Breezy blue perennials
Add some blue notes to the summer and autumn garden with these three gorgeous perennials, writes MICHAEL McCOY
Blue flowers have a universal appeal. I know lots of gardeners who won’t grow yellow flowers, and won’t willingly stand in the presence of oranges, but no-one rejects blue. And they have a reputation for being rare, and elusive, adding further to their appeal.
The truth is that there are quite a lot of blue-flowered plants although when they sit alongside some of the true, rich, sky-blues, such as the Caryopteris species (see page 29), you might find many lean towards lilac or mauve.
Blue is a colour that needs contrast if it’s to sing. Even when horticultural fashion swings around to single-colour gardens, as it occasionally does, it seems we all intuitively know not to try a blue garden. Blue on blue just makes you feel, well, blue. But blue with yellow and white sets the spirits soaring. Better still, as a base note among either the hotter end of the spectrum or cool pinks and mauves, it’s magical and, you could argue, essential.
Here’s a closer look at three cool-blue perennials. They all perform best in cool to warm temperate areas, and are quite tolerant of dry conditions once established.
SEA HOLLY (Eryngium spp.)
The two outstanding characteristics of eryngiums are their superb floral texture, taking thistle-like characteristics to truly fabulous places, and the curious steely quality of their colouring.
The blue-flowered species Eryngium bourgatii, E. x oliverianum and E. planum look like they’ve been spray-painted, often from one side, with a light coat of metallic blue. Most varieties within this category are about 60cm–1m in height, and are very long-lived perennials, requiring only a winter cutback to the ground. There are others, too, including biennials with flowers that look like tarnished titanium, and some huge, mounded, almost succulent strap-leafed plants over 2m tall with purple flowers.
Perhaps one of the showiest is E. bourgatii ‘Oxford Blue’, with cones of flowers surrounded by a spiny-looking ruff of bracts, all coated in blue, including the flower stems. I can’t think of any other flower that so convincingly gives the impression that the colour was externally applied, to all the floral parts.
Much more subtle in its colouring, but of more structural character, is our own native species, the blue devil (E. ovinum).
It is sensational popping up among low native grasses.
RUSSIAN SAGE (Salvia yangii)
The Russian sage, still most often known by its previous genus that naturally has you putting on an accent and rolling your ‘r’s – Perovskia – is now named, more prosaically, Salvia yangii. Arguably having lost a little exotic mystique in the process, the plant is still its superb self.
Emphatically vertical growth carrying grey foliage gives rise to upright, airy, spacious stems producing pale, velvety lilac flowers to 1–1.2m. The flowers go on for months, then fall to leave stems of ghostly silver, becoming more and more conspicuous as autumn turns to winter, and surrounding plants morph into their dormant blondes and browns. Like the Caryopteris species (opposite), this subtle effect is amplified by repetition. I confess I never noticed the silver on solitary plants, but in a decent sweep or a clump of at least half a dozen, it becomes one of their great virtues. Plants are cut down to woody stumps in winter, then weeded and mulched. Nothing else is required.
Russian sage is happiest growing in a dryish, perfectly drained soil. Some gardeners say they can’t make it happy. Others find that it thrives on neglect. It’s one of those plants that’s either going to grow easily for you, or not at all.
BLUE BEARD (Caryopteris x clandonensis ‘Heavenly Blue’)
Known as a perennial to its friends, Caryopteris ‘Heavenly
Blue’ is, in fact, a subshrub, meaning it has a woody base and herbaceous, annually replaced top growth that flowers now, in late summer, at about 80cm. And the flowers are bluer than blue – so blue that when you take a snap, you’ll have to convince your friends that you didn’t photoshop it.
They last for about three wonderful weeks, during which they’re crawling with bees, and after which they leave olive-green bracts stained with just a hint of inky blue, as if they’re dreaming of the glory days. The effect of these bracts is at its best when the plants are grown in sweeps – at least five together, and up to a dozen or so, winding through surrounding planting.
Sometime in winter, when your desire for tidiness and renewal starts to trump the joy of romantic decay, these plants should be cut back to stumps, down to about 10–15cm tall. That’s a great time to make sure any weeds that have taken hold are removed, and the plant is mulched and given a bit of a slow-release feed, ahead of the burst of new growth in spring.