plant for growing on shallow chalk and will adapt well to seaside conditions too.

To get the best out Perovskia, it’s all about the pruning. To ensure you are not left with a mass of messy and uncontrollable growth, its best to hard-prune back to a little woody framework, no more than a few inches tall, just as they are beginning to leaf up. This will probably not be until mid-April. If plants are pruned too early and too hard they may simply give up and die. If in doubt, it is best to wait until May when they will be in full growth.

In planting schemes of grand proportions, Perovskia works well grouped en masse under big open skies. Its silver shoots masking the fading leaves of underplanted spring tulips and alliums as summer advances and eventually forming a shimmering blue haze when viewed from a distance. One of my favourite combinations would be to plant Perovskia with Geranium Patricia, Erigeron karvinskianus, Knautia Macedonia and Pestemon Hewels pink. This great little group of plants will provide you with colour pretty much all summer long.